Ball Mill, Jaw Crusher, Mine Hoist manufacturer / supplier in China, offering Mining Parts Forging or Casting Transmission Shaft /Pinion Gear Shaft/Hoist Casting Shaft, Rotary Kiln Spare Parts Rotary Kiln Tyre/Ring, Factory Sell Vertical Shaft Impact Crusher for Sand Stone Making/Limestone Crusher and so on.
CITICTIC Luoyang Heavy Machinery Co., Ltd. The former was CITICHL Heavy Industries Co., Ltd. It was used be subsidiary of CITIC heavy machinery Co., Ltd. The company was founded in 1981 and finished joint stock reform in 2005, which is located in Luoyang city, capital city of nine dynasties in ancient times. With a garden-like industrial park and modern standard plant covering 80000 square meters, CITICTIC possesses advanced equipments, technologies and detecting methods. After more than 30 years ...
India is abundant with stone resources that include granite, marble, sandstone, limestone, slate, and quartzite etc. Stone crushing industry has long history and plays important role in economy development in India.
In stone processing operation, stone products generally are loosened by drilling and blasting and thenconveyedtothe processing operations. Techniques used for extraction vary with the nature and location of thestone deposit. Processing operations may include crushing, screening, size classification, materialhandling and storage operations.
Crushing is the first and integral step in stone processing operation. Stone crushing operation is generally processed in three stages: primary crushing, secondary crushing and tertiary crushing. Each crushing stage involves different types of stone crusher and produces different particle sizes. Stone crusher plant prices are different according to different types and production capacity.
The feeder or screens separate largeboulders from finer rocks that do not require primary crushing, thus reducing the load to theprimary crusher.The stone that is too large to pass through the top deck ofthe scalping screen is processed in the secondary crusher. Cone crushers are commonly used forsecondary crushing. Tertiary crushing is usually performed using cone crushers or other types of impactcrushers.
With the development of mining industry and mining technology, various types of high performance stone crusher plant has been developed. Selection of a crusher for stone crushing production depends on source stone properties such as fragmentation pattern and hardness and the scenario to which the end product will be applied.
SBM is world leading supplier and manufacturer of stone crushing equipment. We have been specialized in crushing technology for long history, and developed all types of stone crusher plant for sale in India. SBM experts can do ore experiments and analyze your requirements, and design cost-effective crushing solution, which requires minimized investment cost and provides optimized profits. If you are interested about stone crusher price in India, or any other information, please contact us.
Two types of stone crusher plants in India have proven capable of producing high quality manufactured sand for concrete and asphalt, VSI crusher and new generation high speed cone crushers. SBM developed leading technology in both crusher types through VSI crusher and HP cone crushers.
Small scale crushing is an integral part in stone crushing industry in India. It makes great contribution to economy development. Stone crushers are primarily small scale industries mostly owned and operated by less educated individuals and are scattered all over the country. For small stone crushing operation, with the restriction of low investment cost, they can afford large new crushing equipment, and prefer small crushing machine, such as small jaw crusher, mini impact crusher and small cone crusher.
Small cone crusher plant cost is relatively cheap, it is usually applied in fine crushing operations for aggregates production, quarrying, mining, minerals processing, construction and recyclingoperations. Theproduction capacity ranges from 10 to 100 TPH. SBM customize large or small crushing solution according to your requirements. Please contact us for more information.
There are large variations in the types of stone crusher setup all over the worlddepending on geographical locations, requirements of final products, closeness to urban areas, raw material properties, availability of plant and machinery locally etc. Primarily the stone crusher industry can be categorizedin three types: small, medium & large.
There are different types of small crushing projects all over the world with a production capacity ranging from 10 to 100TPH. Typically, the crushing plant having only one Jaw crusher or impact crusher used as primary or secondary crusher along with one or maximum two vibratingscreens are grouped as small stone crushers.
As previously mentioned, there are many small stone quarry crushing plants or temporary crushing project for construction, recycling or other applications. They have limited investment cost and cant afford complete new and expensive rock crusher equipment, and prefer used rock crusher for sale in relatively good conditions.
Used jaw crusher is to crush all rock types from the hardest granites to abrasive ones and recycle materials. It has been the world favorite primary used rock crusher for sale in small mining, construction, quarry, and recycling applications.
Used impact crusher is a strong competitive combination of intelligent productivity on tracks tailored for the demanding crushing contractor market. It is ideally suited for crushing medium hard stone like limestone and all mineral-based demolition materials, such as bricks, asphalt and concrete. The used rock crusher for salecapacities ranges from 20tph to 500tph.
The used cone crusher features high capacity and reliability, in addition to top quality and cubical end products as well as low wear part costs. From limestone to taconite, from ballast production to manufactured sand, and from small portable plants, SBM cone crushers provide unbeatable performance in secondary, tertiary, and quaternary applications.
Small scale mines represent a growing and important component of the mineral sector in terms of value output, contribution to the economy and employment.There are many small scale stone crushing activities all over the world; many stone crushing equipment suppliers provide second hand stone crushing machine with low price for sale in Europe, Africa and Asia etc. Theused machinery is with low price and excellent performance, also with long life after sale service. It is the best choice for small or temporary crushing projects. SBM is world leading stone crusher manufacturer; we also customize crushing solution according to customers' requirements. Please contact us, we will analyze your needs and design a best solution for you.
South Africa is the world's second largest vermiculite ore producer, only after the United States. South African vermiculite total reserve is about 73 million tons, accounting for 35.9 percent of the world's reserves. In addition, South Africa is the world's largest exporter of vermiculite. South African vermiculite annual export volume accounts for nearly 90% of world trade. In South Africa, among the domestic production of non-metallic minerals, vermiculite is a major foreign exchange mineral. The major producer of vermiculite is Palabora region, accounting for over 90% of vermiculite total reserve in South Africa.
According to different production requirements, product specifications of vermiculite are as follows:8-12MM ,4-8MM ,2-4MM ,1-2MM ,0.3-1MM ,40-60 mesh,60-80 mesh,80-100 mesh, 100 mesh, 150 mesh, 200 mesh, 325 mesh, etc.
With the development of vermiculites applications, South African abundant vermiculite resource has been extensively developed. And many vermiculite processing plants are built in recent years. In general, we need jaw crusher, impact crusher and vibrating feeder, vibrating screen as well as belt conveyor. After being transported from the mining site, the raw vermiculite mine needs store and select at first, to ensure the vermiculite continuous and stable quality fed into the follow process. In the primary crushing process, we usually choose jaw crusher to crush vermiculite ore into small size within 8 mm. Use vibrating screen to screen the crushed vermiculite into different sizes, and send suitable particles into the next step, while the other part returned for re-crushing. We recommend impact crusher as secondary crusher to crush vermiculite into small size less than 2 mm. At last, send crushed vermiculite to the mill for grinding.Customers can choose different kinds of grinding mill according to different requirements, such as vertical mill, trapezium mill, ball mill, and so on.
And you can choose the mobile vermiculite crusher, which gathers all the machines above together. Compared with traditional and fixed vermiculite processing line, mobile vermiculite crusher has many unmatchable features. It is designed with more reasonable and compact structure, which greatly reduces the occupying area. And compared with fixed crushing plant, mobile vermiculitecrusher can work without disassembly, transportation and installation, soit can greatly reduce the investment. The crusher can move to vermiculite mining area without any environment limit to reduce transportation cost and foundation building cost. It is more flexible and adaptable. And it is easy for installation and maintenance. Our efficient mobile vermiculite crusher adopts advanced manufacturing technique and high-end materials. So it has higher carrying capacity and more reliability. It is easy to adjust the size of the final products. And the crushed materials are in good particle shape. According to different production requirement, it can match with other equipment easily.
According to a series of processing, vermiculite has a wide application. Its main purpose is still to make building materials. In the U.S. consumption structure, vermiculite accounts for 52% used as mortar and cement mixing materials and lightweight concrete aggregate. In English, 40% of vermiculite is used asconcrete, plastering mud, and cement coagulant.It can also be used as adsorbents, fireproof insulation materials, machinery lubricants, soil improvers, and so on.
SBMis professional vermiculite processing equipment manufacturer. We have more than 20 years experience. Our products are welcomed by South African vermiculite miners. All of our products adopt the advanced technology from the world, and made by high quality materials. We can also design a complete vermiculite processing plant according to customers requirement. It is with the features of large capacity, low production cost, long service life and so on.
COPR was used as fill in preparation for building foundations, construction of tank berms, roadway construction, filling of wetlands, sewerline construction, and other construction and development projects.
Chromium is minedas its ore chromitein South Africa, Kazakhstan, India, Russia, and Turkey. Almost 90% of chromium is accounted for in the production of steel alloys (including stainless steel) or in electroplating. Other uses include in tanning where trivalent chromium salts such as chrome alum cross-link collagen fibers, so stabilizing the leather. Chromite has high heat resistance and is used in high temperature refractory applications such as blast furnaces and cement kilns. Chromium compounds are used as catalysts in the production of man-made hydrocarbons such as polyethylene; and, together with copper and arsenic, in wood preservatives. Finally, several chromium salts are strong and durable pigments and are used in dyes and paints, including those that once colored German postboxes and school buses in the US bright yellow. Concerns over contamination of water and soil have led to the replacement of chromium compounds in several applications.
Chromium compounds exhibit several oxidation states, the most common of which are chromium(III) and chromium(VI), trivalent and hexavalent chromium respectively. Chromium(III) compounds are generally stable and water insoluble and are not known to be toxic; similarly chromium metal itself is non-toxic. In contrast, chromium(VI) compounds are oxidants and recognized to be highly toxic.
Chromium metal is obtained commercially by heating chromite ore in the presence of carbon, aluminum, or silicon, and subsequent purification (ATSDR, 2000). Sodium chromate and dichromate are produced by roasting chromite ore with soda ash and are the primary chromium salts from which most other chromium compounds are derived (ATSDR, 2000). Historical uses of chromium by major industry classifications are presented on Table 5.3.1 (ATSDR, 2000).
The first known commercial use for chromium began in the late 1700s as a paint pigment, chrome yellow, derived from crocoite directly or from chromate produced from chromite. As early as 1820 the textile industry was using large amounts of chromium compounds, such as potassium dichromate, as mordants (chemical agents) to fix or stabilize dyes. Mordants bind with the dye and the fibers of a material and prevent bleeding and fading of the colored dye. Other uses of chromium as a colorant were developed. Chromium salts and chromium oxide (Cr2O3) are used to color glass and enamel paint an emerald green. Chromium is used in producing synthetic rubies.
Beginning in the mid-1800s, iron manufactures discovered that adding chromium to steel produced a harder, more useful metal by delaying the transformation that occurs as steel is cooled. Steels with three to five percent chromium were produced beginning in 1865. The high strength and corrosion resistant properties of stainless steel containing more than five percent chromium were discovered in the early 1900s. Chromium steel resists warping and melting under conditions of extreme heat and is ideal for high-temperature applications such as jet-engine components. Chromium compounds are also used to anodize aluminum, a process which coats aluminum with a thick, protective layer of oxide (literally changing the surface into ruby). Stainless and other chrome-containing steels have many applications and the use of chromium in the production of stainless steel and other metal alloys currently accounts for approximately 85% of chromium consumption (ICDA, 2005).
Investigations into chromium plating techniques using chromium chloride and sulfate salts began in the mid-1800s; however, the fundamental principals of chromium electroplating were not discovered until 1924. Most metals plate from chloride or sulfate salts but chromium plates best from chromic acids. This technique was discovered by chance when a chromic acid solution was electrolyzed and a chromium deposit was noted. Chromic acid has the hypothetical structure H2CrO4. However, chromium trioxide, CrO3, the acid anhydride of chromic acid, is sold industrially as chromic acid. Chromium plating, or chrome plating, was first used in the production of jewelry, then for the plating of plumbing fixtures and household appliances, and car manufacturers soon began making chrome bumpers and molding. Chrome-plated articles were esthetically pleasing and functionally desirable due to their shiny surface and resistance to corrosion. Because chrome is a very hard metal and has a low coefficient of friction, chrome plating was also used for extending the life of parts that receive heavy wear, such as automobile cylinders, and was useful in boiler pipes to prevent build-up of scale (mineral deposits).
Refractory materials are highly resistant to heat and are chemically stable. These materials are used as insulation to line the inside of blast furnaces and crucibles used in metal manufacturing. Chromite was initially used as a refractory in France, and bricks of solid chromite cut straight from the mine were used without further refinement or processing up until the 1890s. As a cost-saving measure, manufacturers developed refractory bricks made of crushed chromite and resins that were shaped into bricks. The use of chromium as a refractory material declined in the late 1900s as other refractory materials gained popularity.
Most woods are susceptible to attack by fungus and insects. To make wood more resistant to attack, insecticides and anti-fungal agents can be added. The use of chromium as a wood preservative began in the early 1930s. The most common chromium-containing wood preservative is chromated copper arsenate, or CCA, that is applied to the wood under pressure (also known as the Wolmanizing process). Due to operating procedures that were standard practices at the time, nearly all wood preserving plants 30 years or older present some degree of soil and groundwater contamination (USEPA, 2000). Hexavalent chromium is the most significant soil and groundwater contaminant associated with the use of CCA at these older wood preserving plants (USEPA, 2000). Within the wood itself, Cr(VT) typically is reduced to Cr(III) through a complex series of fixation reactions (Lebow et al., 2003). Potential health concerns associated with direct contact with CCA lumber (primarily due to risks associated with arsenic exposure) led to an agreement between USEPA and CCA producers in the early 2000s to phase out use of CCA-treated wood for most residential applications (USEPA, 2003).
Some additional chromium applications include the use of chromium salts in leather tanning, which was adopted commercially in 1884, and the use of chromium(IV) oxide (CrO2) to manufacture magnetic tape, where its higher coercivity than iron oxide tapes gives better performance. Potassium dichromate is a powerful oxidizing agent and is the preferred compound for cleaning laboratory glassware of any possible organics. Dichromates are also used as oxidizing agents in laboratories for quantitative analysis. As can be seen, chromium is a commercially useful element that is used in a wide variety of industrial, chemical, and refractory applications.
Ferrochromesilicon is another chromium ferroalloy directly produced from chromite ores by carbothermic reduction in submerged arc furnace. The chromium content ranges from 34 to 42%, that of silicon from 38 to 45%, and that of carbon from 0.05 to 0.06%. The mix order is similar to that of smelting high-carbon ferrochromium except that it requires a source for additional silicon. It is produced by smelting together chromite ore and quartz. An alternative to this process is to remelt high-carbon ferrochromium with silica and coke. This is a two-stage process and economically less attractive than the direct smelting process. The low carbon content in ferrochromesilicon is a consequence of a decreased solubility of carbon due to the increase in silicon content. Due to its low carbon and high silicon contents, ferrochromesilicon is used as an intermediary product for the production of the refined grade ferrochromium alloys or in steel-making where any carbon pick-up should be avoided.
Phosphorous is detrimental to both the mechanical properties and corrosion resistance of stainless steels. In the submerged arc smelting of chromite ore, a portion of the phosphorus contained in the charge is vaporized and removed with the off-gas; however, up to 60% can be retained in the alloy, For low phosphorous levels (<0.02%) in ferrochromium, the phosphorus content of the raw materials should be as low as possible. Also a relatively low operating temperature will promote removal of phosphorus into the slag phase, especially under oxidizing conditions. However, due to the highly reducing and hot conditions in the submerged arc furnace, there are no easy ways to produce a low-phosphorus ferrochromium from high phosphorus ore/coke.
Even though several studies have been made on removal of phosphorus from liquid ferrochromium using fluxes such as CaF2CaC2 and CaCaF2, industrial practices mostly rely upon the use of imported low-phosphorus metallurgical coke as a preventive measure.
Chromite is an end member of a complete solid solution series between naturally occurring chromites contain iron and magnesium as substituting impurities with chromium oxide. The other end member is magnesiochromite (MgCr2O4). Chromite ore is usually a combination of spinels with associated minerals such as calcite, magnetite, talc, serpentines and uvarovite. Chromites crystals exhibit an octahedral structure similar to magnetite. The Cr3+ ions are in the octahedral position with oxygen. The chromium rich phase is antiferromagnetic.
The mineral Fe2+[Cr23+]O42 is ferrimagnetic with a very low Curie temperature of 100120K for terrestrial chromites . The transition temperature changes with substitution of the iron and chromium in the chromite. Above the Curie temperature, chromite is paramagnetic.
Chromium from ores of chromite is used to make essential stainless steel, tool steel, armor-piercing projectiles, and is used in other high-temperature applications. It is a strategic metal to the USA, because since 1961, the U.S has been 100 percent dependent upon other nations for chromium. The presence of numerous podiform or smaller lenticular bodies of chromite ore occur in Afghanistan south of Kabul in the Dadukhel area of Logar Province, the Deh Yak district of Ghazni, Jugati in Parwan Province, Sperkay and Shandal in Paktia Province, in the Tanai, Jaji, and Mangal districts of Khost Province, and apparently also new reports are out of its occurrence in the Kunar area.
Discovered originally by geologists from Germany and the US Bureau of mines in the 1950s, exploration of some of the chromite deposits continued by various people up through the 1970s when the Soviet geologists took over (Benham etal., 2009; Anonymous, 2000; Anonymous, n.d.d; Bowley, 2012; Dupee, 2012). Modern assessments have been performed by British, Slovakian, and Afghan geologists. Emplacement of the unusual ores is now understood to have been as original sea-floor, mafic-rich, ophiolite suites that were obducted (thrust) up onto the older Kabul tectonic block and other areas during the Himalayan orogeny.
Most modern mining of chromite for steel hardening in the developed world is from massive ore bodies that are amenable to large open-pit or concentrated underground methods, all of which require massive mining and milling methodologies. In South Asia, however, where such large bodies of chromite do not occur, such as those in southern Africa and elsewhere, for example, the small podiform chromite bodies of South Asia have not attracted much attention from multinational mining companies because of the relatively miniscule sizes in some places size of the individual bodies. Instead, small artisanal, pick-and-shovel mines have been developed in many places in Afghanistan. In fact, not long after American soldiers had been deployed to Afghanistan following the 9/11 events and the invasion of the country by the Coalition forces, a former student of the authors, then employed as an improvised explosive device (IED) specialist, emailed the author about such mining. The author suggested possible armor-piercing IED devices for use against Coalition troops, but subsequent intelligence revealed instead that the chromite was being smuggled across the border into Pakistan where it was sold to Chinese investors and transported by truck up the strategic Karakoram Highway and over the Kunjerab Pass (4693m) to China for use in their steel making instead.
In fact, subsequent elucidation of the kachakbarari (smuggling) networks for this and other commodities has revealed that long-established, criminal mining syndicates control the chromite and other cross-border trafficking (Figure 12.9). Despite the presence of 300 armed security guards tasked with securing the mines in the Khost area alone, estimates are that over 60007000Mt of chromite ore production goes out amounting to over $400,000, with lost revenues to the government each day of more than $20,000. Linkages between the criminal mining syndicates and the Haqqani terrorist networks have also developed.
This artisanal mining of the small, or podiform chromite deposits of Afghanistan has recently come under the scrutiny of a watchdog group in Afghanistan to ensure that both the letter of the mining law is being followed, as well as its spirit (Integrity Watch Afghanistan, 2013). Their work to uncover the current facts is commendable, particularly because their actions are so fraught with danger, inasmuch as many of the existent mining participants do not appreciate any criticism at all and may take offense violently. These problems are compounded by mistakes made by the US DODs Task Force for Business Stability Operation (TFBSO), who also commonly do not much appreciate, or even understand the many cultural/ethnic variations and subtleties in Afghanistan, so that many problems can emerge.
The TFBSO has been assigned the task for the past 34years or so of jumpstarting the Afghanistan mining industry, and in the process in some cases they seem to have fallen in with some people who want to take advantage of weak to no enforcement of mining laws. The result in some cases, as has apparently happened in the Kunar region, has been artisanal mining with little to no governmental supervision or revenue generation. This has been underway in the region for decades with gemstones, and the mining of podiform chromite is now the latest in this sort of activity. For example, the many pods of pegmatites in the profuse granitoid intrusive rocks of Nuristan have long been the main host to diverse gemstones that have been mined without government control for over half a century, so the mineral extraction activity is nothing new; just the fact that it now appears to be chromite that is receiving the attention is new.
The issue at hand with the chromite is that in the Khas Kunar area close to the border with Pakistan the heterogeneous populations of diverse ethnicities have apparently made enough of an accommodation with each other to collaborate in mineral extraction. The Mohmand clan of Pashtuns, however, have laid unofficial claim to most of the chromite deposits in the Khas Kunar region and they have hired local people at 300 Afghanis per day ($5.27) to crush the ore into gravel-sized pieces, which are then put into sacks for transport. It was reported that some 6070tons of the ore per day were smuggled out of the area into Pakistan. Some of the ore was reportedly sold to Chinese traders; other reports were of a Swedish buyer.
Several of the problems associated with this practice of chromite extraction are that the Afghanistan Local Police (ALP) were illegally involved in the process, that the TFBSO had provided training for mineral resource processing and about $13,000 to the police for an ore crusher. A problem in the region, however, is that the ALP are considered by many to be little more than thugs guilty of all sorts of illegal and extra-judicial coercion and nefarious human-rights abuses (Integrity Watch Afghanistan, 2013). The result has been that an important arm of the US DOD and the ISAF forces, the TFBSO, seems to have been co-opted to assist in what they admitted were illegal activities, probably because they thought that the ends were more important than the means. Recognition of these problems in this case has led Integrity Watch Afghanistan (2013) to make a series of recommendations about this chromite mining (Table 12.1), which could be applied far more widely to many other parts of the problematic mining economy of Afghanistan.
The Wolesi Jirga (Lower House of the Afghanistan Parliament) should create an oversight commission to monitor the mining sector on a quarterly basis for revenues, oversee progress on mining projects, establish oversight over state institutions involved with the mining sector, and publish their reports.
Official state mineral law must ensure that mining contracts are not awarded to agents of the government, or to those based upon political connections. Concessions must be awarded only on the basis of, and with a direct reference point to the law.
The International Military Coalition should refrain from interfering in sovereign decisions of the Afghanistan State, yet at the same time continue to build governmental capacity, and provide technical assistance to it in the mining sector.
FeCr is produced by the carbothermic reduction of chromite, FeCr2O4 (formula [(Mg,Fe2+) (Al,Cr,Fe3+)2O4]) (Haggerty, 1991). FeCr is produced in SAFs or direct current (DC) furnaces. In the SAF, the carbonaceous materials are added as coarse reductants and coarse fluxes, whereas in DC furnaces, fine carbonaceous reductants and fluxes are used. The Cr sources can be either coarse ores, oxidative sintered pellets, or prereduced pellets in the SAF and fine chromite ore in the DC furnaces (Beukes etal., 2017). Fluxes such as quartz, magnesite, limestone, and dolomite are used to obtain the required liquid slag properties, such as slag basicity, viscosity, liquidus temperature, and electrical conductivity. The carbon reductants employed are mainly metallurgical coke, coal char, and anthracite, while alternative reductants such as wood charcoal have not yet been used in commercial volumes. Typical specifications of carbonaceous reductants employed in FeCr production are given in Table14.2.
FeCr SAFs are fed from the top, and the structure of the burden is very similar to that of an FeMn SAF. The CO-rich process gas flow through the burden is quite high and therefore, air will not penetrate the burden, irrespective of whether it is an open or closed SAF. The temperature above the charge of an open SAF is usually >600 C because the ignition temperature of the CO gas, which burns at the top of the charge, is >630 C (Niemel etal., 2004). The corresponding temperature in a closed SAF is usually lower and in the range of 200500C. The off-gas from a closed SAF generally contains 75%90% CO, 2%15% H2, 2%10% CO2, and 2%7% N2 (Niemel etal., 2004).
The chromite and carbonaceous reductants will gradually heat up as they descend in an SAF. As in the FeMn process, iron oxide reduction proceeds from the highest to the lowest oxidation state, i.e., hematite (Fe2O3) to magnetite (Fe3O4) to wstite (FeO) to metallic Fe. However, the reduction of chromium-containing oxides is not possible with CO. Cr2O3 is reduced by solid C at temperatures >1250 C, although, in reality, Fe and Cr oxides do not occur in a free form in a chromite spinel, and therefore more extreme conditions might be required to achieve reduction. To minimize energy consumption, the preprocessing of the chromite feed material, such as pelletized oxidative sintering or pelletized prereduction, is common. During the prereduction of chromite, the solid-state reduction of chromite occurs in composite pellets where solid C is heated up to temperatures of around 1300 C before SAF smelting. Although the overall reaction takes place with solid carbon, it is believed that the solid chromitesolid C reduction occurs via the Boudouard reaction. In the prereduction process, metallized Fe and Cr or metal carbides are formed, as shown in Reactions 14.13 and 14.14 (Yamanaka etal., 1973). Complex carbides, containing both metals (i.e., Fe and Cr), might also be formed (Vorob'ev, 2015), but for simplicity these reactions are not shown.
Reactions occurring in composite pellets containing carbon, or in pellets from which Fe oxides have been liberated (e.g., oxidative sintered pellets), within the solid burden of an SAF where the Boudouard reaction (Reaction 14.7) is predominant, are very similar to chromite prereduction reactions. Therefore, the reduction of such pellets can be allowed to continue in this zone inside an SAF to optimize the productivity of the SAF. In the case of ore-fed FeCr SAFs, where very few Fe oxides are liberated from the chromite, carbon reductants with a high CO2 reactivity should be avoided because this will result in the unproductive gasification of solid C due to the Boudouard reaction, as in the Mnalloy process.
As the burden descends further down the SAF, the temperature will continue to rise. Once it is above approximately 1500 C, chromite starts to dissolve in the slag, which leads to a significant increase in the reduction rate (Pistorius, 2002; Urquhart etal., 1974). The reduction reaction then occurs through the reaction of dissolved chromium oxide in the slag with solid C, or with the C and silicon that have dissolved in the metal (Pistorius, 2002; Yamagishi etal., 1974). Hence, one of the most important properties required of the carbon material is its ability to reduce the chromite from the slag to a metallic state. The silicon content of the metal also increases in the high temperature zones. Silicon metal and/or silicon carbide are produced at temperatures in excess of 1800 C (Itaka etal., 2015) but will form at lower temperatures when dissolved in CrFe alloys. The reduced Si in the metal can in turn also serve as a reductant for chromite dissolved in the slag at the slagmetal interface (Pistorius, 2002).
The energy in an FeCr SAF is produced by the electrical currents that come from the electrodes and pass through the coke bed into the metal bath at the bottom of the furnace as in the Mnalloy process. Hence the electrical resistance of the carbon materials is also of importance for this process.
In a DC furnace, the fine feed materials are fed through or in close proximity to the arc, and therefore there is no solid burden but only a liquid bath containing fine carbon particles. DC furnaces are all closed, and the furnace off-gas is therefore rich in CO as in the case of a closed SAF. The gas composition of a FeCr-DC furnace has been reported to be 58%64% CO, 2%6% CO2, 26%34% H2, 0%5% N2, and<1% O2 (Schubert etal., 2011). One of the advantages of the DC furnace operation is the dependence of the process temperature on the electrical resistivity of the process material (Paull and See, 1978; Tuset and Raaness, 1976). Because of this, the slag chemistry and process temperature can be controlled independently of the activity of the slag components participating in the reduction reactions (resulting in the recovery of Cr and low amounts of S and P). Moreover, the viscosity of the slag can be modified for optimal tapping of the furnace and for minimizing refractory wear. When selecting carbon materials, only slag reactivity is of importance, as no solid/gas reactions occur.
Assessing the volume of rare earths and other non-chromate inhibitors that might be required as replacement for chromate is not simple. In the case of chromate chemicals there are primary producers of chromium containing compounds, manufacturers, such as metal finishing and paint companies, supplying product to end-use manufacturers who incorporate chromate into their products, for example aircraft, architectural aluminium, can stock and vehicles as some examples of the major end uses for chromate as an inhibitor. Itemising and summarising chromate consumption on an industry by industry and application by application basis is a complicated task that is easily undermined by lack of data.
A simpler approach has been adopted here to determine consumption figures for chromate chemicals and is aimed at order-of-magnitude assessment of consumption rather than determining the exact figures. In addition to consumption, price is also a consideration. Figure 10.1 compares the trading price range for the mineral chromite, the selected rare earth oxides and other oxides or silicates for late 2012. Prices for rare earths are often expressed as the oxide as are some other elements, hence the oxides are compared in this figure. This snapshot is indicative of relative prices for a range of compounds from which inhibitors could be made. Production of the fine chemical inhibitors will result in increases in the overall costs.
10.1. Snapshot or maximum and minimum trading prices for a range of materials for late 2012. Top: trading prices ranges for specified oxides or silicate (Zircon) in US$/metric tonne. Data for the first quarter of 2013 is also included for Ce and La and show the decrease of prices. Bottom: Expanded price range to include Pr and Nd.
Chromate chemicals used in metal finishing are derived from the mineral chromite. The consumption of chromium is dominated by ferrochrome and stainless steel industries. According to ODriscoll75 in 2011, these industries consumed some 95% of refined chromite production (13Mt) and hence drive the market price for this material. These figures have not changed much over the decade, since, in 2002, total consumption for ferrochrome and stainless steels was 90% of total demand (13.4Mt).76 The price of chromite traded between $US365 and $US450/t (Fig. 10.1).
In 2002, around 1Mt per annum of chromite ore was converted to sodium dichromate (692 000t) of which 224 000t was subsequently converted to chromic acid for the chemical industry. Roughly 50% of this was used for metal finishing in 2002.76 This figure agrees well with 138 834 tonnes consumption for the metal finishing industry determined from the data of ODriscoll for 201175 (in this case by adding the metal plating and pigments figures together). The tonnage range of 112 000t to 139 000t for chromic acid can be used as a basis for assessing how much material is required to replace chromate. Of course, the simple comparison of tonnage ignores the efficiency of inhibition as well as the mix of replacements that are being taken up by industry such as H2ZrF6/H2TiF6 processes for can stock, cobalt-based processes for auto/marine, Zr-based sol-gel for adhesive bonding in aerospace. In the former case the inhibitor efficiency may not need to be directly related to performance as the performance may be a mix of barrier protection and paint adhesion. Thus coating weight of the replacement might be a more pertinent figure to use to estimate consumption. In the latter case (mix of replacements) the total demand for any one of the chromate replacements is likely to be less given that different applications use different technologies. The idea here is simply to get an order of magnitude figure.
Clearly none of the rare earths is mined in the same tonnage as the chromite level. Of the potential replacement inhibitors in Table 10.1, only vanadium and molybdenum are in this range. The amount of vanadium ore mined at 60 000t/year is significant, but falls far short of what would be required to replace chromate given that, like chromium, vanadium supply and demand is overwhelmingly for steel production. Vanadium-based battery technology, which may be critical for energy storage from alternative energy sources, is another emerging technology that will put pressure on vanadium supply and price. Given that the demand for steel is unlikely to decrease significantly, then the amount of vanadium mined would need to increase by around threefold to match the production level similar to chromate supply. Additionally, as vanadium is recovered as a by-product or co-product of processing, the imperative for increasing processing operations is compromised by the need to increase the production of the primary product in the case of vanadium by-product, or have dual demand for the other co-products where vanadium is a co-product of production. Vanadium as a co-product is sourced from phosphate rocks, titaniferous magnetite and uranium ores and as a by-product from bauxite and carbon sources (coal, crude oil, oil shale, tar sands).77 Vanadium pentoxide (V2O5) is the likely starting material for the production of vanadium inhibitors. At around $US30k/t has a distinct price disadvantage over chromite.
While molybdenum has the lowest natural abundance in Table 10.1, the amount of molybdenum mined is large but it is used primarily as an alloying agent for many metals. In the USA in 2010 molybdenum, as ammonium and sodium molybdate for pigments, constituted only 4% of total consumption.78 If this level of consumption is reflected worldwide then total production for pigments would only be 9680t, which is well short of the figure for chromite production. Like vanadium, molybdenum is largely used in alloy manufacture, with roughly 1520% of production used in other applications. Molybdenum is a primary product or co- product from porphyry molybdenum and copper ores as well as a by-product from other copper bearing deposits.78 In this instance, increased demand could more directly drive increased production compared with vanadium, but it would also drive price increases. Bulk ammonium molybdate prices have traded in a range of $US18k to $US30k/t in mid 2013,79 which is 50100 times more expensive than chromite prices.
Zirconium based processes such as fluorozirconoic acid treatments used for can stock are used extensively in industry. As can be seen from Table 10.1, zirconium is considerably more abundant than the rare earths and perhaps the most abundant of possible replacements for chromate. Zirconium comes primarily from zircon or as a co-product with Ti from illmenite and rutile.80 Zirconium inhibitors could be sourced from either zircon or zirconia, but these materials are 10 or 20 times more expensive than chromite, respectively.
Rare earth prices are not so easily established as they are not traded on commodity markets, so accurate records of prices are difficult to establish. However, from sources such as Roskill81 it is possible to establish that dramatic increases in prices, up to 10-fold, have been observed over the decade (20022012). One example includes neodymium oxide which increased from just under $US10/kg in 2001 to nearly $US239/kg in 2011. Recent trends in 2012 and 2013 show that rare earth prices have decreased from their maxima and are beginning to stabilise, albeit at higher levels than prices in 2010.
Other uncertainties which make predicting demand difficult are increased industrialisation in the so-called BRIC countries (Brazil, Russia, India, China) and in the developing world as well as a widening range of applications and more severe environments brought on by climate change. An example of a widening range of applications includes major infrastructure for marginal oil and gas fields with high CO2 and H2S levels, which are very corrosive.82 In response to climate change, infrastructure will be put to new uses, such as transporting CO2 from CO2 emitters such as power plants to sequestration wells. If this CO2 contains a fraction of the pollutants generated and currently discharged in stacks with the CO2, then the CO2/impurity mixture will be very corrosive and thus pipelines carrying the CO2 will need to be protected. Climate change also has the potential to increase the rate of degradation of our infrastructure and thus increase the level of protection required.83 Lastly the social, economic and legal tolerance in the developed world for failure of infrastructure and transport vehicles as a result of poor remedial programmes to treat degradation, has decreased resulting in increased demands for high levels of protection and risk mitigation. All these factors indicate that the demand for coatings and inhibitors are likely to increase for the foreseeable future.
The friability of many chromite ores, e.g. the Bushveld Complex in South Africa, necessitated the implementation of agglomeration processes prior to SAF smelting to ensure a permeable bed. This applies to Process Options B and C. The most commonly applied agglomeration technique is pelletization (both with drum and disk), although briquetting is also used. Pelletization of chromite requires milling prior to agglomeration. Milling and subsequent pelletization also increase the effective surface area for reduction during smelting, which have been linked with improved SEC (Zhao and Hayes, 2010).
Currently dry milling is applied in the pre-reduced pelletized feed process (Process Option C), with a targeted particle size of d90 equal to 75m (90% of the particles smaller than 75m) prior to pelletization (Kleynhans etal., 2012). Previously it was proven that dry milling of chromite ore (and other Cr containing materials) leads to Cr(VI) formation (Beukes and Guest, 2001; Glastonbury etal., 2010). Although not common, some chromite ores, e.g. chromite of the Sukinda belt of Orissa (India) might contain Cr(VI) that occurs naturally (Section 2) (Godgul and Sahu, 1995; Dubey etal., 2001; Tiwary etal., 2005; Dhal etal., 2010). However, as indicated in Fig.7 (Glastonbury etal., 2010), Cr(VI) is formed during dry milling and not merely liberated from the mineral matrix, since no Cr(VI) was formed with dry milling under a nitrogen (N2) atmosphere. The generation of Cr(VI) during dry milling was also acknowledged in the health, safety and environmental guidelines document compiled by the International Chromium Development Organization (ICDA) (ICDA, 2007).
No previously published data (Beukes and Guest, 2001; Glastonbury etal., 2010) can be used to quantify the generation of Cr(VI) by dry milling, since Cr(VI) generation is likely to depend on various factors, e.g. chromite composition, initial ore particle size, targeted particle size, milling equipment design, milling intensity and retention time.
Wet milling does not seem to generate Cr(VI) (Beukes and Guest, 2001). Therefore, ignoring all other aspects (e.g. capital investment, operational costs, integration with other process steps), it can be stated that wet milling has an advantage with regard to Cr(VI) formation. Currently wet milling is used in conjunction with the oxidative sintered pelletized process (Process Option B), with a targeted d80 of 74m.
Presently there seems to be conflicting views with regard to the human health hazards associated with Cr(VI) ingestion. Numerous studies (e.g. Proctor etal., 2002; Guertin, 2004) have indicated that ingested Cr(VI) is not problematic. However, all literature agrees that airborne Cr(VI) is hazardous. Therefore, if dry milling of chromite cannot be prevented, dust prevention, extraction and suppression must be applied. Captured dust must be contacted with water to immediately reduce the risk of human respiratory exposure and such captured dust must be recycled, since it consists of fine feed material. Process water utilized for contacting/capturing milling dust must be treated to reduce Cr(VI), which will be discussed later (Section 4). The wearing of appropriate dust masks must also be made compulsory for operational personnel in the dry-milling section(s).
Cr occurs naturally in the form of crustal rocks but the main source is from various industrial units. It occurs predominantly as ferrochromite (Fe2Cr2O4) and other minerals present in the earth's crust. The main ecological toxic burden is anthropogenic source concerned with industrial operations using Cr, mainly in leather tanning, metallurgical, Cr plating, wood processing, anodizing aluminium, cleaning agents, catalytic manufacture, organic synthesis, textile dyeing and textile pigment production, Cr plating, wood preservation and alloy preparation industries (Alloway, 2013). Out of the total world production of 24,000103 metric tons (gross weight of marketable chromite ore), about 6070% is consumed in stainless steel and alloy preparation. Leather tanning, pigment production, electroplating and other chemical industrial processes use above 15% (Papp and Lipin, 2010). Presently more than 4000 tanneries are involved in chrome tanning processes. In India, tannery industries account for about 20003000 tons/year of elemental Cr discharged into the environment. Around 8090% of leather industry uses Cr as a tanning agent. Effluents from these tanneries is loaded with about 40% of Cr used in the form of Cr(VI) and Cr(III) salts (Sundaramoorthy etal., 2010).
Cr concentration varies from 0.1 to 0.5mg/L in fresh waters and from 0.0016 to 0.05mg/L in sea waters (Kumar and Puri, 2012). As recommended by WHO, the maximum permissible limits for the discharge of Cr(VI) into inland surface and drinking water are 0.1mg/L and 0.05mg/L, respectively. Cr is ranked as the 21st most abundant element present in the earth's crust (Frstner and Wittmann, 2012). It is reported that Cr concentration in the soil ranges from 5 to 3000g of Cr per gram (Polti etal., 2011). Besides natural rocks, major sources of Cr are effluents from various industries, ferrochromium slag, solid wastes containing Cr as by products, leachates and dust particles where Cr concentration is found strikingly above permissible limits.Get in Touch with Mechanic