the mobility of the trace metals copper, zinc, lead, cobalt, and nickel in tropical estuarine sediments, ebrie lagoon, cte divoire | springerlink

the mobility of the trace metals copper, zinc, lead, cobalt, and nickel in tropical estuarine sediments, ebrie lagoon, cte divoire | springerlink

Trace metals accumulate in the food web and can pose high risks to human health and aquatic biota. We investigated seasonal and spatial variations of Cu, Zn, Pb, Co, and Ni mobility in surface sediments (05cm) and their potential toxicity.

The sampling was carried out in three embayments of the Ebrie Lagoon (Cte dIvoire) during the rainy and dry seasons. The sequential and kinetic extraction methods were used to assess Cu, Zn, Pb, Co, and Ni mobility and their potential toxicity. Analysis of variance (ANOVA) was performed to ascertain spatial and seasonal differences.

The results showed that contrarily to Co, distribution patterns of Zn and Cu in the sediment fractions showed no spatial and seasonal variability. On the other hand, Pb and Ni distribution patterns varied highly across the bays but not seasonally. Nevertheless, repeated measurements over a long period of time should be carried out to better understand the seasonal variability of metal distribution in sediment phases. Cu, Pb, Co, and Ni were abundant in residual fraction (56.9371.66%) in the bays. On the contrary, a very high portion of Zn (up to 70%) could be remobilized. Cu, Pb, Co, and Ni formed mainly inert complexes in sediments, while Zn formed labile complexes. Zn could pose high risk to biota, Co and Ni a medium risk, and Cu and Pb a low risk.

A combination of both sequential and kinetic methods revealed that both Zn and Pb formed labile complexes in the exchangeable and iron/manganese oxide fractions. Sequential extraction showed high Pb concentrations in the iron/manganese oxides. Thus, Zn and Pb may be highly available, which confirmed fish Pb concentrations exceeding WHO safe limits found by previous studies. Therefore, potential mobility of metals could be better assessed by the exchangeable and iron/manganese oxide fractions obtained by sequential extraction methods.

Trace metals are of environmental concern because they persist in the environment, incorporate into the food web, and can pose adverse effects to wildlife and humans (Bonanno and Giudice 2010; Zheng et al. 2010; Du et al. 2013; Qiu 2015). Sediments are an important sink for trace metals (Kouassi et al. 2015; Mahu et al. 2015; Zhang et al. 2016). They are considered as appropriate indicators of metal pollution in aquatic systems. However, to what extent sediments can release trace metals into the water column is unknown in many watersheds in the world. Metals can be released from sediment through many processes, such as sediment resuspension and release, diffusion and advection from sediments, and biotransfer through organisms. Metals form both residual complexes and non-residual complexes in sediment systems. While the former are inert, non-residual complexes show gradual levels of mobility in the water column depending on their thermodynamic stability. The partition of metal ions between the aqueous and particulate phases critically controls the migration behavior and bioavailability of trace metals (Chakraborty et al. 2015). Bioavailability of a metal refers to the portion of metal solubilized from an environmental compartment and ready for uptake by biota. Determining total metal concentration alone in sediments cannot provide information about their mobility, bioavailability, and toxicity (Chakraborty 2012; Arfania and Asadzadeh 2015; Fernandes and Nayak 2015; Ma et al. 2016). In addition, the distribution scheme of metals in sediments can vary with time under the variation of physical, chemical, and hydrological conditions (e.g., tides, pH, ionic strength). Therefore, studying the dynamics of trace metal concentrations and complexes into different sediment phases is of critical importance to understand the potential adverse effects of contaminated sediments on regional or local scale.

Metal mobility in sediments (and soils) is estimated through kinetic and sequential extraction methods (Santos et al. 2010; Chakraborty 2012; Chakraborty et al. 2012a, b; Hamdoun et al. 2015), Diffusive Gradients in Thin Films technique, flow techniques, and Batch techniques. Each method/technique has its limits; however, combining two techniques or methods is more efficient than studying one alone (Gismera et al. 2004). Kinetic extraction study provides information about the concentrations and dissociation rate constants of weak and strong metalsediment complexes (Bermond and Varrault 2004; Fangueiro et al. 2005). Sequential extraction procedures operationally estimate metal concentrations in different phases of the sediment system. The procedure proposed by the Community Bureau of Reference (BCR) is one of the most used due to its high reproducibility. It describes four phases of the sediments. The exchangeable (including carbonates) fraction (F1) and reducible fraction (F2) are identified as direct effect fractions because they are readily absorbed in plants or released into the water column. The oxidizable fraction (F3) is an approximate indication of the less mobile metal pool (Chen et al. 2008). Finally, the residual fraction (F4) is inert and not mobile. Since kinetic and sequential extraction methods are sensitive and easy to implement, they can be used together in developing countries where there is little access to research facilities. This could be of great help in understanding the geochemical speciation of elements in soils and sediments.

Coastal waters, such as lagoons, contribute worldwide to the social and economic well-being of the inhabitants. Such ecosystems are threatened in terms of water pollution, conservation, and management, especially in West Africa because of an intense increase in anthropogenic pressures, including mining operations and agricultural, industrial, and urban activities. This is true for the Ebrie Lagoon, the largest lagoon system in Western Africa. Recent data suggest that sediments from this mangrove ecosystem are heavily contaminated in Cd, Zn, Pb, and Cu (Bakary et al. 2015; Kouassi et al. 2015). An abundant literature is available for metal speciation in tropical estuaries (Cuong and Obbard 2006; Chakraborty et al. 2015; Fernandes and Nayak 2015; Ma et al. 2016). However, trace metal fate varies with aquatic environments and little information on metal mobility is available in the Ebrie Lagoon for predicting their potential toxicity.

This study investigated the seasonal and spatial variations of Cu, Zn, Pb, Co, and Ni mobility in sediments and their potential ecological risks in the Ebrie Lagoon (Cote dIvoire). To address this objective, the BCR sequential and the kinetic extraction protocols were used. The relevance of this study is that remobilization of trace metals and low thermodynamic metal complex stability in sediments may increase their bioavailability in the water column.

The Ebrie Lagoon system (325 N, 445 W) has a total area of 566km2 with a length of 130km and a maximum width of about 7km. It is the largest lagoon bordering the eastern equatorial Atlantic Ocean in West Africa. The average depth is of 4.8m, with a few deeper areas especially around Abidjan. The study area (Fig.1) is surrounded by Abidjan City (6 million inhabitants) the capital of Cte dIvoire. In this area, intense human activities constitute sources of chemical contamination to surrounding waters that may cause public health problems (Affian et al. 2009; Kouassi et al. 2015). The waters around Abidjan are highly eutrophicated, and frequent oxygen depletion occurs as a result of the discharge of untreated sewage and industrial waste (Bakary and Yao 2015). Human pressures are numerous including urbanization, industrialization, agricultural, fishing, ship building, transport, sand extraction, aquaculture, and tourism. The geology of the study area has been well-described in Kouassi et al. (2015) and Tastet and Guiral (1994). Tertiary and Quaternary Period sediment basins overlay the Precambrian basement. Along the southern edge of the Ebrie Lagoon, marine sand, riverlagoon clay and sand, as well as clayey sand derived from the Quaternary continental plateaus, form a coastal strip that separates the Lagoon from the Atlantic Ocean. The sediments in the northern region of the Ebrie Lagoon include clayey sands and sandstone weathered from high continental plateaus that originate from the Quaternary period (Tastet and Guiral 1994). The stratigraphic column coarsens downward, with clayey, medium-grained, and coarse-grained sand overlaying Precambrian basement rocks (Kadio et al. 2010). Although no distinct stratigraphic sequence can be observed in the south, the sediment cover includes medium to very fine and coarse sands, muddy sediments, and silt (Tastet and Guiral 1994; Kouame et al. 2010).

The sediment samples were collected from three embayments in the estuarine part of the Ebrie Lagoon: Cocody, Banco, and Bietri Bays (Fig. 1). Three environmentally significant stations representative of each bay were selected upstream, midstream, and downstream. These stations receive industrial or domestic wastewaters from highly populated Abidjan communes including Yopougon, Adjame, Cocody, and Port Bouet (Fig. 1).

A total of 36 surface sediment samples (05cm) were sampled from the dry (FebruaryMarch) to the rainy season (AprilMay). About 500g of sediment was taken at each station using a Van Veen stainless steel grab of 0.02m2 area, following the USEPA (2001). Without emptying the grab, a sample was taken from the center with a polyethylene spoon (acid washed) to avoid contamination by the metallic parts of the dredge. The samples were sealed in plastic bags, transported to the laboratory at 4C, oven-dried at 60C, homogenized, and stored at 4C until analysis (Chakraborty 2012; Canuto et al. 2013; Qiao et al. 2013; Chakraborty et al. 2014; Fernandes and Nayak 2015). Each sample was sieved through a stainless steel mesh to remove any particle larger than 63m in size.

Additionally, overlying sediment waters (0.5m from the sediments) were sampled with a Niskin bottle, and pH, salinity, and dissolved oxygen were immediately determined with a multiparameter (pH/ORP/EC/DO/Temp) HANNA HI9828.

All chemicals and reagents used in the study were of analytical grade. Glass, plastics, and other laboratory ware were cleaned by soaking in 10% HNO3 solution overnight and then thoroughly rinsed with de-ionized water. Three replicates of each sample were analyzed, and the samples presented an error within 6%. Duplicate blanks were prepared and analyzed with each batch of digested samples. The operational conditions for the AAS were adjusted in accordance with the manufacturers guidelines to obtain optimal determination. The reliability of the sequential extraction protocol (modified BCR) was checked by comparing the sum of the four fractions (F1+F2+F3+R) with the total metal concentration measured using GIF-AAS (Qiao et al. 2013; Liu et al. 2018; Saleem et al. 2018). The recovery rates for heavy metals ranged from 93.5 to 109%.

The sediment sand fraction (<63m) was determined by mechanical sieving; then, the silt and clay fractions were separated by laser-size particle analyzer (LPSA, Mastersizer 2000) following procedure described in Ramaswamy and Rao (2006). Total organic carbon concentrations were obtained from Kouassi et al. (2015).

Sequential extraction was performed using a three-stage modified procedure recommended by BCR plus the residual fraction (Canuto et al. 2013; Qiao et al. 2013). All extractions were carried out for 16h (overnight) at room temperature, using a mechanical shaker. The extract was then separated from the solid residue by centrifugation for 20min at 3000rpm, and the resultant supernatant liquid was transferred into a polyethylene volumetric flask. The residue was washed by adding 20mL of deionized water, mechanically shaken for 15min on an end-over-end shaker (model Rotospin, Tarsons), and centrifuged for 20min at 3000rpm. The liquid aliquots were analyzed using an airacetylene flame atomic absorption spectrometer (AAS, Spectr AA100/Varian, Tokyo, Japan). The three extraction steps performed in this study can be broadly summarized as follows.

Step 1 (exchangeable and bound to carbonates). Exactly 40mL of 0.11M acetic acid was added to 1g of sediment sample in a centrifuge tube and shaken for 16h at room temperature. The extract was then separated from the solid residue by centrifugation, and filtrate was separated by decantation as previously described.

Step 2 (iron and manganese fraction). Exactly 40mL of freshly prepared hydroxyl ammonium chloride solution was added to the residue from step 1 in the centrifuge tube and re-suspended by mechanical shaking for 16h at room temperature. The separation of the extract collection of the supernatant and rinsing of residues were the same as described in step 1.

Step 3 (organic matter and sulfide fraction). The residue in step 2 was treated twice with 10mL of 8.8M hydrogen peroxide. First, 10mL of hydrogen peroxide was added to the residue 2 in the centrifuge tube. The digestion was allowed to proceed at room temperature for 1h with occasional manual shaking, followed by digestion at 852C for another 1h. During the digestion, the centrifuge tube was loosely covered to prevent substantial loss of hydrogen peroxide. Next, the centrifuge tube was uncovered and heating continued until the volume reduced to about 23mL. An additional 10mL of hydrogen peroxide was added to the tube, covered, and digested with cover at 852C for another 1h. Heating was continued as before until 23mL. Finally, 50mL of 1M ammonium acetate was added to the cold mixture and shaken for 16h at room temperature. The separation of the extract, collection of the supernatant, and rinsing of residues were the same as described in step 1.

Kinetic extraction experiments were conducted for sediments collected in February. Two (2) grams of sediments was added to 200mL of 0.05M EDTA solution (at pH6) in a 400-mL Teflon beaker, and the mixture was continually stirred with a Teflon-coated magnetic stirring. The ratio of the mass sediment to the volume of EDTA solution was set at 0.01, as the ratio provides sufficiently high metal concentrations in the extract to be accurately quantified, while requiring a minimum amount of sediment. A special effort was made to maintain a homogeneous suspension in order to avoid changing the mass/volume ratio during sampling. Larger mass/volume ratios would be undesirable, as they could cause problems with filtration (Chakraborty 2012). At set time intervals (0, 2, 4, 6, 8, 10, 15, 20, 25, 30, 45, 60, 120, 300, 420, 600, 1440, 1800, 2160min), 2mL of aliquots of suspension was filtered through a 0.2-m syringe filter (Millex, Millipore) and analyzed by AAS. The initial time for the kinetic measurement (i.e., t=0) was taken as the time just before the sediment was added to the EDTA solution. The liquid aliquots were analyzed using an airacetylene flame atomic absorption spectrometer (AAS, Spectr AA100/Varian, Tokyo, Japan).

Kinetic model proposed by Fangueiro et al. (2005) was used to investigate the kinetic speciation of Zn, Cu, Pb, Co, and Ni in surface sediments of the Ebrie Lagoon. According to Fangueiro et al. (2005), multiple first-order extraction reactions may take place simultaneously, having rates that are assumed to be independent on each other. Each reaction rate can, thus, be expressed as:

where qi represents the quantity of desorbed metal from binding location , Qi represents the quantity of desorbed metal from binding location at equilibrium, and ki is the rate constant of the extraction reaction for compartment . Integrating Eq. (1) for the initial conditions Q1 (t=0)=0 and Q2 (t=0)=0 and rearranging the solution yield:

The parameters Q1, Q2, k1, and k2 in this equation were evaluated using Excels Solver optimization package by an iterative approach. As fitting criterion, the sum of squares of residuals between experimental metal concentration data and calculated data led to a minimum by changing progressively Q1, Q2, k1, and k2 values. In order to facilitate the comparison of Q1, Q2, and Q3values obtained for metals in sediment samples, those values were re-calculated as proportions (%Q1), (%Q2), and (%Q3) of total content:

During the sampling period, the water pH, salinity, and dissolved oxygen did not vary significantly between the dry (FebruaryMarch) and rainy (AprilMay) seasons at the watersediment interface (p<0.05, N=36) as shown in Tables S1 and S2 of the Electronic Supplementary Material. On the contrary, water pH, dissolved oxygen, and salinity varied significantly (p<0.05, N=36) between the bays (Tables S1 and S2 in the Electronic Supplementary Material). The average water pH followed the order Cocody (8.050.27)>Banco (7.980.22)>Bietri (7.510.22), the average water salinity order was Banco (31.92.72psu)>Bietri (28.14.96psu)>Cocody (27.23.74psu), while the average dissolved oxygen concentration was higher at Cocody (4.242.56mgL1), followed by Banco (2.072.50mgL1) and Bietri (0.540.60mgL1).

Sediment texture results showed that sediments were dominated by sand fraction (8386%) irrespective of the bays (Table S3 in the Electronic Supplementary Material). No spatial or seasonal difference was observed within and among the bays.

The geochemical fractionation of Zn in sediments from Banco, Bietri, and Cocody Bays (all bays combined) during the dry and rainy seasons is shown in Fig.2; the spatial variations are depicted in Fig.3. The results showed that a major portion of Zn is highly associated with the exchangeable fraction (F1) with percentages varying from 43.5 to 50.7% of total concentration (Figs.2a and 3a) irrespective of the bay and the season. This is equivalent to 70.7100gg1 of Zn concentration out of total of 163198gg1. On the contrary, Zn bounded to the residual fraction (R) (Figs. 2d and 3d) showed very low percentages (24.630.8%). One-way ANOVA analysis (p<0.05) showed no significant difference in all fractions between the seasons. With regard to spatial variation, only Zn concentration in the iron/manganese oxide fraction showed a significant difference (p<0.05) between Banco and Bietri Bays and between Bietri and Cocody Bays.

Seasonal variations in average percentages of metal concentrations in sediment binding phases (all stations of the Banco, Bietri, and Cocody Bays combined). Vertical bars indicate variations among the stations

A similar Zn chemical fractionation distribution scheme: exchangeable and bound to carbonates (F1)>residual (R)>iron/manganese (F2)>organic matter and sulfides (F3) was observed during the two seasons in all the bays.

As shown in Figs. 2d and 3d, the residual phase was found to be the most abundant Cu fraction with an average percentage varying between 62.1 and 69.8%. Among the non-lithogeneous phase, organic matter was the major Cu scavenger with an average percentage ranging between 16.0 and 25.3% (Figs.2c and 3c). This corresponds to 12.126.0gg1 out of total Cu concentration of 75.6103gg1. There was no significant difference (ANOVA, p<0.05) between the seasons for Cu concentrations in sediment fractions. Similarly, there was no significant difference (p<0.05) between different bays for Cu concentrations in the residual and exchangeable fractions. As for the iron and manganese oxide phase (F2) (Fig. 3b), the average Cu concentration was significantly higher (p<0.05) in Banco and Cocody Bays compared to that in Bietri Bay. Furthermore, the fraction of the total Cu associated with the organic matter binding phase (Fig. 3c) was significantly higher in Bietri Bay than that in Banco Bay. The Cu fractionation showed similar distribution pattern in all bays and seasons: residual (R)>organic matter and sulfides (F3)>iron/manganese (F2)>exchangeable and bound to carbonates (F1).

Figures2d and 3d showed that Pb was primarily associated with the residual fraction with an average percentage ranging from 61.5 to 68.2%. The iron/manganese phase was the most important non-residual fraction, with an average proportion varying between 12 and 22% (Figs. 2b and 3b). In terms of concentration, this is equivalent to 7.3010.8gg1out of total Pb concentration of 61.149.3gg1. The Pb percentages in the sediment fractions showed no significant spatial and seasonal variability (p<0.05). Moreover, the Pb chemical fractionation pattern was residual (R)>iron/manganese (F2)>organic matter (F3)>exchangeable and bound to carbonates (F1) irrespective of the season.

On the contrary, Pb chemical fractionation pattern varied with the bay. In Bietri and Cocody Bays, the pattern was residual (R)>reducible (F2)>organic matter (F3)>exchangeable and bound to carbonates (F1), while that of Banco bay was residual (R)>organic matter (F3)>iron and manganese (F2)>exchangeable and bound to carbonates (F1).

The results of seasonal and spatial variations of Co percentages in sediment fractions are shown in Figs. 2 and 3. The residual fraction was the most important Co binding phase with an average percentage varying between 56.9 and 66.1% (Figs. 2d and 3d). The percentages of Co in the non-residual fractions were comparable. Only the Co concentrations in the iron and manganese oxide fraction (Fig. 2b) were significantly higher (p<0.05) in the rainy season than in the dry season. The average Co concentration in the all fractions did not vary significantly (p<0.05) among the bays. On the contrary, the seasonal chemical fractionation pattern of Co varied with the season and the bay. The fractionation pattern in sediment was residual (R)>exchangeable and bound to carbonates (F1)>organic matter (F3)>iron and manganese oxides (F2) in the dry season and residual (R)>organic matter (F3)>iron and manganese (F2)>exchangeable and bound to carbonates (F1) in the rainy season. As for spatial variations, different cobalt distribution patterns were observed in the bays: residual (R)>iron/manganese (F2)>organic matter (F3)>exchangeable and bound to carbonates (F1) in Banco Bay, residual (R)>organic matter (F3)>exchangeable and bound to carbonates (F1)>iron/manganese (F2) in Bietri Bay, and residual (R)>exchangeable and bound to carbonates (F1)>iron/manganese oxides (F2), >organic matter (F3) in Cocody Bay.

Figures 2 and 3 illustrate the geochemical partitioning of Ni in sediment fractions. The dominant Ni phase was the residual fraction with an average percentage ranging from 70.2 to 72.4% (Figs. 2d and 3d). The Ni percentages in the non-residual fractions were comparable, although F1 fraction showed slightly higher values (11%; equivalent to 4.08gg1 out of Ni total concentration of 37.05gg1). ANOVA analysis showed no significant spatial and seasonal variability (p<0.05) in Ni percentages in all sediment fractions. Ni distribution schemes varied across the bays but not seasonally. During both the dry and rainy seasons, the Ni distribution pattern was residual (R)>exchangeable and bound to carbonates (F1)>organic matter (F3)>iron/manganese (F2).

The spatial distribution patterns of Ni were residual (R)>organic matter (F3)>exchangeable and bound to carbonates (F1)>iron/manganese (F2) in Banco and Cocody Bays and residual (R)>exchangeable and bound to carbonates (F1)>organic matter (F3)>iron/manganese oxides (F2) in Bietri Bay.

The average concentrations of non-residual Zn, Cu, Pb, Co, and Ni in sediments varied between 114 and 148gg1, 22 and 39gg1, 20 and 26gg1, 4 and 5gg1, and 7 and 12gg1, respectively (Table S4 in the Electronic Supplementary Material). The sum (%F1+%F2+%F3) representing the percentage of the non-residual fraction was calculated to assess Zn, Cu, Pb, Co, and Ni mobility (Fig.4). For all bays combined, Zn had the highest non-residual fraction proportion during the dry (74.1%) and rainy (71.3%) seasons. During the whole study period, the percentage of Zn non-residual fraction varied from 69.1 at Banco to 75.4% at Cocody and was much higher than the ones at Cu, Pb, Co, and Ni (less than 40%). The mobility percentage of the elements followed the order dry>rainy for Zn, Co, and Pb and rainy>dry for Co and Ni. With regard to the potential mobility of each metal in the bays, the decreasing mobility trends were Cocody>Bietri>Banco for Zn, Cu, Pb, and Ni and Banco>Bietri>Cocody for Co with no significant difference.

The extraction curves obtained from the kinetic extraction are given by Figs.5, 6, and 7. Two distinguishable features can be distinguished. The first part of all the curves: t<45min in Cocody Bay and 045min in Cocody Bay and t>60min in Banco and Bietri Bays for Zn, and t>60min in all the Bays for Cu and Co, t>45min in all the bays for Pb and Ni, corresponds to the fraction (Q2) of less extractable metals with moderate thermodynamic stability and dissociation rates k2. The k1 values ranged from 9.3102 to 101min1 for all metals, while those of k2 varied between 106 and 13103min1 (Table 1). Thus, k1 values were higher than k2 values.

The total mobility (%) of Zn, Cu, Pb, Co, and Ni was estimated by the sum (%Q1+%Q2). The results are shown in Table 1. In all the bays, the Zn total mobility was the highest, varying between 77.62 and 88.53%. Table 1 also indicated that an important portion (65 to 94%) (%Q3) of Cu, Pb, Co, and Ni was not extracted by EDTA. Using values of total mobility percentage (%Q1+%Q2) in different bays, it can be observed that the order of metal mobility was Zn>Pb>Co>Ni>Cu in Bietri and Cocody Bays, while the one in Banco Bay was Zn>Co>Ni>Pb>Cu.

In the Ebrie Lagoon, the dry season corresponds to intrusion of marine waters from the Atlantic Ocean, which increases water salinity, pH, and redox potential values. On the contrary, during the rainy season, precipitations and freshwaters from the Comoe River dilute lagoon waters and decrease water salinity, pH, and redox potential values. The absence of significant seasonal variability in water characteristics found in this study could be attributed to the fact that the high rainy season did not reach its peak over the study period. On the contrary, the observed significant spatial variability in water pH, dissolved oxygen, and salinity results from differences in the proximity of the bays to seawater or freshwater discharges, difference in water bathymetry and wastewater inputs as reported by Kone et al. (2009). The results also underlined a relatively permanent anoxia at most stations in Banco and Bietri Bays and occasional hypoxia in few stations in Cocody Bay. This indicates that the sediments of Cocody, Banco, and Bietri Bays were predominated by reducing conditions. The observed deoxygenation of the Ebrie Lagoon waters is attributive to anthropogenic nutrient inputs, which can result in primary production and subsequent high oxygen consumption (Altieri and Gedan 2015). In addition, water stratification could be a complementary cause of the observed deoxygenation. The local geology consists of sediment deposit. Our results showed that the sediments were sandy, and the proportion of sand, silt, and clay was similar irrespective of the seasons and the bays. This could indicate that the bays are not environmentally different in terms of sediment discharges. The relative spatial homogeneity in sediment composition could also be related to the position and the similar depths of the sampled stations. Moreover, Kouassi et al. (2015) found that the TOC content in the sediments from the present study ranged between 2.42 and 3.25% and did not vary among the Cocody, Banco, and Bietri Bays (Table S3 in the Electronic Supplementary Material). It has been reported that TOC increases with finer particles; thus, the lack of significant variation in TOC content between the bays could be a consequence of the relative spatial homogeneity of sediment texture.

It should be noted that total metal concentrations in sediments from this study, their sources, and spatial distributions have been previously described in Kouassi et al. (2015) (Table S4 in the Electronic Supplementary Material). The ranges of metal concentrations in the Cocody, Banco, and Bietri Bays were as follows: 61.1418gg1 for Zn, 33.25182gg1 for Cu, 9.19132gg1 for Pb, 8.2018.4gg1 for Co, and 1.3573.1gg1 for Ni. These results showed that Ebrie Lagoon was one of the most contaminated tropical estuaries in trace metals. However, total concentration cannot provide information about the fate, bioavailability, and toxicity of sediments. Therefore, the results of the present study focused on the potential mobility of trace metals from the sediments to the overlying waters.

The proportions of Zn, Cu, Pb, Co, and Ni concentrations in the exchangeable and bound to carbonates, iron/manganese oxides, organic matter, and residual phases of the Ebrie Lagoon sediments did not vary significantly among the seasons from February to May. The sorption of metals on sediment phases is a complex physicalchemical process. Changes in environmental conditions, such as pH, salinity, redox potential, organic matter, and temperature could influence metal distribution in sediment fractions (Chakraborty and Babu 2015; Wang et al. 2015). For example, under reducing conditions, iron/manganese oxides can dissolute and be released into the water column. Similarly, part of metal bound to organic matter fraction can be released into the water column in anoxic conditions (Feng et al. 2014). At lower pH (<4), metal adsorption efficiency decreases while at higher pH metal adsorption increases. In addition, high water salinity may increase metal desorption.

During the sampling period, the average water pH, dissolved oxygen, and salinity did not differ significantly among the seasons. This may in part explain why metal concentrations in sediment binding phases did not vary between the seasons from February to May 2012. On the contrary, pH, dissolved oxygen, and salinity at the watersediment interface varied significantly between the bays, but no significant spatial variation was observed in metal levels in the sediment phases among the bays.

Sediment texture plays a key role in trace metal distribution in sediments. Trace metal concentrations in sediment increase with finer particles (Yao et al. 2015). Consequently, the clay fraction accumulates more metal than the silt and sand fractions because of their larger specific surface and higher TOC content. However, the influence of sediment size fractions on metal mobility is hardly predictable. In this study, both the sedimentary metal proportions and the sediment grain size composition did not show significant seasonal and spatial changes (Table S5 in the Electronic Supplementary Material). Furthermore, we found moderate to significant correlations between grain size composition and percentages of metal bound to sediment phases (Table S6 in the Electronic Supplementary Material). For example, with regard to Zn, moderate to significant correlations were obtained between iron/manganese oxides and silt (r=0.54) and clay (r=0.40) in May; organic matter and sand (r=0.57) and clay (r=0.62); exchangeable and bound to carbonates and sand (r=0.49) in February; between organic matter and sand (r=0.68) and silt (r=0.56) and clay (r=0.52), exchangeable and bound to carbonates and sand (r=0.42) in April. These correlations may indicate a relative link between metal proportion in sediment phase fractions and sediment texture. Nevertheless, additional studies taking other factors, such as physical transport, solidliquid equilibrium of trace metals between pore water and sediment, larger geographic areas, and longer study periods, into account should be carried out to better explain the seasonal variability of metal fractionation observed in this study. Koretsky et al. (2006) showed similar Zn, Cu, Pb, and Co fractions in sediments from the Asylum Lake (USA) between winter and summer. In contrast, Iwegbue et al. (2007) observed that Zn and Pb levels in the Ase River sediment phases (Nigeria) were influenced by the season, which is in stark contrast with our observations. These findings show that seasonal and spatial variations of metal distribution in sediment binding phases are local specific.

Contrary to Co, Zn and Cu distribution patterns in the sediment fractions showed no spatial and seasonal variability. On the opposite, Pb and Ni distribution schemes varied highly across the bays but not seasonally. The different distribution patterns observed among the metals could result from different affinities of metals for sediments and different metal sources. Sediment heterogeneity (grain size composition) in time and space could explain spatial variability as it has been reported by Kang et al. (2017) in the Jiaozhou Bay. In addition, dredging activities in the Bietri Bay may have released bottom sediments to the surface during the sampling period. According to Kouassi et al. (2015), the major sources of metals in the bays of the Ebrie Lagoon are water runoffs and diffuse residential water discharges from neighborhoods close to bays. The diffuse sources of metals in these bays could result in similar metal distribution patterns as mentioned by Fonseca et al. (2013). The seasonal changes in Co chemical distribution pattern in the sediment could be attributed in part to mutual transformations of sediment fractions as mentioned by Feng et al. (2014).

Zinc partitioning in the sediment phases was controlled by the exchangeable fraction in the Ebrie Lagoon bays during the study period. This may indicate that carbonates are major scavengers of Zn in the Ebrie Lagoon sediments. Previous studies have shown that anthropogenic metals are predominantly found in the exchangeable and carbonate fraction (Crdenas et al. 2010; Gao and Chen 2012), which are vulnerable to small changes in environmental conditions, such as those caused by human activities. Kouassi et al. (2015) mentioned anthropogenic sources of Zn in the Ebrie Lagoon. Thus, high percentages of Zn obtained in the exchangeable fraction in our study could result from the anthropogenic sources of Zn. The proportion of the most mobile phase of Zn (26.770.0%) bound to sediments found in this study is comparable to the one obtained in systems under anthropogenic influences like the Shantou Bay in China (41%) (Qiao et al. 2013), but higher than those measured in systems in which Zn was from natural origin like in the Bohai Bay in China (8.2%) (Gao and Chen 2012) and the Sal Estuary in Brazil (12%) (Canuto et al. 2013). On the contrary, Pb and Ni showed high proportions in the residual phase of the sediments suggesting that these metals derived mainly from natural sources.

Kinetic extraction results revealed that Zn was rapidly extracted by EDTA, while Cu, Pb, Co, and Ni were slowly extracted. Up to 6594% of Cu, Pb, Co, and Ni complexes were not extracted by EDTA. This finding indicates that Cu, Pb, Co, and Ni formed mainly inert complexes in sediments, while Zn formed labile complexes. Thus, Cu, Pb, Co, and Ni may be less available for biota, while Zn may be highly available. Kinetic results also showed that the order of metal mobility in the Bietri Bay was similar to that in the Cocody Bay, but it was different to the one in the Banco Bay. For example, Pb ranked as the second most mobile element in the Bietri and Cocody Bays but was the last but one mobile element in the Banco Bay. This finding confirms the spatial variability of Pb mobility revealed by sequential extraction results. The lower mobility of Cu, Co, and Ni has been also reported in other studies (Fangueiro et al. 2005; Chakraborty 2012). In contrast, Hamdoun et al. (2015) obtained high mobility of Cu in marine sediments from Ouistreham and Concarneau Harbors (France) and Pool (UK). Leleyter et al. (2012) reported high and low mobility for Pb and Zn, respectively, in estuarine sediments in France. Overall, these observations show that the mobility of metals can vary widely in estuaries because there are numerous factors that determine their speciation.

To better understand metal mobility, we performed correlation analysis between non-residual fractions F1, F2, and F3 obtained by sequential extraction with the labile (Q1+Q2) and the inert (Q3) fractions obtained by kinetic methods (Table 2). A correlation with the labile fraction indicates formation of labile complexes, while a correlation with the inert fraction indicates formation of thermodynamically inert complexes in the sediment phases (Chakraborty et al. 2012a; Chakraborty 2012).

We found that Zn, Cu, Pb, and Ni bound to the organic matter fraction of sediments were strongly correlated with their inert fractions. This suggests that Zn, Cu, Pb, and Ni formed inert complexes with organic matter and are therefore not mobile. Our finding corroborates previous studies reporting that organic matter fraction is an approximate indication of the less mobile metal pool (Chen et al. 2008; Ma et al. 2016). Thus, using the sum of non-residual fractions obtained by sequential extraction to evaluate metal mobility in the Ebrie Lagoon may overestimate the mobile metal pool as mentioned by Chakraborty et al. (2012a) for the Godavari estuary in India.

Correlation analysis also showed that Cu formed thermodynamically stable complexes in all the sediment phases. Zn and Pb formed labile complexes in the exchangeable and iron and manganese oxide fractions, while Co formed labile complexes in the iron and manganese oxides. These results indicate that a high total concentration of Zn and Pb in the exchangeable and the iron/manganese phases in the Ebrie Lagoon sediments could result in significant bioaccumulation of these elements. Contradictory to the kinetic extraction results, Pb may be available to biota because sequential extraction showed relatively high amounts of Pb in the iron/manganese phase (7.3010.8gg1). The significant bioavailability of Pb in the Ebrie Lagoon is consistent with previous studies that found fish Pb concentrations exceed the safe limits (Coulibaly et al. 2012; Yapi et al. 2012). This result shows that combination of both sequential and kinetic extraction methods better explains Pb availability than the kinetic extraction method alone. We concluded that potential mobility of metals in the Ebrie Lagoon could be better assessed through the exchangeable fraction and the iron/manganese oxide fraction obtained using sequential extraction methods.

The Risk Assessment Code (RAC) was determined based on the percentage of total metal concentration in the exchangeable and acid soluble fraction (F1). This fraction is considered the most unstable and reactive phase, which has greater potential for adverse effects on the aquatic environment (Jain 2004). Based on the RAC scale, sediments collected from the Ebrie Lagoon could pose a high risk relative to Zn and a medium risk for Co and Ni. The RAC values of Pb and Cu revealed low risk (Fig.8). Thus, it can be concluded that Zn was the most bioavailable metal in the Ebrie Lagoon. This is confirmed by previous studies that found high Zn concentrations in fish and mollusks compared to other metals (Coulibaly et al. 2012; Bakary et al. 2015). On the contrary, this study shows that Pb was one of the less available metals in the Ebrie Lagoon system, which does not reflect concentrations exceeding WHO/FAO health limits reported in Cote dIvoire lagoon systems (Coulibaly et al. 2012; Yapi et al. 2012; Bakary et al. 2015). RAC evaluates qualitatively the potential risk of metals and does not take into account total metal concentration. The results of sequential extraction and kinetic studies performed in the present work suggest that the high concentrations of Pb found in biota from the Ebrie Lagoon revealed by previous studies resulted from high accumulation of Pb in the iron and manganese oxide phase. Therefore, RAC may underestimate Pb risk in the Ebrie Lagoon because it is limited to the exchangeable fraction in assessing the risk.

The mobility and potential risk of Zn, Cu, Pb, Co, and Ni were assessed in the Ebrie Lagoon using kinetic and sequential extraction methods from February 2012 to May 2012. This research demonstrates that percentages of Zn, Cu, Pb, Co, and Ni concentrations in the exchangeable and bound to carbonates, iron/manganese oxides, organic matter, and residual phases did not vary significantly among the bays and the seasons from February to May. Comparing kinetic and sequential extraction results, we found that high concentrations of Zn and Pb in the exchangeable and in the iron/manganese phase in the Ebrie Lagoon sediments could result in significant bioaccumulation of these elements. It was concluded that potential mobility of metals in the Ebrie Lagoon could be better assessed by the exchangeable fraction and the iron/manganese oxide fraction obtained by sequential extraction methods. Our study also revealed that Zn was the most mobile metal followed by Pb, while Co, Ni, and Cu were less available for biota in the Ebrie Lagoon. The Risk Assessment Code (RAC) results showed that Zn could pose high risk to biota, Co and Ni a medium risk, and Cu and Pb a low risk.

Long-term changes in trace metal proportions in sediments may occur; therefore, measurements over a longer study period as well as complementary studies including DGT (diffusive gradients in thin films) method and metal accumulation in organisms should be conducted to better understand the trace metal dynamics and the level of metal pollution.

Article with DOI 10.1007/s11368-018-2062-8, written by N. L. B. Kouassi et al., was originally published electronically on SpringerLink on 23 June 2018 with open access. Authors decision to cancel Open Choice and copyright changed to Springer-Verlag GmbH Germany, part of Springer Nature and the article is distributed under the terms of copyright.

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We are thankful to the Director of Centre de Recherches Oceanologiques for his encouragement and support. Unconditional help (to determine total metal concentrations in the sediments by AAS) from the Director of INP-HB, Yamoussoukro, is gratefully acknowledged. A special thank you goes to the reviewers for their critical contribution.

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made.

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Kouassi, N.L.B., Yao, K.M., Sangare, N. et al. The mobility of the trace metals copper, zinc, lead, cobalt, and nickel in tropical estuarine sediments, Ebrie Lagoon, Cte dIvoire. J Soils Sediments 19, 929944 (2019). https://doi.org/10.1007/s11368-018-2062-8

solid-phase partitioning and release-retention mechanisms of copper, lead, zinc and arsenic in soils impacted by artisanal and small-scale gold mining (asgm) activities - sciencedirect

solid-phase partitioning and release-retention mechanisms of copper, lead, zinc and arsenic in soils impacted by artisanal and small-scale gold mining (asgm) activities - sciencedirect

ASGM-impacted soils from Davao de Oro, Philippines were evaluated.ASGM-impacted soils were highly contaminated with As, Pb and Zn.Cu, Pb, Zn and As in the contaminated soil came from sulphide minerals.Pb and Zn were strongly retained in the soils via adsorption to HFOs and clays.Cu and As release from the historic ASGM site exceeded environmental standards.

Artisanal and small-scale gold mining (ASGM) operations are major contributors to the Philippines annual gold (Au) output (at least 60%). Unfortunately, these ASGM activities lacked adequate tailings management strategies, so contamination of the environment is prevalent. In this study, soil contamination with copper (Cu), lead (Pb), zinc (Zn) and arsenic (As) due to ASGM activities in Nabunturan, Davao de Oro, Philippines was investigated. The results showed that ASGM-impacted soils had Cu, Pb, Zn and As up to 3.6, 83, 73 and 68 times higher than background levels, respectively and were classified as extremely polluted (CD=30228; PLI=5.534.8). Minerals typically found in porphyry copper-gold ores like pyrite, chalcopyrite, malachite, galena, sphalerite and goethite were identified by XRD and SEM-EDS analyses. Furthermore, sequential extraction results indicate substantial Cu (up to 90%), Pb (up to 50%), Zn (up to 65%) and As (up to 48%) partitioned with strongly adsorbed, weak acid soluble, reducible and oxidisable fractions, which are considered as geochemically mobile phases in the environment. Although very high Pb and Zn were found in ASGM-impacted soils, they were relatively immobile under oxidising conditions around pH 8.5 because of their retention via adsorption to hydrous ferric oxides (HFOs), montmorillonite and kaolinite. In contrast, Cu and As release from the historic ASGM site samples exceeded the environmental limits for Class A and Class C effluents, which could be attributed to the removal of calcite and dolomite by weathering. The enhanced desorption of As at around pH 8.5 also likely contributed to its release from these soils.

distribution and health risk assessment of heavy metals in surface dusts of maha sarakham municipality - sciencedirect

distribution and health risk assessment of heavy metals in surface dusts of maha sarakham municipality - sciencedirect

Using the case of Maha Sarakham municipality, the research aims to monitoring the impact of urban land use and particle size distribution on the heavy metal (HM) contamination in surface dusts and carried out research into the exposure and health risk assessment of heavy metals on the fine size dusts. Samples were collected from five function areas. The contents of HM (lead, zinc, copper, and cadmium) in surface dusts were determined. Results showed only Zn concentration tended to increase with decreasing particle sizes. Results revealed the highest zinc concentrations from all areas. The parking lot samples contained the highest amount of heavy metals. HIs for all metals were lower than their threshold values, indicating without health hazards. The study will be beneficial for the municipality in terms of non-point source pollution control/management to promote the health of urbanites.

thailand smelting and refining co., ltd

thailand smelting and refining co., ltd

Built on the honesty and integrity of the AMC Plc group(www.amcgroup.com), Thaisarco Trading as a division of Thaisarco Smelting and Refining Co Ltd is committed to its customers and the communities. Thaisarco Trading professionally manages complex and long-term engagements whilst focusing on close and trustful cooperation with its customers to create mutual benefit.

When buying metal products for our clients, we only deal with medium to large sized, well established suppliers, and within the AMC Group, who all follow and understand high standards and are proven to be reliable business partners.

We work for long-term partnerships with our customers. The quality of the relationship between a client and a supplier is an important factor in any successful business transaction, and Thaisarco Trading makes great efforts to develope these long term and trustful relationships

Thaisarco Trading is a Division of THAILAND SMELTING AND REFINING CO.,LTD.(www.thaisarco.com), a world wide leading producer of Tin. The trading division was formed in 2008 and focuses its activities on the Thai and other South East Asian markets.

Thaisarco Trading delivers a full range of quality metal products, from raw materials to scrap Metals. We deal with all Ferrous and Non-Ferrous Metals, including Copper,Nickel, Aluminum, Cobalt, Tin, Zinc, Tungsten, Chrome,a full range of metal Alloys in ingot, powder and other forms, as well as a wide range of minor and exotic metals, and we are always ready to find tailor made solutions for our customers.

Being a part of the global AMC Plc group of companies (www.amcgroup.com) we benefit from a world wide sourcing net, enabling us to always offer the best quality product at the best price thereby ensuring the competitiveness of our valued customers.

Thaisarco Trading supplies foundries producing castings for aerospace application and land based turbines with the high purity metals necessary for their production. These casting will have the ability to perform in the harsh environments coping with the high temperatures and forces that are exerted on them. These metals include cobalt, chromium, and nickel.

Thaisarco Trading supplies many alloys and metals which are used by their foundry customers to produce the rich variety of alloys required for the many different applications within the automotive sector. Examples would be camshafts, crankshafts, valves, engine and gearbox casings and turbochargers.

Track and turret castings are produced by our customers using ferro alloys including ferro silicon, ferro manganese, ferro molybdenum; ferro chromium, ferro vanadium and nickel all play a part in the production of impact and wear resistant castings.

Our customers making castings for this sector use high purity, low residual metals and alloys to produce castings that work in hostile environments. Niobium, ferro niobium, ferro molybdenum, ferro vanadium, nickel and chromium would be used in this sector.

Policies Supply Chain Policy Code Of Conduct Grievance Mechanism Procedure Mine Visit, Due Diligence Report Quality Policy Environmental Policy Safety Policy Energy Management Policy Community Relations and Social Responsibility Policy Drug and Alcohol Policy Ethical Policy

AMC Group Website : Keeling & Walker Limited (Tin Oxide) William Rowland (Non Ferrous/Ferrous, Minor Metals etc.) Amalgamated Metal Trading Limited Mil-Ver Metals (Secondary Aluminium Ingots, Alloys etc.)

deister concentrating table

deister concentrating table

ThePlat-ODeister Concentrating Shaker Table exemplifies simple, low cost, high quality equipment for the separation and recovery of the free mineral in ores containing gold, silver, platinum, copper, tin, lead, zinc, iron and other minerals having a similar range of specific gravities.

The surface of this type table deck lies in two or more substantially parallel horizontal planes. The lowest plane, extending forward from the feed end, constitutes the greater portion of the deck surface and is known as the stratification and primary concentration zone. The highest plane, known as the plateau, or cleaning zone, extends back from the concentrate discharge end and is connected to the lower plane, along a diagonal line, by a bevelled strip known as the resistance plane. The upward slope of this resistance plane is just steep enough to allow the mineral strata to advance, but at the same time, holds back the upper and sand strata; thus forcing a constant, well defined line of separation between the two.

The standard riffling system on this type table consists of wide, flat riffles, longitudinal to the deck and covering all but the plateau or cleaning zone. These riffles are so spaced as to leave comparatively narrow channels for carrying heavy minerals only, with consequent displacement of the sand from between them; thus causing the pulp to spread out in a thin bed which permits more rapid and thorough stratification of the mineral and sand.

These tables are made in three types: triplex plateau sand table; single plateau fine sand table; and single plateau slime table. Each of these is in turn, by proper combination of riffling, height of plateau, internal arrangement of head motion, rate of reciprocation and length of stroke, assembled for the particular work it is to perform. In all other respects, insofar as general shape, foundation piers, under-construction, and overall dimensions are concerned, the three types are identical.

Standard Deister Plat-O Concentrating Tables are furnished in two different installation types; one for erectiondirectly on concrete piers, and the other on steel longitudinalmain channel frames. Further information will be gladlyfurnished upon request.

The Deister Plat-O Laboratory Concentrating Table is ideally suited for treating small quantities of ore in experimental plants and ore- testing laboratories, and for use as a pilot table in large plants. The 28 wide x 62 long deck, actuated by a halfsize Plat-O self-oiling head motion, will give results comparable to those that can be obtained with a full size table.This laboratory table is a simple, low cost, durably constructed unit incorporating the latest design features.

copper, manganese, zinc, and cadmium in tea leaves of different types and origin | springerlink

copper, manganese, zinc, and cadmium in tea leaves of different types and origin | springerlink

Concentrations of selected metals (Cu, Mn, Zn, Cd) in tea leaves were investigated. Samples included black, green, and other (red, white, yellow, and oolong) teas. They were purchased on a local market but they covered different countries of origin. Beverages like yerba mate, rooibos, and fruit teas were also included in the discussion. Metal determinations were performed using atomic absorption spectrometry. In black teas, Mn/Cd ratio was found to be significantly higher (48,09135,436) vs. green (21,31916,396) or other teas (15,6928393), while Cd concentration was lower (31.418.3g/kg) vs. other teas 67.0 (67.024.4). Moreover, Zn/Cu and Cu/Cd ratios were, respectively, lower (1.10.2 vs. 2.20.5) and higher (1086978 vs. 261128) when comparing black teas with other teas. Intake of each metal from drinking tea was estimated based on the extraction levels reported by other authors. Contributions to recommended daily intake for Cu, Mn, and Zn were estimated based on the recommendations of international authorities. Except for manganese, tea is not a major dietary source of the studied elements. From the total number of 27 samples, three have shown exceeded cadmium level, according to local regulations.

Tea is an infusion prepared from Camellia sinensis leaves originating from China and some parts of India. Nowadays, this evergreen shrub is grown in many other countries, such as Japan, Indonesia, Sri Lanka, Kenya, and Vietnam. The conditions of growing tea shrub, e.g., location, climate, and soil, have an impact on the taste and properties of the final beverage [1].

Tea is the one of the most popular beverages in the world. Six types of tea are distinguished as follows: green, white, yellow, oolong (blue tea/semi-fermented tea), red, and black. These types differ in terms of oxidation level, color of leaves, and infusion. The oxidation level of tea determines the color of leaves and infusion and it depends on the way the fermentation was carried out. The most popular types of tea are the following: green tea, which preserves the properties of fresh leaves to the highest degree, and black tea, which is obtained after full fermentation of fresh leaves.

Among other components, tea leaves consist of tanning agents, alkaloids, amino acids, pigments, and trace amounts of mineral compounds. Trace elements present in tea leaves play an important role in human metabolism [2]. They can be released from leaves to the infusion. Thus, tea leaves may become the source of metals in human diet. Some of the metallic elements, such as copper, manganese, and zinc are essential for basic processes in the human body while others (like cadmium) are toxic. The main aim of our study was to determine the content of copper, manganese, zinc, and cadmium in tea leaves and to find out if there are any significant differences among the teas of different types and countries of their origin.

Tea samples (n=27) were purchased on a local market in southern Poland. All samples were based on pure tea leaves, without additives or flavors. The set of samples included teas in the form of loose leaves as well as ground ones in tea bags. Samples were divided according to their type and country of origin. Among the samples, there were 12 samples of black tea, eight samples of green tea, two samples of red tea, two samples of white tea, two samples of oolong tea, and one sample of yellow tea. All details are given in Table 1.

Prior to the measurements, samples were dried for 2h at 105C. Moisture content (calculated from the mass difference prior to and after drying) varied between 3.5% and 8.4%. From each sample, approximately 0.5g was taken for the analysis, and microwave-assisted wet digestion with ultrapure nitric acid was carried out. Certified Reference Material (CRM No. 7, Tea Leaves, National Institute of Environmental Studies) was included in the analysis (two samples) in order to provide quality assurance.

All determinations were performed using a Perkin-Elmer 5100 ZL atomic absorption spectrometer. Cadmium was determined using electrothermal atomization, while the rest of the elements were determined using flame technique.

For samples divided into three groups, black teas, green teas, and the others, the descriptive statistics were calculated. The comparisons between groups were performed using the Kruskal-Wallis test with the Dunn post hoc test. Statistical calculations were carried out using commercially available packages Statistica v. 12.5 (StatSoft, Tulsa, USA) and GraphPad InStat v. 3.05 (GraphPad Software, La Jolla, USA).

Copper concentration in the samples varied from 9.10.2 to 32.70.4mg/kg (mean 18.76.3mg/kg). Street et al. [1] reported similar, though slightly higher values, between 9 and 65mg/kg (for the group of 30 samples). Similar results were obtained by Ashraf and Mian [3] as well as by Narin et al. [4]. In our study, the mean concentration of copper in black teas was determined to be 21.36.9mg/kg and for green teas 17.55.0mg/kg. These values were somewhat higher than those reported by Srividhya et al. [2] (14.340.49mg/kg for black teas and 11.280.08mg/kg for green ones, respectively) but, at the same time, lower than reported by Gajewska et al. [5] (black teas 31.311.2mg/kg; green teas 20.05.9mg/kg). The common point is, however, that both Srividhya et al. [2] and Gajewska et al. [5] found higher copper concentrations in black teas than in the green ones, which were also noticed in the present work. Among all types, the highest levels of copper were found in the red and black teas. Copper concentrations in white (15.50.1mg/kg) and oolong (9.150.07mg/kg) teas found in our study are similar to the results of other researchers (Marcos et al. [6], McKenzie et al. [7], Xie et al. [8]), although higher results also have been reported (Malik et al. [9] 17.631.6mg/kg for white and 15.125.8mg/kg for oolong tea). Copper content in red teas (22.00.7mg/kg) is comparable with the results of McKenzie et al. [7] (range 1543mg/kg).

Manganese concentration in the samples varied from 4574 to 221035mg/kg (meanSD 962388mg/kg). Similar results were published by Street et al. [1], where manganese concentration in 30 samples of different types of teas varied from 511 to 2220mg/kg. The authors did not notice a major difference between manganese concentration in black and green teas (nor they did for other elements: iron, zinc, and copper).

According to the type of the tea, the highest average concentration of manganese was observed for black teas (1094460mg/kg). This value is similar to the results from other studies [2, 5] which also have shown higher manganese concentration in black teas as compared to the green ones. According to Ashraf and Mian, Mn concentration in black tea samples studied by them was within the range of 4481072mg/kg [3], while in the study of Narin et al., this range was 5641082mg/kg [4]. Both these studies provided results with lower maximum values than the ones observed in our study. Interestingly, tea leaves from Kenya contained apparently the highest concentration of manganese (maximum of 2210mg/kg) among all countries of the samples origin. However, since only two samples from Kenya were analyzed, one should avoid making definite conclusions. Manganese concentration in white (106845mg/kg) and oolong (96826mg/kg) teas was similar to reported elsewhere (McKenzie et al. [7], Xie et al. [8]), although relatively low results can be found (Malik et al. [9] 293479mg/kg for white tea, which is, in general, low concentration, regardless of the type of tea). Manganese content in red teas (860183mg/kg) is comparable with the results of McKenzie et al. (range 6151268mg/kg) [7].

Zinc concentration in all samples varied between 12.60.2 and 45.50.1mg/kg. The mean value equaled 24.47.7mg/kg and was in line with the results reported by Srividhya et al., 25.390.59mg/kg for black teas and 26.390.92mg/kg for the green ones [2]. Results published by Street et al. were higher (21.575.2mg/kg) than in our study [1].

Our results of zinc concentration in green and black teas are similar to those reported by Srividhya et al. [2] as well as Gajewska et al. [5] and Narin et al. [4]. On the other hand, the mean value of zinc concentration in black teas given by Ashraf and Mian (65.731.3mg/kg) was much higher than the one found by us, which was (21.85.1mg/kg) [3]. In regard to white and oolong teas, zinc concentration found in our study (29.66.5mg/kg for white tea and 22.71.0mg/kg for oolong tea) are in line with other reports (McKenzie et al. [7], Xie et al. [8], Malik et al. [9]). Zinc content in red teas (38.77.7mg/kg) is comparable with the results of McKenzie et al. (range 2652mg/kg) [7].

The highest concentrations of zinc were found in red and yellow tea samples. When referring to the country of origin, the teas from China had the highest zinc concentration while tea samples from other countries (except for Japan) had similar levels of this element.

Average cadmium concentration in all tea samples equaled 4936g/kg. However, concentration of this element was rather disparate among all studied samples. The highest Cd concentration (1538g/kg) was found in sample no. 8green tea (tea bag), while the lowest one (6.00.8g/kg) in sample no. 10black tea (leaves). These results are much lower than results shown by Ashraf and Mian [3] and Narin et al. [4] who found Cd concentration in black teas to be equal 1.10.5 and 2.30.4mg/kg, respectively. Regarding oolong tea, our result (80.612.8g/kg) is very similar to the one presented by Marcos et al. (829g/kg; one sample only) [6].

Studies published by Gajewska et al. showed that an average Cd concentration was much higher for black teas (426506g/kg) than for the green ones (21843g/kg) [5]. Contrary to that, our results were in the opposite order; an average Cd concentration was 31.318.4g/kg for black teas and 60.352.8g/kg for the green ones. Therefore, not only was the tendency reversed, but also the values apparently differed. However, more recently, Srividhya et al. reported Cd concentration in green teas to be twice as high as for the black teas (1.590.26 and 0.890.10mg/kg, respectively), though this result is based on two samples only [2].

Among the tea samples studied by us, the lowest concentration of cadmium was found in black teas and the highest in red and oolong teas. When considering the country of origin, low Cd concentrations were found in teas from Japan and Indonesia while in the sample from Taiwan, it was relatively high. Table 5 shows comparison of our results with other researches.

Comparing black and green teas, Mn/Cd ratio was found to be significantly different between these two groups. When comparing black teas to the others, four parameters showed significant differences: Cd concentrations, Mn/Cd, Zn/Cu, and Cu/Cd ratios. Further studies, including more tea samples, are needed to establish if there is such a general trend for these groups of teas.

Since black tea undergoes full fermentation during production, it seems that this process can affect the content of the metals (e.g., removing the metals by rinsing them out from the leaves; the degree of this removal can vary for each metal). Besides this, the content of the given metal in tea leaves obviously depends on its content in the tea plantation soil.

Daily intake of all determined metals with consumed tea infusion for black and green teas was estimated. It was based on the assumptions that the daily consumption of tea is three cups and each one is prepared using 1.5g of tea leaves. Extraction degrees for each element were taken from the report of Gajewska et al. [5]. Recommended daily intake for Mn, Zn, and Cu was taken from the Dietary Reference Intakes [10]. In addition, the European Union Population Reference Intake for adults is given for comparison [11].

Estimated daily intakes together with the recommendations mentioned above for black and green tea are listed in Table 6. It can be noticed that tea is a major source of manganese in the diet, while intake of other elements is negligible.

Since cadmium is considered a toxic element, there is no RDI defined for it. Cadmium content in the samples can be compared with the upper allowed level of this element in tea, which was established by ordinance of the Health Minister of Poland [12] and equals 0.10mg/kg of dry material. It can be noticed from Table 3 that only in three samples (denoted 7, 8, and 24) was this level exceeded.

In separate studies, other types of tea, and similar beverages, were examined. Schunk et al. [13] analyzed Brazilian herbal teas (chamomile, lemongrass, fennel, and yerba mate). In that report, the copper concentration varied from 0.190.05 to 0.430.07g/g while the levels of cadmium were much lowerbetween 0.030.01 and 0.050.01g/g. The highest Mn concentration was found to be 53.457.07g/g. Results for copper and cadmium overlapped with those obtained in our work, but the content of manganese was much lower.

Rusinek-Prystupa et al. [14] examined teas containing yerba mate and rooibos. For both these groups, the concentration of Zn varied from 7.19 to 106mg/kg and concentration of Cu was in a range from 1.98 to 14.05mg/kg (being much lower for rooibos than for yerba mate). These values are in line with our results, with copper content being somewhat lower in rooibos than in ordinary tea. Manganese in yerba mate was present in the concentration from 269 to 2261mg/kg which is again similar to the results of this work for green and black tea. However, the values found in rooibos were much lower (1.9803.363mg/kg).

Brzezicha-Cirocka et al. [15] analyzed eight types of fruit teas. Among all these groups, the concentrations were in a range of 1530mg/kg for Cu, 130770mg/kg for Mn, and 3.815mg/kg for Zn. These values are, in general, comparable with those found by us in green or black teas (with our results being slightly higher).

Currently, a large selection of white and red teas is available on the Polish market. Their lower consumption is implicated not only by their relatively higher prices but also by the nutritional habits of Polish consumers. On the other hand, it is well known that white teas have rich chemical composition (including the highest polyphenol content among all teas and therefore strong antioxidant activity). Similarly, it is believed that red teas also exert a variety of biological functions. For this reason, it is important to examine such teas, paying special attention to trace elements as well as other ingredients with favorable properties in human dietin order to convince consumers to drink them more often. Small number of such teas examined in our study is its limitation and deserves next research particularly focused on white and red teas as possible candidates for potent functional food.

In black teas, Mn/Cd ratio was found to be significantly higher vs. green or other teas, while Cd concentration was lower vs. other teas. Moreover, Zn/Cu and Cu/Cd ratios were, respectively, lower and higher when comparing black teas with other teas. This differentiation can be caused by the fermentation process during black tea production. Our results partly agree with the reports of other researchers; however, some differences can be noticed. In particular, zinc content in black tea as well as cadmium content in black and green teas was found to be much lower than reported by other authors. Very high content of manganese in two samples of black teas from Kenya was observed. Tea is a major dietary source of manganese while the intake of other elements is negligible. In three samples, content of cadmium was found to be higher than allowed by regulations of the Health Minister of Poland.

Food and Nutrition Board, Institute of Medicine (2001) Intakes for vitamin A, vitamin K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc. National Academy Press, Washington, D.C.

Nutrient and energy intakes for the European Community. Reports of the Scientific Committee for Food (1993) Thirty-first series. Published by the Commission of the European Communities,Directorate-General Telecommunications, Information Industries and Innovation,Luxembourg. Pp. 193-214

Health Minister of Poland (2003) Ordinance of Health Minister of Poland regarding the maximum levels of chemical and biological contaminants which can be found in food, food components, permitted additives, reprocessing-auxiliary additives or on the surface of food.Dz.U. [Journal of Laws] from 2003, No. 37, item 326:2415

Schunk FPT, Kalil IC, Pimentel-Schmitt EF, Lenz D, De Andrade TU (2016) ICP-OES and micronucleus test to evaluate heavy metal contamination in commercially available Brazilian herbal teas. Biol Trace Elem Res 172:258265

Rusinek-Prystupa E, Marzec Z, Sembratowicz I, Samoliska W, Kiczorowska B, Kwiecie M (2016) Content of selected minerals and active ingredients in teas containing yerba mate and rooibos. Biol Trace Elem Res 172:266275

Brzezicha-Cirocka J, Grembecka M, Jezusek M, Szefer P (2015) Ocena zawartoci wybranych mikropierwiastkw w herbatach owocowych [Evaluation of consumption of microelements in popular fruit teas]. Bromat Chem Toksykol 48:274277

Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Podwika, W., Kleszcz, K., Kroniak, M. et al. Copper, Manganese, Zinc, and Cadmium in Tea Leaves of Different Types and Origin. Biol Trace Elem Res 183, 389395 (2018). https://doi.org/10.1007/s12011-017-1140-x

progress, challenges, and perspectives of bioleaching for recovering heavy metals from mine tailings

progress, challenges, and perspectives of bioleaching for recovering heavy metals from mine tailings

Xiufang Gao, Li Jiang, Yilin Mao, Bin Yao, Peihua Jiang, "Progress, Challenges, and Perspectives of Bioleaching for Recovering Heavy Metals from Mine Tailings", Adsorption Science & Technology, vol. 2021, Article ID 9941979, 13 pages, 2021. https://doi.org/10.1155/2021/9941979

The accumulation of mine tailings on Earth is a serious environmental challenge. The importance for the recovery of heavy metals, together with the economic benefits of precious and base metals, is a strong incentive to develop sustainable methods to recover metals from tailings. Currently, researchers are attempting to improve the efficiency of metal recovery from tailings using bioleaching, a more sustainable method compared to traditional methods. In this work, the research status of using biological leaching technologies to recover heavy metals from tailings was reviewed. Furthermore, CiteSpace 5.7.R2 was used to visually analyze the keywords of relevant studies on biological leaching of tailings to intuitively establish the current research hotspots. We found that current research has made recent progress on influencing factors and microbial genetic data, and innovations have also been made regarding the improvement of the rate of metal leaching by biological leaching combined with other technologies. This is of great significance for the development of bioleaching technologies and industrial production of heavy metals in tailings. Finally, challenges and opportunities for bioleaching provide directions for further research by the scientific community.

Rapid social and industrial developments have resulted in an increased demand for metals. As a result of rapid industrial development combined with increased exploitation of large quantities of mine resources, the environmental pollution of tailings is expanding at an alarming rate. The environmental impacts of tailings will eventually directly or indirectly threaten the human health (Figure 1). In soil and sediment, chemical pollutants caused by human activities have accumulated over 2,000 years. An early example of such pollution is heavy-metal mining waste. The environmental challenges posed by huge volumes of tailings and tailings dumps are often overshadowed by the economic benefits of mining. Tailings contain harmful quantities of toxic substances that can potentially pose serious health and environmental problems through air dispersion of air-dried tailings, leaching of potentially toxic chemical species, erosion and uptake by the aquatic system, and bioaccumulation [1].

Heavy metal contamination from tailings is detrimental to the human and environmental health [2]. The Luhun Reservoir, Henan Province, China, is located downstream of a molybdenum mining area. A recent study assessing the pollution of the reservoir found that molybdenum was the main pollutant in the overlying water of the reservoir, with the single element pollution factor () of molybdenum which is the highest among all heavy metals, at a mean value of 2.05 [3]. Similarly, there are a large number of gold mine tailings in the Welkom and Virginia areas of the Free State Province in South Africa. According to the World Health Organization and the South African National Drinking Water Standard, an analysis of the groundwater quality in the target area found that 40% of the analyzed samples contained lead exceeding the drinking water quality standard limit, 63% contained iron exceeding the standard limit, 100% contained faecal coliform bacterial counts noncompliant with the current guidelines, and 50% contained E. coli counts exceeding the standard limit [4]. Because groundwater is the main source of drinking water for the local population, this pollution poses a serious threat to their health. Furthermore, environmental pollution indirectly harms other organisms. In the city of Vicosa do Ceara/CE in northeastern Brazil, Fabio et al. (2021) assessed the impact of an abandoned copper mine on the environmental quality of the ecosystem through a comprehensive ecological and biogeochemical analysis. Their results showed that there was still a large amount of copper in the waste rock of the abandoned copper mine after 30 years of weathering, and drainage from the mine significantly reduced the aquatic macroinvertebrates and increased the copper content in living organisms [5].

Heavy metal pollution from tailings also seriously damages local land resources. Heavy metal mining and processing activities in southern Poland led to heavy zinc pollution and moderate lead pollution of the local agricultural land and thus agricultural production in these areas; as a result, the planting of green leafy vegetables was banned, which has led to significant economic losses [6].

As discussed above, the environmental risks of heavy metals from mining are very severe. However, tailings are also an important secondary resource. Gold, silver, lead, zinc, sulphur, indium, gallium, cadmium, germanium, selenium, tellurium, and other associated elements recovered from Chinese copper ore during the processing and smelting process account for 44% of the total output value of the raw materials; associated gold accounts for more than 35% of Chinas gold reserves, of which 76% of gold and 32.5% of silver is produced by copper mines [7]. Moreover, rare earth elements are essential components of high-tech electronic and electrical materials, and reserves of natural rare earth elements are limited worldwide, except in China [8]. However, many mine tailings are rich in mineral-associated rare earth elements, and such tailings are thus an important source. Therefore, in order to solve the shortage of metal resources and the problem of tailing pollution, suitable, effective, and economical technologies are needed for recovery and removal of heavy metals from mine tailings [9].

Fortunately, various methods have been developed in recent years to recycle tailings, including the promising technique of bioleaching, chemical extraction remediation techniques, and electrochemical repair techniques, that convert waste into value. Chemical extraction is limited by soil complexity and extractants. Electrochemical repair techniques are expensive and require complex operations. However, bioleaching is a low-cost, green technology for leaching metals from a variety of minerals and waste materials [10]. In the early 1950s, Colmer was the first to extract copper from a mine dump at the Kennecott Copper Corporation using microorganisms [11]. Thus, bioleaching technology opened the era of microbial metallurgy. Biological leaching refers to the direct action of some microorganisms in nature or the indirect action of their metabolites to produce oxidation, reduction, complexation, adsorption, or dissolution, by which processes certain insoluble components (such as heavy metals and other metals) are separated from the solid phase. The microorganisms used in biological leaching are mainly eosinophilic, inorganic autotrophic bacteria. Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, and Leptospirillum ferrooxidans are the most widely used. Currently, most minerals and ores are processed at the industrial scale using bioleaching [12]. For example, approximately 2025% of the worlds total copper are produced using bioleaching [13]. However, biological leaching technology has its limitations, such as the microbial leaching efficiency and reaction cycle.

Advances in molecular biology techniques and their applications in biosynthesis to detect and identify organisms have expanded our understanding of the interactions of metallic microbes and their important role in metal extraction and recovery [14]. This provides a good impetus for the industrial application of heavy metals from biological leaching of tailings.

This review provides an overview of the mechanisms and influencing factors of bioleaching technologies and provides a general understanding of the current status of the bioleaching of copper, iron, and zinc tailings, rare earth elements, and four toxic metals. The challenges and opportunities for the recovery of heavy metals from tailings by biological leaching are also discussed, which will provide a valuable reference for the full exploitation and utilization of secondary resources and the industrial development of the recovery of heavy metals from tailings using biological leaching technologies.

The essence of the biological leaching process is that Thiobacillus acquires the energy needed for growth by oxidizing reduced sulphur compounds, which leads to a decrease in the pH value and changes in the redox environment of the environmental system, thus changing the state of the heavy metals in the system from the original organic matter-bound state to the free state. Since the early 1950s, Fe/S-oxidizing bacteria have been used in industrial-scale processes to extract metals from sulphide ores [11]. The first isolated and most widely studied Fe/S-oxidizing bacteria are A. ferrooxidans; therefore, most of the research on the mechanism of bioleaching has been limited to the behavior of A. ferrooxidans in the bioleaching of sulphide minerals [15]. The mechanisms of bioleaching of sulphide ore by A. ferrooxidans are divided into direct and indirect mechanisms.

Direct mechanisms: the microorganisms oxidize sulphide minerals through direct attack on the mineral surface [16] and possibly by the cells unique oxidase system that directly oxidizes sulphide minerals. Hydrogen ions are produced simultaneously, resulting in a decrease in the pH of the environmental system and an increase in the redox potential and thus the formation of soluble sulphates [17]. However, it is difficult to distinguish between the bacterial cell wall and the molecular film of sulphide; therefore, this mechanism is more suitable for contact leaching [18]. This can be expressed in terms of the following reaction equation (1):

Indirect mechanisms: metabolites of Fe/S-oxidizing bacteria are used in redox reactions that occur with sulphide minerals, and finally, a redox circulatory system is formed. The sulfuric acid produced reduces the pH of the environmental system to approximately 2.0 and greatly promotes the dissolution of heavy metals [19]. Indirect mechanisms can be summarized by the following reaction equation (2) (taking pyrite as an example):

Another approach is to complement the indirect mechanism by characteristics of bacterial attachment to mineral surfaces, in which the attached cells oxidize ferrous ions into iron ions within a layer of bacteria and extracellular polymeric substances, and the ferric ions within this layer leach the sulphide [20].

In summary, all previous studies have found that the key to the exploration of the mechanism of biological leaching lies in microorganisms. Only by thoroughly studying the behavior of microorganisms in the leaching process can the mechanism of biological leaching be accurately and systematically interpreted, which will also depend on developments in molecular biology and other disciplines.

Bioremediation technology has attracted increasing attention in the field of environmental protection. At its core, the mechanism and species selection of microorganisms in pollution remediation have become the focus of research. In bioleaching, bacteria play a catalytic role [18], which is key to the industrialization of recovering heavy metals from tailings by biological leaching. Using microorganisms to extract heavy metals from tailings is more ecologically friendly, which not only controls tailings pollution but also alleviates the shortage of primary resources and will not produce harmful gases to form secondary pollution during the entire reaction process. A. ferrooxidans, A. thiooxidans, and L. ferrooxidans are the most commonly used microorganisms in bioleaching of heavy metals from tailings. Their physicochemical properties are presented in Table 1. As for energy sources, A. ferrooxidans, A. thiooxidans, and L. ferrooxidans get their energy from iron, sulphur, and iron, respectively.

Regarding the selection of microbial species, natural microorganisms (indigenous microorganisms) show better adaptability and have a higher leaching rate; therefore, the majority of studies to date used indigenous microbes [21, 22]. For example, indigenous bacteria can mediate electrochemical morphology and thus significantly improve arsenic leaching from tailings; thus, without effective treatment of arsenic-containing tailings, enhanced arsenic migration by indigenous bacteria will increase the risk of environmental contamination [23].

In terms of the selection of microbial diversity, mixed bacteria leaching is more efficient, and the majority of studies to date focused on the use of mixed bacteria leaching [24, 25]. In a study of bioleaching of heavy metals from copper and silver mine tailings in the Philippines, the microbe cultures used were single bacterial and mixed cultures, respectively. The results showed that the leaching rate of copper and arsenic of the mixed bacteria was higher than that of the single bacteria, and the single bacteria and the mixed bacteria mediated the occurrence pattern of heavy metals in different ways [26]. Due to the synergistic effect of mixed bacteria, higher bacterial concentrations and copper extraction rates could be obtained in the biological leaching, and the highest copper extraction rate of mixed bacteria (73.7%) was significantly higher than that of any single bacterial culture [27]. One study proposed that the highest bioleaching rate of valuable metals could be obtained using a natural consortium of drainage water combined with iron-oxidizing L. ferrooxidans Teg [28].

The whole process of biological leaching can be summarized from the aspects of microbial species, diversity, bacterial density, activity, and distribution as follows [2931]: Biological leaching is a continuous reaction process, and the best microorganisms are selected according to the characteristics of these processes; generally, mixed strains and indigenous strains have high leaching rates, and the higher the number and activity of microorganisms, the higher the leaching rate; microorganisms are uniformly distributed in stirred tank reactors, but not in leaching heaps, which are one of the reasons why the industrial application of biological leaching of heavy metals from tailings is limited.

In the future, the microorganism selection related to bioleaching needs to be further improved in several aspects [32]: (1) seeking a microorganism that can achieve oxidation reactions in alkaline environments is conducive to the extraction of alkaline minerals, and the application of biological leaching could be expanded; (2) to strengthen the tracking of microbial morphology and species changes before and after leaching, to better explore the microbial mechanism and improve leaching efficiency [33]; and (3) identification and development of chlorine-tolerant organisms can promote the utilization of seawater or brackish water in bioleaching, reduce the cost, and at the same time benefit the reality of freshwater resource shortages.

Biological leaching methods for the treatment of electronic waste can be divided into three types according to the type of biomass exposure to the waste: one-step, two-step, and spent-medium [34]. In the study of biological leaching of heavy metals from tailings, the operation steps are generally as follows (Figure 2): first, the tailing samples are collected and treated, and physical and chemical analyses are carried out; second, the bacterial strains are screened and identified, enriched in a sterile environment, and the bacterial solution is preacidified; finally, a certain amount of tailing sample and bacterium fluid is placed in a 250mL conical flask, the blank control group is set up, and all conical flasks are placed in a constant temperature oscillating shaker at an appropriate temperature for the bioleaching experiment. The specific experimental conditions are selected according to the species and mineral types. Any evaporated water in the experiment is replenished with ultra-pure water, and the pH and redox potentials are measured daily. Furthermore, the supernatant is collected daily to analyze the heavy metal content in the solution. All instruments used in the experiment should be sterilized by such techniques as high-temperature sterilization, adding sodium azide, etc.

The pH is an important physical and chemical parameter in biological leaching. In the study of bioleaching of heavy metals from tailings, iron/sulfur-oxidizing bacteria are more likely to undergo redox reactions under acidic conditions. The effect of pH on the optimum leaching rates of different metals is different. In one study, when the slag particle size was less than 0.83mm, the smelting slag of lead/zinc on copper, iron, lead, zinc, and other metals was highly dependent on pH, but the pH had little influence on the solubilization of manganese [35]. Before the bioleaching reaction took place, the pH of the bacterial solution was adjusted to reach the optimum pH range for the microorganisms. During the reaction, the change in pH will affect the microbial activity and thus the metal leaching rate; therefore, it is very important to monitor the change in pH during the reaction. One study found that preacidification treatment was needed to ensure the leaching rate of heavy metals [36], but not all biological leaching experiments need preacidification treatment, and another study found that when there was no preacidification treatment, the addition of an right amount of substrate impart a buffering action to make the pH of the reactor more stable and gradually decreased [37].

A different study showed that the reduction potential of the solution had a great influence on the leaching rate of pyrite, and the influence degree was much greater than the number and activity of bacterial cells [38]. A high oxidation-reduction potential (ORP) reflects high biomass concentration, and the bioleached chalcopyrite was controlled by ORP under high pH [39].

Temperature is one of the important influencing factors in the process of bioleaching. It mainly affects the microbial activity during the process of biological leaching, which then affects the leaching of heavy metals from tailings. Experiments were carried out to examine the effect of temperature on heavy metal leaching in the temperature range of 742C, in which the growth rate of acidophilic bacteria varied with pH, but the degree of change depended on the temperature [40]. Maintaining a constant temperature during large-scale operations is also a problem to be considered in the industrialization process of bioleaching of heavy metals from tailings.

Previous studies on pulp density are scarce, but current studies show that pulp density mainly affects the leaching of heavy metals by affecting the pH. The larger the pulp density, the greater the pH decline [9]. The effects of mineral pulp densities of 5, 10, and 30g/L on bacterial activity for different bacteria were investigated in a batch reactor. For A. thiooxidans, the higher the pulp density, the higher the pH, while for P. putida, the change in pulp density had no effect on the pH [41]. Because a high pulp density significantly inhibits microbial activity, when the pulp density was greater than 15%, it had a great influence on the leaching rate of copper and zinc [35, 42].

A continuous oxygen supply is required during biological leaching. The oxygen and carbon dioxide contents are closely related to the activity of the microorganisms and affect the progress of the redox reaction. The monitoring of dissolved oxygen showed that the demand for oxygen increases with an increase in pulp density [43]. An empirical model of dimensionless parameters showed that biological leaching of manganese minerals by heterotrophic microorganisms occurred only under oxygen-limiting conditions [44]. The use of a higher dissolved oxygen concentration (above 4.1mg/L) inhibits the oxidation rate of ferrous ions. The optimal carbon dioxide concentration of ferrous oxidation ranges between 7 and 17% (V/V), and the oxidation rate of iron is severely limited when the carbon dioxide concentration is lower than 7% [45].

In addition to the above common factors, there are the following new findings. For example, the leaching rate of heavy metals from tailings decreases with an increase in the solid concentration [46]. Furthermore, the activity of acidophilic bacteria in a stirred tank reactor under high pressure was studied for the first time, and the bacteria were found to remain active at a low oxygen partial pressure of +40bar [47]. In a different study, ore particles of similar particle size fractions but different amounts of microcracks were prepared to investigate the influence of microcracks on bacterial activity, and the results showed that a larger number of microcracks were beneficial to bacterial growth and increased the bioleaching efficiency of copper by about 12.2% [48]. The effect of salinity was also investigated, and it was shown that low levels of salinity (5g/L sodium chloride) have a positive effect on the bioleaching efficiency [49]. These new influencing factors are also important limiting conditions for the industrial production of heavy metals from biological leaching of mine tailings. Continuous research should be carried out to determine the optimal conditions for each factor to obtain the best metal leaching rate.

CiteSpace (5.7.R2) provides data visualization and network analysis capabilities [50]. Based on co-authors, cowords, and cluster analysis functions, CiteSpace can point out new trends and hot topics in a research area [51]. CiteSpace (5.7.R2) was used to analyze the research hotspots of bioleaching technologies with high objectivity of the results in this study. The core collection database of Web of Science was selected for basic retrieval. The retrieval topics were bioleaching and tailings, and a total of 157 records were retrieved. All data were exported, and CiteSpace was used for the visual analysis of keyword co-occurrence (Figure 3). Nodes in the graph shown in Figure 3 represent keywords, edges represent the relationship between keywords, and circles represent the frequency of keywords. The main keywords shown are bioleaching, iron, heavy metals, Acidithiobacillus ferrooxidans, bacteria, extraction, and copper and are thus the current research hotspots. Table 3 shows the count, centrality, and earliest occurrence year of the keywords (arranged by frequency size).

Subsequently, a cluster analysis was conducted by selecting the label clusters with the indexing term function (Figure 4). On the resulting scale from 0 to 5, the smaller the number, the more keywords are included in the cluster. The results showed that biocyanidation is the keyword with the largest storage capacity, and thus related research on this hot spot will be discussed below.

Copper was one of the first metals used by humans. Today, it is the most commonly used material for cables, electronics, electrical components, and construction; therefore, the demand for copper will continue to grow. Primary resources have been overexploited, and for sustainable development of resources, the development and utilization of tailings have become urgent. A survey of the copper content in tailings of the Musina mine, an abandoned copper mine in the northern Limpopo Province, showed that the residual copper currently stands at 8,555 tons [52]. As ore grades continue to decline, the byproducts of foam flotation are expected to produce copper tailings that still contain large amounts of unrecovered copper [53]. The tailings of Serbian copper ore were biologically leached with thermophilic acidophilus bacteria at 40C, and the best copper leaching rate obtained was 84% [54]. Analysis of copper ore obtained from the new base of Qarashoshaq in northern Zhylandy (Kazakhstan) showed that the highest extraction rate of copper was 95% by biological leaching and 66.8% by chemical leaching, indicating that the leaching rate of copper was higher for biological leaching [55]. At present, the biological leaching of oxide ores has not been thoroughly studied; however, Pseudomonas aeruginosa, a heterotrophic bacterium, has been used for biological leaching of copper oxide ores and zinc oxide ores, and 47% and 41% of copper and zinc were extracted, respectively [56]. Although the mechanism of combined leaching needs to be studied further, the recovery rate of copper under alkaline conditions was significantly improved when ammonia solution, and new alkaline bacteria were used [57]. In a study on the effect of magnetic induction intensity on the leaching rate of heavy metals, it was shown that the leaching rate of copper and arsenic increased with the increase of magnetic induction intensity, and when the magnetic induction intensity was 11mT, the metal leaching rate reached the best [58].

Metallic zinc is not only an irreplaceable material for batteries but also an essential trace element for the human body. Zinc resources mainly exist in the form of lead-zinc ore; thus, it is necessary to recover zinc from secondary resources. The potentially high mobilization and dispersion of zinc found in mine tailings in central Mexico can potentially harm the surrounding ecosystem [59]. Therefore, using bioleaching to recover zinc from tailings would solve two problems with one action. The zinc leaching rate was found to increase with an increase in temperature, reaching 96.96% at a temperature of 39.85C; based on Arrheniuss law of thermodynamics, the activation energy of the zinc bioleaching reaction was 39.557kJ/mol [60]. Moreover, the leaching rate of zinc was found to vary depending on the bacterial species and bacterial diversity. Analysis on an ore sample from a gold mine in northeastern Thailand showed a leaching rate of zinc that was six times higher with acidic thiobacillus ferric oxide as the microorganism than without the microorganism [61]. The tailings dam of the Kooshk lead-zinc mine was found to contain approximately 3.64% zinc, and more than 90% of sphalerite was leached within 14 days using mixed bacteria, but only 44% of zinc was extracted without bacteria [62]. In a study on the extraction of zinc from low-grade zinc concentrate by biological leaching, the results showed that the leaching rate of zinc was increased by 36% by thermophilic bacteria [63]. Yet, another study showed that the addition of starch and shredded newspaper increased the zinc bioleaching rate. In the presence of shredded newspaper and starch, the zinc leaching rates were 88% and 95%, respectively, and the bioleaching time was reduced from 18 days to 10 days and 13 days, respectively [64].

Nickel was used as an excellent iron material in the early days. To control nickel tailing pollution, legume trees were planted on nickel tailings in the tropical area of Zimbabwe. After 20 and 40 years of restoration, different degrees of fertility islands were formed under the canopy of the legume plants [65]. A study of the bioleaching of tailings from the Tram Heap leaching plant in Finland found that some of the nickel dissolved in the primary heap reprecipitated and was retained in secondary ore, indicating that the nickel release was very rapid compared with abiotic experiments [66]. Biological leaching experiments were also carried out on ore samples of Brazilian nickel iron ore using a Bacillus subtilis strain. After 7 days, approximately 8.1% Ni (0.7mg Ni/g ore) was extracted. Meanwhile, pretreatment with microwave heating increased the biological extraction rate of nickel from 8% to 26% (2.3mg Ni/g ore) [67]. A study analyzing pyrite and bentonite showed that, based on mineralogical characteristics, Ni is locked in pyrite and bentonite, and nickel leaching is thus related to the solubility of pyrite and bentonite; comparison of the leaching rate of nickel under aerobic and anoxic conditions at a pH of 1.5 showed that the optimal nickel leaching rate was obtained under aerobic conditions [68]. The bioleaching recovery of nickel from low-grade nickel-copper sulphide tailings was found to be as high as 91.5%; furthermore, the nickel in the leaching mixture obtained by precipitation of sodium ettringite was enriched in the form of sulphide precipitation with a metal content of 8% [69]. However, the industrial application of bioleaching sulphide ores has made little progress. A new study showed that aerobic reductive dissolution (AeRD) using an A. thiooxidans and A. ferrooxidans consortium was able to extract 5357% of nickel in just 7 days; this method not only uses less acid, thus reducing processing costs, but also includes a process of aerobic acid regeneration [70].

The contents of rare earth elements in minerals are not as high as those of copper, zinc, iron, and other metals, but the unique optic, catalytic, electronic, and magnetic properties of rare earth elements make them invaluable in a number of advanced technological fields, especially their thermal stability, good electrical conductivity, and corrosion resistance [71]. With the rapid industrialization and modernization, technologies that rely heavily on rare earth elements, such as autocatalysts, rare earth magnets, rechargeable batteries, screens, hybrid cars, and low-energy lighting, are also developing rapidly, and the resources of rare earth elements have become insufficient [72]. While the development of secondary resources is a concern, so are the limitations of recycling technologies. Currently, many recycling technologies are based on biological leaching, continuous improvement, and innovation.

China has the worlds largest rare earth element reserves by the mining value. In terms of global production, China (85%) dominates, followed by Australia (10%), Russia (2%), India (1%), Brazil (1%), Malaysia, and Vietnam [73]. Rare earth elements play important roles in industry, medicine, military, and agriculture, and the consumption of rare earth element resources is very large worldwide; so, they have a certain economic value. According to the European Union and the US Department of Energy, a shortage of rare earth elements would have serious adverse economic effects [74]. The current rare earth element recovery research mostly focuses on electronic waste; however, some rare earth elements coexist with other minerals, and thus tailings will also become an important source of rare earth elements. Rare earth elements are commonly found in tungsten carbide, monazite, xenon ore, and recently adsorbed ion clays; therefore, acidic or alkaline recovery routes are required [75, 76]. Both autotrophic and heterotrophic microorganisms can be used to leach rare earth elements [77, 78]. In particular, Pseudomonas, Enterobacter, Serratia, and Bacillus have remarkable rare earth element recovery abilities in monazite ores [79, 80]. In one study, different strain types and growth media were used to extract rare earth elements from rare earth element ore in China, and the results showed that the leaching efficiency of Streptomyces sp. FXJ1.172 was the highest, and the bioleaching efficiency of rare earth elements was improved by maximizing the carrier and acidity of real iron [81]. In addition to the selection of microorganisms, changes in the leaching conditions can also result in different leaching rates. Various rare earth elements can also be recovered effectively by using a high Eh and low pH leaching solution [82]. Bauxite contains complex and diverse rare earth elements, and organic acid bioleaching, reductive bioleaching, and oxidizing bioleaching were used in one study to recover its rare earth element content; the final recovery rate for the rare earth elements from neodymium to gadolinium was the highest, and the leaching rate of single rare earth elements ranged between 26.2% and 62.8% [83]. Furthermore, rare earth elements are also present in coal combustion residual fly ash and in one study were extracted from fly ash by Candida bombicola, Phanerochaete Chrysosporium, and Cryptococcus curvatus [84].

Biological leaching of precious metals occurs mainly through complexation and decomposition mechanisms of cyanogenic bacteria [85]. A pulp density of 20% (W/V) can result in a gold leaching rate of approximately 95%, and the recovery of gold after biological oxidation can be as high as 95.7% [86]. Precious metals are often lost in tailings owing to encapsulation of the precious metal particles in the ores. To solve this problem, tailing samples are pretreated by biological leaching before cyanide leaching, which has increased the leaching rate of gold to 95% and the leaching rate of silver to over 98% [87]. However, cyanide is toxic and poses environmental risks. In order to mitigate these risks, leaching methods using thiosulfate or halogen compounds instead of cyanide have been developed, and dump or heap bioleaching technologies also have a certain commercialization prospect [88]. Using an initial bacterial oxidation process, one study improved the leaching rate of gold from flotation tailings through biochemical leaching; 72% gold was extracted, 7% more than through the expensive sodium peroxide method, and 10% more than through the traditional cyanidation method [89]. Based on the latest literature, the recovery of gold from minerals is no longer achieved through the use of bioleaching technologies only, but through a combination with oxidation of microorganisms or the addition of new leaching agents in the bioleaching technologies, which greatly increases the recovery rate of gold. Further research will lead to the formation of a combined leaching method that is environmentally friendly and has a high leaching rate.

Similar to gold, silver has very little associated content, and biological leaching alone does not yield good leaching results. The silver tailings in Coahuila, Mexico, contain a large amount of silver mining waste, and the leaching efficiency of silver was found to be 4067% using indigenous microbial leaching [90]. Lead and zinc tailings contain small amounts of valuable metals. To make full use of this secondary resource, high-temperature roasting combined with biological leaching was used to recover silver. At 900C, the leaching rate of silver reached 84.39%, and the recovery amount of the leaching solution was 9.98mg/L [91]. In a recent study, a pyrite-enhanced chlorination roasting technology achieved optimal gold and silver recoveries of 98.56% and 87.92%, respectively, and reduced the emission of harmful gases compared with other additives [92]. The latest research results show that the recovery of silver has improved through the application of innovative technologies such as high-temperature roasting and chlorinated roasting of pyrite.

Uranium is radioactive, has a very long half-life, and is mainly used as nuclear fuel. Uranium resources are mainly distributed in the United States, Canada, and South Africa. Although large amounts of uranium exist in the Earths crust, it is difficult to exploit these reserves due to technical limitations. However, uranium metal is an important raw material in nuclear physics, and primary uranium mineral resources have been overexploited. Thus, future exploration will be focused on the secondary recovery of waste resources such as tailings. The recovery of uranium from ores and tailings using bioleaching technologies would exceed the economic value of underground mining [93]. The current maximum leaching rate (69%) was achieved within 60 days in a large column bioleaching experiment of 100kg and 2t from an Indian uranium mine [94]. A summary of recent studies indicates that uranium ore is mainly treated by stacking, heap leaching, stope, and in situ biological leaching. Because uranium deposits contain rare earth elements, future bioleaching applications are likely to focus increasingly on these deposits, allowing for the full exploitation of metallic resources [93, 95].

Lead, chromium, and arsenic are toxic heavy metal pollutants. In the past, due to a lack of regulation and environmental protection consciousness, tailings piled up at random and caused widespread pollution of these metals, triggered a wide range of endemic diseases, thus posing a serious threat to human health. Today, pollution control of tailings is therefore mainly focused on these three metals.

In a study of lead concentrations in a 300-year-old abandoned mine tailings dam in Zacatecas, Mexico, the average level of lead was found to be mg/kg, significantly above international standards, with a risk of contamination mobility and possible inclusion in the food chain [96]. Lead can be recovered effectively from tailings using improved bioleaching technologies. Increasing the salt concentration and temperature can promote the recovery of lead; therefore, biological leaching combined with brine leaching can remove lead from lead and zinc tailings. Using only biological leaching under the best conditions to recover lead yielded 4.12% lead, while the addition of sodium chloride at a concentration of 150g/L to the biological leaching residues at 25C recovered 94.70% of lead and at 50C as much as 99.46% [97].

Treatments of chromium have mainly been developed to reduce hexavalent chromium to trivalent chromium, or to prevent the oxidation of trivalent chromium. Oxides of hexavalent chromium do not degrade by themselves and will accumulate in organisms for a long time. The industrial wastewater standard defines hexavalent chromium as a first-class pollutant, and many countries even prohibit products of hexavalent chromium electroplating from entering the market. The treatment of chromium pollution in tailings using bioleaching technologies is constantly being updated. Chromium-containing tailings are abundant in the Sukinda Valley, India. In a study on bioleaching of chromium, during the bioleaching process, the total chromium was initially extracted in the form of hexavalent chromium due to phosphate in the medium and was subsequently reduced due to hexavalent chromium adsorption and reduction to trivalent chromium [41].

An investigation of the metal content in agricultural soil near abandoned metal mines revealed that arsenic has a more profound impact on agricultural soil than the migration behavior of cadmium, lead, and zinc; therefore, the recovery of arsenic from tailings is crucial [98]. Experiments using the GEOCOAT technology to remove arsenic from arsenic-rich tailings showed a column bioleaching rate of more than 95% and no effect of temperature on the arsenic leaching rate [99]. The biological leaching of arsenic from high-concentration arsenic tailings by A. ferrooxidans was found to be mainly affected by the pulp density and pH. When the initial pH was changed from 2.0 to 2.2, the leaching rate decreased by 45%, and when the pulp density increased from 2.0% to 4.0%, the leaching rate decreased by 55%; thus, the pH range should be controlled, and the appropriate pulp density should be selected when leaching high-concentration arsenic tailings [100]. In another biological leaching study of arsenic from tailings with the high arsenic content (approximately 34,000mg/kg), the leaching rate was mainly influenced by temperature and the solid concentration, with the leaching rate being the highest at 25C and the lowest at 40C, and decreased with increasing solid concentration [101]. The differences in the factors affecting the bioleaching of arsenic in the two studies were due to the different leaching microorganisms used.

In addition to laboratory-scale studies, treatment of tailings using bioleaching technologies has been performed at the industrial scale [102]. Industrial bioleaching processes are divided into irrigation-based principles (dump and heap bioleaching and in situ bioleaching) and vat- and stirred-tank bioleaching [93]. However, some factors limit industrialization.

Whether or not there is biomining or biofouling, the leaching mechanism between microorganisms and minerals is still complex [103]. The training period of microbes at the laboratory scale is long, and it is greatly influenced by other experimental conditions. Therefore, the key to improving the ease of operation of bioleaching technologies in large-scale industrial production is to improve existing bioleaching microorganisms so that they can remain highly active under more complex reaction conditions. In addition, regarding the microbial challenge [104], biological leaching heaps of only a handful of genes in the derivative of acidophilic microorganisms have been published. Although some bacterial genomes from acid mine drainage (AMD) and acidic environments have been used to build replacements, these models cannot fully show the leaching potential; at the same time, it is difficult for researchers to obtain samples of microbes from actual production, making further research difficult.

Cadmium in tailing soil is mainly bound to organic matter and appears in different mineral phases. The bioavailability sequence of lead and cadmium in soil is , with the highest content of cadmium in the soil at around 200400m of tailings [105]. Cadmium inhibits the decomposition of leaf litter by affecting the activity of earthworms and leads to the degradation of soil fertility [106]. Therefore, the treatment of cadmium-containing tailings is very important. A literature review revealed that due to the low efficiency of cadmium bioleaching, there are currently few studies on bioleaching of cadmium pollution in tailings, but those carried out mainly used acid washing, phytoremediation, and other technologies [107, 108]. In the future, it will be necessary to further improve cadmium bioleaching technologies to obtain a higher leaching rate according to the characteristics of cadmium.

Increasing the size of instruments is also a challenge. The small reaction equipment in laboratories enables reactions to be carried out fully, but in large-scale industrial production, the reaction containers are large, and the pH, oxygen concentration, and microbial distribution of the solution cannot be maintained, which leads to a decrease in bioleaching rates.

Compared with traditional physical and chemical techniques, biotechnology is characterized by more creative options for metal extraction and processing [109]. In tailings treatment, the emergence of biological leaching technologies has made up for the shortcomings of physicochemical remediation technologies. However, these technologies still have a high potential for growth.

At present, the indigenous microorganisms used in biological leaching experiments provide excellent genetic data. These data can be used to synthesize microorganisms that meet the requirements of industrial-scale biological leaching of heavy metal tailings through gene recombination to improve the leaching efficiency, reduce industrial costs, and make full use of tailing resources [110]. Future advances in biogenomics will overcome microbial constraints. It will also greatly promote the development of microbial leaching and chlorine-resistant organisms in alkaline environments.

Additional factors influencing biological leaching of heavy metals from tailings have been found recently, which creates new opportunities to improve metal leaching rates. Most of the factors affect the leaching rate by affecting microbial activity. Therefore, future research can build on this breakthrough to enable microorganisms to have genes such as resistance to high pressure and salinity to obtain a greater leaching rate of heavy metals.

Leaching technologies for rare earth elements have also been developed. Owing to the low content of rare earth elements in tailings, biological leaching alone cannot maximize the exploitation of such secondary resources. Innovative technologies such as high-temperature roasting combined with biological leaching, cyanide leaching combined with biological leaching, and bacterial oxidation combined with biological leaching have thus been developed. In addition, through the development of enzymes for biological leaching reactions, heavy metals can be selectively leached from tailings, which can not only improve the metal leaching rate and economic value but also carry out effective treatment for metal pollution [111].

The residue from biological leaching of tailings has also been studied further. One study reported that following recovery treatment of an arsenic/nickel/cobalt leaching residue, the leaching rates of copper, cobalt, nickel, zinc, and arsenic reached 96.31%, 97.23%, 98.56%, 98.46%, and 93.84%, respectively, which is conducive to the effective utilization of resources and reduces the waste of mineral resources [112].

Bioleaching is a sustainable method for metal recovery from tailings and controlling their pollution, which can help save nonrenewable energy consumed in the mining industry and make full use of this secondary resource. In this review, previously published results obtained in the field of bioleaching of tailings were reviewed and presented, including the bioleaching mechanism, the type of influencing factors, and the type of tailings. This review shows that the technologies used for the bioleaching of tailings are mature. In addition to the conventional influencing factors, research on factors such as pressure, microcracks, and salinity has provided new paths for improving the rates of metal leaching. The application of CiteSpace (5.7R2) intuitively visualized that the research hotspots of bioleaching of tailings mainly include biocyanidation, the recovery of manganese, and dissolution kinetics. The discovery of new leaching microorganisms, development of biogenomics, and combination of biocyanidation are new opportunities for the industrial production of heavy metals from bioleaching tailings. The main future development directions identified in this review are the development of the industrial production of heavy metal recovery through biological leaching of mine tailings, while constantly optimizing the process, and to create higher economic and ecological benefits.

Copyright 2021 Xiufang Gao et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

working with lead

working with lead

I am a long way from needing my ballast, but if you are building a submarine or a sailboat, working with the lead is a great way to fill time while you wait for the cash flow to buy the hull materials.

The list of what NOT to do is probably the most important thing to review when working with lead. Both lead dust and the vapors from melted lead are poisonous, especially to children and pregnant women. Lead poisoning in children will cause brain developmental problems and in adults it will destroy the kidneys. There is no treatment, and no way to remove the lead once your body is contaminated. Serious burns are more immediate as lead melts at about 630 degrees F and at that temperature it will easily burn through clothing and skin. Also moisture and hot lead do not mix. Water instantaneously expands to 30 times its liquid volume when vaporized by molten lead and will cause an explosion. So here are some precautions you may want to follow:

I there are3 traditional sources for lead: scrap yards, and tire stores that might sell you their used tire balancing weights, gun ranges. Car batteries do not make the list because processing the acid is beyond the ability of a backyard operation to do safely. The commercial battery recyclers have equipment to reclaim the acid and plastic in batteries so there is more value in the battery that just the lead.

In 2003 we picked up 1700 pounds from a gun range, but not any gun range will do. The one I collect from is in the Hobbs Wildlife Management Area in Arkansas. I happen to stumble onto it while traveling a back road returning from a diving trip, and these are some of the nicest people you'll ever meet. This range actually has an automated system that collects the scrap into a bucket after the bullets hit the steel deflector wall. I only paid 8 cents a pound for the scrap which is 3 cents more that what they were getting from the scrap yard. The problem is that a about half of the weight is trash material consisting of the copper and brass jackets that surround the lead bullets and some bullets are solid copper. Add to that a good share of dirt and rocks that get blown and washed into the trap.

When we started collecting lead for the sailboat in late 2007, we hit every tire store in town. All of the small and lower end stores re-use lead weights but they might have a couple of buckets of damaged weights to sell. It's actually illegal from the stores to reuse the weights because they are more likely to fall off in the road way where they will be ground to dust by the traffic. That will cause some of them to come up with a lie. If your not sure what they are putting on your car, see if your weights have a fresh coat of silver paint and see if they mount the weight on the inside of the rim where it is harder for you to see it. The big national wide outlets like WalMart, Sams, Hibdon Tire, and Firestone will have their own collection programs. The local chain stores and better quality tire stores are your best bet because they will not put used weights on their customers cars. However they will often have contract deals with their wheel weight or battery suppliers that preclude them from selling their used weights. Don't forget the tractor trailer service centers. Semi truck wheel weights are huge compared to car weights. Out of almost 100 stores in the Tulsa area we got one chain of 9 stores and 2 or 3 others that we picked up from once a month. There are a dozen more that we stop at every 2 to 3 months. In less than a year we collected about 10,100 pounds of wheel weights that yielded about 9000 pounds of lead. There is about 20% loss of weight in wheel weights due to the steel clips and trash in the buckets. We also lost about 8 stores from the route in that time because they switched to a contract with their supplier. More and more wheel weights are also no longer made from lead. We pay 2 cents more than the local scrap yards and our price in less than a year has gone from 10 cents to 17 cents a pound in 2008.

The scrap yard will be happy to sell you lead at the going rate.Most yards have "clean lead" which is pipe, sheet and other scrap that should not have any other metals attached. It will often come with dirt and grease and water but 95% of it is lead. They will often also have un-clean lead in the form of wheel weights. You can buy lead wheel weights from the scrap yard for about 25% less than clean lead. After you remove about 20% of that weight that accounts for the steel clips and occasional lug nut you end up with a 5% savings. If you are going to have to melt it down into ingots anyway, then the additional 5% savings may be worth the pain of dealing with the steel clips.

If the Chinese and Indians keep buying cars that need batteries and are just now starting to recycle them. The US is making more bullets for Afghanistan and Iraq than we have since Vietnam. Lead mainly comes from mines that are primarily about producing zinc and so the demand for zinc is a contributor to the availability of lead. Lead smelters bow up, miners go on strike. New battery technologies will not use lead. So there is a mix of things that control the price. Locally that price in 2006 was 32 cents, in 2007 it was 53 cents a pound and in 2008 it is now $1 a pound. Even during the recession of 2008 the price of lead only dropped to 80 cents a pound.

I found a damaged turkey fryer and a couple of 5 gallon propane tanks for $50. This is not a bad way to go if you are processing less than 1000 pounds. If you are going to process thousands of pound then I'd suggest you look a my Wood Fired Smelter on below.

You must have a steel or cast iron melting pot. Since aluminum melts at at 1220F I figured I could melt my lead in the bent pot that came with the fryer. But when I tried a small test batch, the bottom nearly fell out of the pot once the lead started to melt.

(1) A trip to the scrap metal yard turned up steel compressed air tank about 16 inches in diameter. I had the yard torch off about 18 inches of one end and also cut down the collar. A steel plug when in the outlet and it sits collar fits nicely over the burner. After seeing how hot the burner legs got during the first test batch I went back and got some angle iron and gave the pot its own set of legs. Now I can load the pot up with 200+ pounds and not worry.

(2) The tool are a screen on a steel pipe to fish the trash off the top of the molten lead, a steel bucket riveted to a steel handle for scooping out the trash and ladling out the molten lead, and a steel bar to stir and move the trash into the ladle.

(3) If your lead has scrap in it like my gun rage bullets, then you will have a lot more work, but here are some tricks. First off, do not wash the lead thinking you can wash off the dirt, as the lead also disintegrates into a fine dust and it will wash away too. I created a small version of Tar Creek in my back yard and ended up scraping off a half inch of soil in order to remove the lead. Second, do not fill your pot so deep that you can't run an steel bar to the bottom. You will have to routinely push the bullets down into the bottom of the pot as they begin to melt. I didn't do this on my fist full load and after running the burner for 6 hoursI the lead still had not melted. The problem is that heat does not travel well through the air spaces between the pieces of lead and the trash. Starting with a puddle of lead in the bottom from the previous batch also helps. But do not add scrap after there is melted lead in the pot, unless your are sure it is dry. You can start off with wet scrap because it will have time heat up and dry before there is any melted lead.

(4) The best thing I did to speed up the melting process is to put a lid on the pot. My lid is an old metal wash tub.This will trap heat and help start raising the temperature in the lead that is above the molten pool. When using a lid and poking the pile down every 10 minutes or so I can melt 120 pounds of lead in about 2 hours and burn about 2 gallons of propane. If you keep poking the scrap down into the pool of melted lead in the bottom and eventually all of the brass, copper and dirt will be floating on top.

(5) 90% of the scrap can be removed with a ladle and a steel bar. My ladle is actually a 2 quart metal bucket that is riveted onto a piece of flat steel bar. If you build one of these then check the rivets for wear and damage. You do not want to drop a bucket of molten lead! Another steel bar is used to rake the scrap into the bucket. (6) You'll have to dump the trash into a metal bucket, so I got to use my bent turkey fryer pot after all. Do not try using anything but metal, as the trash will still be over 600 degrees. (7) Once you work your way down to the lead you can dip up lead along with the trash floating on the surface and cautiously allow the lead to drain back into the pot.

(8) The last of the trash, which will mainly be dirt can be removed with a wire mesh strainer like the one found in your kitchen. I actually tried a metal kitchen strainer after I welded on a 2 foot handle, but it only lasted through 2 batches. I made a better strainer from a half inch steel pipe with a loop bent into one end and then I wired couple of layers of 1/4 inch hardware cloth wired onto the loop, and finally a couple of layers of aluminum window screen is stitched to the hardware cloth. Be prepared to replace the window screen a couple of times as it will not last more than a few batches if you let it get too hot. I tried adding beeswax which is often used as a flux, for removing impurities like copper and oxides from lead. I did enjoyed the impressive plume of white smoke that preceded the flames that shot up out of the pot but I didn't notice any benefit when it came to the end product. Fluxing sounds important if you are casting figurines or bullets, but it is not important when we are talking about ballast.

(9) My molds are made from 3 inch channel. I have two molds, each with 3, 19 inch lengths of channel welded side by side with ends made from more channel. The steel is over 1/4 inch and they heat up nicely when leaned up against the burner while the lead is melting. You should have two sets of molds, so that one can be cooling while you are pouring the second. (10) It will only take 8 to 10 minutes for the lead to set and then you can dump out the first mold and start over. Each ingot from my molds weights 19 to 20 pounds.

If you want to make life easier on yourself then get lead with little or no trash in it. I picked up a 240 pounds from the scrap yard that was chopped up pieces of lead pipe for 25 cents a pound. I figured this was a pretty good price considering that my bullets from the gun range were half trash material making the actual cost for the extracted lead about 16 cents a pound. After I add in my drive time, trailer rental, fuel and not having to remove hundreds of pounds of trash, the extra 9 cents didn't seem too bad. The trash from the gun range material with the dirt and rocks included has no salvage value, but the scrap yard did take it off my hands without change which is something for the sanitation workers to be grateful about. However I found that my 240 pounds of lead pipe has its own problems.

(11) Lead used to make pipe especially the old lead pipe found in scrap yards as well as the lead that comes from chemical plants and radiation shielding used to line the walls of X-ray rooms contains from 1 to 12% antimony. Antimony is added to make the lead harder and better suited for construction. If your building an fin keel for a sail boat then you'll need between 3 and 5% antimony, but for internal ballast it is not needed. Antimony weighs about the same as iron so it is actually lighter than lead but not by much. It is number 51 on the periodic table and has an atomic weight of 121.76 compared to lead at number 83 with an atomic weight of 207.2. The real problem is that it melts at 630C or 1166F compared to lead that melts at 327C or 621F. My pot would get it to melt, but it would float to the top where it cooled and hardened into the ultimate bath tube ring. It also cools quickly and clogs up the screen strainer as well as hardens around the edges of the ladle. The end result is that my 240 pounds of lead pipe yielded only 180 pounds of ingots. The rest was 20 years of grease and corrosion that came trapped inside the pipes and antimony that was thrown out with the trash. My final cost for extracted lead from the lead pipes was 33 cents a pound, convincing me that the gun range lead at 16 cents a pound was worth the drive to Arkansas and we could always do a little diving in Beaver Lake on the way.

We need 30,000 pounds this time so an upgrade to the smelter was in order. Our source of bullets dried up so we have cultivated a list of tire stores that sell us their used wheel weights. About 20% of what we collect is scrap in the form of the steel clips, and assorted lug nuts, studs, and valve stems.

We picked up 1000+ pounds from 10 stores in 4 hours on one Saturday a month. It will take another four hours to melt them down into ingots. With the steel clips gone we will end up with 800 pounds of lead. And cost to us is about 27 cents a pound. Clean lead at the local scrap yard is 80 cents a pound. We currently have 17000 pounds so we have saved just over $9000 dollars which comes out to about $40 per hour. And we like the Saturday drive together.

(1) The new smelter is a delight to work compared to the old one. It uses the same melting pot, but the pot now has a steel pipe fitted to the bottom. A 90 degree elbow directs the pipe out to the side and then another 90 degree elbow that is not completely tight allows for second pipe stand upright while the batch is melting and then it can be rotated down to pour the lead. A piece of angle iron with a handle is used to direct the molten lead from the pipe into the molds. The melting pot also was fitted with a stand that allows it to be pitched, so that once the scrap left behind has cooled it can easily be dumped into the trash. The melting pot is then surrounded by two 55 gal steel barrels, one stacked on top of the other. The lower drum has an opening for feeding the wood fire below and a hinged hatch in the back that allows it to be pulled away without removing the melting pot, so that the trash in the melting pot can be dumped.

(2) To get the temperature way up; a blower from a old dryer forces air through a 6 inch metal pipe into the fire box and the second barrel acts as a chimney and draw the flames up the sides of the melting pot. The pot can be loaded to the top and in about 60 minutes the blower can be turned off the top barrel removed and more weights can be added. Repeating this process twice allows for over 600 pounds usable lead to be processed in less that 4 hours.

(4) A propane torch is used to heat the pouring pipe when the batch is ready. Then it is just a matter of pulling the pour pipe to the side and directing the lead into the molds with a piece of angle iron. The 1/4" round bar handles welded onto the pour pipe and the angle iron keep the heat and lead away from my hands.

(5) After over 40 uses the pour pipe completely choked off with lead oxide. It was possible to scrap it out but a lot of work, so I just replaced the lower pipe and fittings in order to save time.

(1) Melting down lead ingots is sure a lot more enjoyable the melting down the raw bullets. Just drop the ingots in, skim off a little dross and dip out the molten lead. Do be careful adding cold ingots to hot melt. If the ingots were poured slowly, allowing then to cool in layers, then they will have small gaps between the layers were rain water can collect. A couple of the ingots popped shortly after added then into the hot melt. They should have been heated slowly rather than dropped directly into molten lead.

The lead blocks will need to be lifted out of the compartments in the sled otherwise it would be impossible for me to move it without a small crane. (2) Before the pour we added fillets of plaster into the corners and edges of each compartment in order to round them off , cover the welds, and fill the cracks between the compartments. Be sure to allow a time for the plaster to completely dry.

(3) Before pouring each compartment, short sections of 5/8 inch chain were suspended into the opening so that they will be cast into the lead and become lifting points.Pouring slowly is necessary so that the lead cools and stiffens around the bottom link of chain, otherwise the steel chain will float in the molten lead. Its the strangest thing to see. The aluminum made a great mold and the lead did not stick to the aluminum, but I made a mistake thinking that the lead would contract enough to allow me to easily remove it. Instead it required a 5 foot 2x4 to pry each block out. We connected a chain from the block to one end of the 2x4 and used wood blocking as a fulcrum. And once out of the hole there was no going back in until the block was trimmed down. In hind site I should have added 1/6 inch sheet metal shims to the inside walls of the compartments in order to form a smaller block.

(4) Cutting lead with a skill saw is something I do not recommend, but it works! We first hung tarps from the ceiling in order to prevent the chips of lead from flying all over the shop and back yard, and fly they will. You do not want to be standing in front of the blade! Eye protection, and gloves are a must, I am also wearing a leather sleeve on my left arm. Lead chips and electric motors make a bad combination, so use a cheap saw.Where the blade can not reach across the block you can drag it sideways across the surface and remove a thin layer as you go. Your High School shop teacher would freak if he saw you doing this and rightly so. Be sure you can count to 10 without using your fingers before you try it. (5) After an evening of trimming, trying and trimming a bit more, Carl and I had all of the blocks rough cut to fit into there compartments. Sure glad he was around to lift and move 1200 pounds of lead several times. No need for a trip to the gym tonight.

Flash forward! Its now December 27, 2007. We are in a new house and shop, Carl is missing a kidney due to and IED in Iraq, he and Randi are married, and Kay and I are going to be grand parents in April. Wow! This week the submarine's ballast sled gained about 300 pounds from lead plates that were added to fill the gaps under and around the batteries.

Making the plates was fairly painless but also time consuming. If you are starting here on this page you might consider going back to the top and reading some of the bad things and cautions about working with lead.

(1) I first built a quick mold from some 3/16" aluminum. In the photo to the left the mold has a partition added to form up the smaller plates. The side are 1/2 inch and thinner plates are simply poured shorter. The mold is setting on top of fire brick and clamped down to the work table.

(2) My foundry I use for melting aluminum makes quick work of melting lead. I have also made a modification to the propane supply. If you look close you will see that the regulator is gone and I also drilled out the orifice to something that would be more appropriate for natural gas. These modifications make controlling the flame more difficult, but they also gave me a lot more heat.

(3) When the lead is poured into the mold, it cool and sets very quickly so getting a level surface is impossible. Sorry about the blurry photo. It's not easy to pour 600 degree lead and take a photo at the same time.

(4) Once the lead is in the mold the torch is used to melt the lead again and smooth the surface. This side will never be pretty unless you were to polish it but it will level the bumps out.

(5) If you are impatient you can just wait until the surface has solidified and then pour water on the plate to cool it down. Be careful that the surface really is solid. You do not want to get water under the surface and into the molten lead.

On that point; pouring molten lead onto a wet surface will get a steam explosion that propels molten lead toward your face so be sure to heat the mold to remove any water before the next pour.

(6) The edges can be trimmed with a box knife if you only want to remove a sharp edge. A rough file can be used to remove more material if necessary, but the best tool for cutting lead is a carbide blade.

Just remember that you are creating a serious hazardous waste site when you do this and you will want to get is all done an once and then give your shop a serious cleaning. That includes your cloths. And defiantly no children, expecting, or potential mothers are allowed. You on the other hand may have some brain cells that can be safely exterminated.

cable recycling: optical sorting technology for recycling cables steinert

cable recycling: optical sorting technology for recycling cables steinert

In Germany alone, roughly 150,000 t of cable waste is generated each year. The high-value materials from these electrical cables and their recovery are an important source of valuable raw materials that can be fed back into the economic cycle. With our special sensor sorting techniques, quality equal to that of primary materials can be created that have many possible uses and that can attract the best prices on the raw materials markets. Our UniSort Finealyse colour sorting unit (optimised for the sorting of fine metals with grain size from 3 mm) combines its camera technology with high spectral resolution (over 24 million detections per second) with a compact, dustproof machine design. With the aid of colour detection, the UniSort Finealyse removes, for example, the contaminant of lead from the copper. The removal technology can separate either product or contaminant, to suit your particular requirement, from the material stream using precision compressed air pulses. For this purpose, the 120 high-speed valves can be individually activated.If the material properties or the task change, the sorting parameters can be easily adjusted via a touch panel. This makes our UniSort Finealyse flexible for all further sorting tasks in the recycling of electrical scrap in which colour sorting for grain sizes between 3 and 30 mm can be used. Profit from our STEINERT solutions - but not just in recycling cable granulates and other applications in the fine-grain sorting of non-ferrous metals. Also when generating the correct input material for cable granulation, our technology is ready to provide effective assistance. By cleverly linking different sensors, the STEINERT KSS combination sensor sorting machine creates the optimal cable products for your process. For example, the input of stainless steel into the cable product is effectively suppressed, which acts to conserve the downstream shredding equipment over the long term.

The fraction obtained from multiple shredding and screening stages is then purified of magnetic metals (Fe) using magnetic drums. Next, all non-ferrous metals (aluminium, copper, lead, etc.) are sorted off using the STEINERT EddyC eddy current separator. With its colour sensor the UniSort Flake allows detection of colour differences, in order to remove copper (all red tones), as an example. In the following step the various grey stages, zinc and lead are distinguished and separated.

barconic 3 piece copper plated shaker set - 24 oz bar supplies

barconic 3 piece copper plated shaker set - 24 oz bar supplies

The BarConic 3 Piece Copper Plated Shaker Deluxe Set is the perfect tool for the professional bartender who wants to create mixed drinks with a classic design reminiscent of old copper stills and speakeasies. The shiny, reflective copper plating is elegant and would make for a great showpiece when crafting your favorite cocktail. The 24 oz size is a larger set perfect for volume pouring or just enough space to aerate as you mix. Use the shaker lid with built-in strainer and cap to mix and pour a mixed cocktail to perfection without the risk of spilling. Not Dishwasher Safe

This stylish alternative to the ordinary shaker set adds a classic rustic charm, making them the perfect addition to any home bar or mixologist's tool set. This BarConic 3 Piece Copper Plated Shaker Deluxe Set has everything you need to create to perfect cocktail. We also offer a line of copper plated BarSupplies.com to accompany this set including mugs, bottle openers, jiggers, and bar spoons.

BarSupplies.com Inc is proud to offer a Satisfaction Guarantee!If, for any reason, you are unsatisfied with the products you received, simply submit aSupport Ticketto request a return. Important information and instructions regarding returns are provided via RMA, and therefor are subject to RMA approval. Items sent back without prior RMA approval may be denied. All return requests must be submitted within 30 days of product delivery. Once an RMA is issued, the products must be received back to us, in original condition, within 30 days. Returns will not be accepted unless they are complete. All original boxes, packing materials, parts, components and pieces must be returned to us for a return to be processed. Returns will not be granted without all of the products original packaging and parts. Refunds requested for returns are subject to a 15% restocking fee. Restocking fees do not apply to returns for exchange. ALL associated shipping fees are non-refundable. We do not issue return labels for returns or exchanges.

Custom Orders:As you may be aware, custom printed products cannot be restocked. These types of items may include custom printed glassware and other imprinted bar tools as well as custom made woodshop items such as liquor shelves. In fact, the industry standard for customized products dictates a no return and a no refund policy with the exception of items that are unusable. Unusable items include but are not limited to broken glassware, bent or misshapen bottle openers, cracked or broken license plates, etc. Items with production quality flaws are wholly non-refundable, but may be eligible for a discount or refund. If you receive an order with unusable items, you must contact us within seven days of receiving your order. We require photographic evidence of the unusable items prior to any credits being issued.

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BarSupplies.com Inc. will not be held accountable for the misuse of any products. BarSupplies.com Inc makes every effort to ensure that your package is packed and shipped correctly. However, from time to time, occasional errors are made. If you received damaged, defective or incorrect products, it must be reported within 7 days of delivery. Please note: Photographic evidence will be required for any problems with your order. Problems reported after 7 days of delivery may be disqualified for replacements or refunds. We may request that the incorrect item be returned to us at our expense. If the item is not returned, you may be charged for the incorrect item.

Welcome to BarSupplies.com! Your one stop bar shop that offers the best selection in bartender gear, restaurant supplies, and bar accessories at the cheapest prices online. BarSupplies.com offers wholesale pricing to large restaurant chains and small bars alike.Barsupplies.com LLC boosts incredibly low prices on all bar products. We strive to bring you the latest and greatest products while making your online shopping experience pleasant and easy.

randox zinc assay | reagents | randox laboratories

randox zinc assay | reagents | randox laboratories

Zinc (ZN) is an essential trace element (micronutrient) and plays a vital role in several biological processes 1. ZN is released from food as free ions during digestion. Specific transport proteins facilitate the passage of ZN across cell membranes into circulation. 70% of circulatory ZN is bound to albumin 2. As ZN does not attain redox properties, it is capable of transportation around the biological systems without inducing oxidative damage, which can occur with other essential trace elements like copper 3.

ZN has a key role in growth, reproduction, sexual maturity and the immune system. ZN is vitally important in the functionality of >300 enzymes utilised in the stabilisation of DNA and gene expression 1. ZN can constitute strong, yet readily available flexible and exchangeable, complexes with organic molecules, enabling it to modify the three-dimensional structure of specific proteins, nucleic acids, and cellular membranes, thereby influencing the catalytic properties of many enzyme systems and intracellular signalling. ZN is associated with >50 metalloenzymes with a diverse range of functions and so ZN plays a central role in metabolism, differentiation and cellular growth 3.

Zinc deficiency has been identified as a malnutrition issue worldwide. ZN deficiency is more prevalent in areas of low animal consumption and high cereal consumption. Its not that the diet is low in ZN but more so the bio-availability of ZN which plays a major role in its absorption. Phytic acid has been identified as the main inhibitor of ZN. Adolescents, children, infants, lactating women and pregnant women have increased requirements for ZN and so are at higher risk of zinc depletion. During growth periods, ZN deficiency causes growth failure. The organs most affected by ZN deficiency include: central nervous system, epidermal, gastrointestinal, immune, reproductive and skeletal systems 2.

As there are multiple sources of ZN in the environment, exposure to and toxicity from ZN are not uncommon. Case reports have documented zinc toxicity caused by: overuse of dietary supplements, inhalation from occupational sources, denture cream and ingestion of pennies, to which some of these cases had fatal outcomes 4.

It is believed that ZN toxicity from acute exposure differs significantly from chronic toxicity. In acute exposures, ingestions of ZN sulfate and concentrated ZN chloride will primarily result in gastrointestinal symptoms, such as haematemesis. Renal injury, liver necrosis, coagulopathy and even death have been reported following acute exposures 4.

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