Selecting the right stainless steel finish for your application is very important. You are probably looking for a long lifespan, corrosion resistance and low maintenance needs. The right finishing is the way to guarantee that stainless steel will behave as expected.
However, the process can be somewhat confusing. There are different standards that offer their own designation for each type of stainless steel surface finish. Some manufacturers even create in-house standards to designate the surface finishes of their products.
To make it simpler for you, we recommend focusing on the most recognised standards around the world. For example, both DIN and ASTM standards are very common. Therefore, we are using these as our examples.
Lets start by comparing the DIN and ASTM finishes in a table format. This gives you a great overview of the possibilities using both standards. Well get into the details of each finish later in the article.
Mill finish is the basic supply condition for stainless steels, no matter whether they are cold or hot rolled. However, most of these steels require further finishing processes to meet the requirements of certain applications.
After the steel is hot rolled in the mill, it is then put through a heat treatment called annealing. Annealing consists of heating the steel and letting it cool down slowly to remove internal stress and reduce hardness. This makes it more ductile and workable.
After the annealing process, the 1D stainless steel is ready for the last step to achieve the designated finish pickling. This process consists of cleaning the surface with acid to remove the scales. Scales form during the previous processes, hot rolling and annealing.
1D stainless steel is sometimes used as the starting point for polished finishes. However, common applications of this stainless steel surface finish involve non-decorative purposes. Thus, the visual appearance is not always relevant. Some examples include:
As this steel is cold rolled rather than hot rolled, the surface finish is more refined. The annealing and pickling processes improve its characteristics in a similar way as with the 1D stainless steel. In this case, pickling is necessary because annealing is performed to remove stress and reduce the hardness resulting from cold rolling.
Similarly to the 1D surface finish, the 2D can be the starting point for polished finishes. It can also be used for some industrial and engineering needs with less critical aesthetics. Common applications for 2D stainless steels are:
Another cold rolled stainless steel where the process is similar to producing 2D. The difference is that there is an extra step in producing 2B stainless steel surface. That step is rolling it one final time with highly polished rolls known as bright rolls.
Due to its dull grey and not very reflective appearance, it is only used in architecture when uniformity of finish is not a requirement. Common applications for the 2B stainless steel finish include, but are not limited to:
Again, there is only a small difference with previously described surface finishes. In this case, we have the bright annealing process added. It consists of annealing the steel under oxygen-free conditions to protect it from oxidation and scaling.
The resulting stainless steel finish is capable of reflecting clear images. It is very smooth and less likely to harbour airborne contaminants and moisture compared to any other mill finishes. This easy-to-clean finish has a typical Ra between 0.050.1 micrometers.
This one is a little different to the rest of the mill finishes. Here, the metal is cold worked after the cold rolling process in order to obtain improved strength. The hardening is done by means of temper rolling on polished rolls. 6 different levels of strength are available depending on the yield strength, tensile strength and elongation.
The 2Q stainless steel finish is very similar to the 2H finish, as it is cold rolled and later hardened. The difference is that the 2Q is hardened and tempered in a protective atmosphere or descaled after heat treatment. Therefore, it is specifically used on martensitic steels which are the ones that respond to these treatments.
A few recommendations apply when selecting a stainless steel for your application. As a starting point, choose a mill finish that is the closest to the desired outcome. This way, the number of additional processes can be minimised.
However, there are standard finishes that are achieved by mechanically polishing and brushing the surface. This means that the surface will be processed by using abrasive materials that effectively cut the surface of the steel to a desirable degree.
The resulting surface finish for mechanically polished and brushed stainless steels will depend on different aspects. Those include the original surface (starting point), type and texture of the polishing belts and brushes, and the nature of the polishing process used.
Due to the process used, the resulting finish provides a rather coarse, unidirectional surface with low reflectivity. The surface roughness can be defined by the manufacturer and agreed with the customer upon request. Most manufacturers define the Ra up to 1 micrometer.
The starting points for these finishes are the same as the previous ones. But now the hot rolled or cold rolled steels are processed with polishing belts or brushes. Thus achieving a more refined surface compared to the 1G-2G surfaces.
However, the result is still unidirectional and not very reflective. The grade of the brush, polishing belt or surface roughness can be specified by the manufacturer. Typical average roughness is between 0.21.0 micrometers, although most manufacturers prefer to stay around 0.40.6 micrometers for the 1J 2J finishes.
The same starting point as the 1K 2K finishes. The last process in this case is polishing and buffing with soft cloth mops and special polishing compounds. This helps to achieve a bright polished finish.
The 1P 2P are non-directional, ultra-smooth and highly reflective finishes with a high degree of image clarity in the reflection. Typical Ra values for these stainless steels are below 0.1 micrometers.
Producing patterned stainless steel finishes includes pressing or rolling with patterned rolls. These operations result in an effectively stiffened sheet. As a result, this allows for thinner gauge cladding, a subsequent possible cost saving and overall weight reduction.
It usually starts with a 2B or 2R mill finish. So, the common processing involves cold rolling, heat treatment, and skin pass on roughened rolls. Sometimes, bright annealing or annealing and pickling can be performed.
The design for the pattern is agreed with the manufacturer and mainly depends on the specific application. However, the main idea of the textures is to use them where surfaces are susceptible to accidental knocks and scratches. Therefore, damages are less likely to be noticed.
The quality mills we offer at Pleasant Hill Grain have a wide range of abilities and use a variety of unique designs. This grain mill overview page addresses common grain milling questions, like: How finely should a mill grind? How important is milling speed? What difference does burr type make? With different mills offering very different degrees of versatility, choosing one can seem overwhelming at firstbut understanding a few grain mill fundamentals will help you narrow your search down to a grain mill thats ideal for your needs.
The single most sought-after function in a grain mill is the ability to make fine flour from whole grains, including gluten-containing grains like hard wheat, spelt or rye, as well as gluten-free (GF) choices like rice, oats and quinoa. For most users, this fine flour ability is a non-negotiable, must have feature. How fine is fine enough? Most home grain mill users are mainly interested in making whole grain bread with excellent rise and texture, and every one of our grain mills will produce an ideal grind for bread flour from a wide variety of grains.
If youre interested in making pastries, youll want a mill that can grind to an ultra-fine texture. The finest grinding ability is also required to make fine flour from white rice, a staple grain for many who follow a gluten-free diet. In a moment well discuss what grain mill characteristics to look for if ultra-fine grinding is among your goals.
Certain design and performance factors are important to understand as you begin the process of selecting a grain mill. The overview below will provide helpful perspective on different mill designs and their suitability to achieve your aims. Our product pages provide the most detailed information on individual mills, but its helpful to understand the forest a bit before you start studying the trees.
The heart of a grain mill is its grinding burrs, and three basic types of burrs are used in home grain mills: Stone burr, impact and steel burr. The type of burrs that a mill uses dictates many of the key characteristics and abilities of the mill.
Quality stone burr mills are made in every size from small to very large, with output speeds to match. Theyre quieter than impact mills. Every stone burr mill we offer has the widest possible texture range; they can produce ultra fine or very fine flour, coarser flour, meal texture, cereal grind, and even cracked grain. The stone burrs in most modern small mills have a synthetic engineered composition for precision, uniformity, efficient grinding, and long burr life. Quality modern mill stones are long lasting, cool-grinding, and never contribute grit to your flour.
Stone burr mills grind all dry grains and beans and some can be used for small quantities of fibrous materials like dried spices. They arent suitable for wet or oily materials. A combination of timeless design and modern technology, these mills are heir to a tradition that spans millennia. Both electric and hand crank stone burr mills are available. Austrian-made KoMo grain mills combine the most advanced ceramic-corundum burr design with German-manufactured motors and handsome hardwood cabinetry. KoMos exciting new Mio line offers the same internal milling design and your choice of colorful trim options, with some components made of revolutionary new Arboblend biopolymer. Mockmill grain mills also offer ceramic-corundum burrs, and feature cabinets made entirely of Arboblend.
Also called micronizers, this popular design offers high speed performance at moderate cost with above-average sound level. Impact mills are electric-only. As seen in the accompanying image, impact mills feature a milling chamber with concentric rings of stainless steel fins. The fins, which never touch each other, spin at tens of thousands of revolutions per minute and burst grain kernels into small pieces as theyre impacted.
Impact mills produce flour only, typically in a range adjustable from coarser flour to very fine flour; they cannot grind a cereal texture, or coarser cracked grain. Theyre suitable for dry grains and beans, and cannot grind oily, wet or fibrous materials. Impact mills have become very popular since their introduction about thirty years ago. The market leaders in this category are the NutriMill Classic and the WonderMill.
While impact mills technically have steel burrs, generally they arent known as steel burr mills, a name that refers to slower-turning mills that crush grain between rotating steel plates or cones (described below.)
Like stone burr mills, steel burr mills turn at relatively slow RPMs, are fairly quiet, and have a wide range of adjustability that starts with cracked grain, runs through cereal and meal texture, and all the way to very fine flour. Few steel burr mills can grind to an ultra fine texture, but the Country Living mill is an exception to that rule as its large precision-cast stainless steel burrs can grind grain (even hard white rice) exceptionally fine.
Most of our steel burr mills are available as hand-crank models, with motor components available to run them on electric power when desired. The popular hand-crank Wonder Junior Deluxe+ grain mill offers an optional adapter for operation with an electric drill. The Wonder Junior mill also crosses burr-composition categories by coming standard with both stone and steel burrs.The Wonder Junior is among the easiest-operating hand crank grain grinders on the market. With the quick change head system you can switch from grinding dry grains, beans and legumes to oily or wet grains, nuts, seeds or coffee, in just minutes.
The Family Grain Mill is a modular system that allows quick-change choices of motor or hand drive units, and processing heads that include a flour mill, grain flaker, meat grinder and food processor. Made in Germany to exacting fit and finish tolerances, the Family Grain Mill offers exceptional versatility.
A hand crank mill will let you make flour without electricity, whether the power goes out unexpectedly or youre at a site that never has power. And to give you the plug-in alternative, motor drives are available for all of our hand crank grain grinders. There are a number of poorly-designed mills on the market that require such a high turning effort that they really arent of any practical use. You dont have to worry about that problem with a mill from Pleasant Hill Grain because we dont sell mills like that. Nevertheless, grinding hard grain into fine flour takes a fair amount of power, and many of our customers like to have a motorizing option for their hand crank mill, both for ease of use and for the higher output speed that a motor provides. Some start out with the whole setup, and others begin with the manual mill and add the motor later.
Flour output speed varies considerably between mills. If youre shopping for an electric mill, consider how important speed really is to you before you give this factor a lot of weight. Once its started, an electric mill will finish its job hands-free while you go about other kitchen tasks. For commercial users, a certain minimum production capacity may be essential. But for a home baker who typically grinds a single batch, you can probably compensate for a somewhat slower output speed simply by starting the mill a couple of minutes earlier. With this in mind, many shoppers find that other characteristics are at least as important as a mills output speed.
The discussion on this page relates mainly to home-use grain mills. If youre a small business owner (bakery, etc.) working with a limited budget, you may be considering using a home-use mill for small scale production grinding. But we also have excellent small commercial grain mills that are designed for continuous-run grinding, and are covered by commercial warranties. Our most popular small commercial grinder is the KoMo XL Plus grain mill, and another commercial grain mill to consider is the Meadows 8 stone burr mill which features natural North Carolina granite burrs. We also offer larger commercial grain mills with burrs up to 30" diameter.Multi-purpose commercial grinder choices include disk mill, plate mill, steel burr mill, hammer mill, pin mill, roller mill and stone burr grain mill options. These mills grind a wide range of wet or dry materials including grain like wheat, corn and soybeans, industrial hemp, plastic, seeds including sesame, flax and teff, coffee, beans including garbanzo beans/chickpeas, crickets for cricket flour/powder, date seeds, roots, taro, cassava, bone, peppers, spices, shells, coconut hulls, wood chips, plastics, waste electronic components, popcorn, and nuts including peanuts for making peanut butter.
Another category of grain mills is flakers. Most often used to make fresh oatmeal from oat groats (oats with the hull removed), flakers create a flake thats thicker and chewier than the paper-thin flakes available in grocery stores. Because flaking grain requires much less energy than grinding flour, most flakers are manual. KoMo makes two of our most popular flakers, the hand-operated KoMo FlicFloc and the electric FlocMan flaker. The modular Family Grain Mill system includes an excellent flaker that can be hand or motor operated. KoMo also builds combination mills that include electric grain mills with electric or hand crank flakers; you can see all of our flakers and grinder/flaker combos here .
The table below lets you compare the features and key specs of many of our most popular grain mills, and more details are available on individual product pages. If you have questions not answered here or would just like to discuss your particular needs, our knowledgeable customer service representatives would love to talk with you.
This iron produces the traditional crisp waffle I almost gave up hope of being able to enjoy again my family and I are able to make and enjoy the delicious, crisp waffle hearts I enjoyed as a child. Invest in this product. The quality is exceptional.
What is ultrafine grinding and what role can ultrafine grinding play in the minerals industry now or in the future? This theme attracted representatives from equipment manufacturers, suppliers of grinding media, mining companies, consultants and academics to a conference in the seaside resort of Falmouth in Cornwall, UK (12-13th June 2006). The conference was attended by 64 delegates from 24 countries spread across all five continents.
While the concept of grinding minerals hardly requires an introduction, it emerged that the definition of ultrafine particles depends on the application: it can relate both to particles in the low m size range and to particles which have been considerably reduced in size. Traditional barriers to ultrafine grinding are the relatively high energy requirement and a perceived reduction in efficiency during further processing. However, technological advances in ultrafine grinding may be welcomed by the mining sector, where the necessity to process increasingly complex ores is presently coupled to buoyant commodity prices.
While conventional milling techniques may produce an ultrafine grind, the required energy rises sharply as the product size, often characterized in terms of the 80 % passing size, d80, decreases. Ultrafine grinding techniques are those techniques which are more energy-efficient than conventional milling techniques in the sub 100 m range. Other advantages over conventional techniques are the option to avoid contamination of the product with ferrous chips, for example from steel balls used as grinding media, lower wear for ultrafine applications, the ability to contain dust and manage heat generation. On the downside, D. Yan states that ultrafine grinding techniques are less predictable than conventional ball mills in terms of energy requirement and grinding performance while throughput may be limited.
During ultrafine grinding, particle breakage occurs by familiar mechanisms: impact or attrition by shear or a combination of these. Classic examples of impact techniques are jetmills where particles are either accelerated against a surface or against other particles moving in the opposite direction. While impact techniques are not suitable for breaking relatively tough materials such as quartz, modified jetmills may be useful for some tough applications. J. Roth (PMT-Jetmill) presented the spiral jetmill as an alternative to classic jetmill designs. The feed is injected into the milling chamber through tangential nozzles while the product is recovered through the classifier rotor located in the middle of the milling chamber. Intense shear between the particles in the milling chamber can produce delamination, preserving or even increasing the aspect ratio of particles. This is beneficial, for example, when talc is ground to enable separation of quartz prior to its application as a reinforcing filler in plastics. In another example, B.G. Kim added that it is attractive to preserve the flaky shape of graphite particles during ultrafine grinding in view of their high conductance.
A. Mc Veigh (Hicom International) discussed application of the Hicom mill for enhancing the recovery of kaolin from china clay waste minerals (silica and mica). Kaolin is commonly used a filler in paper, with platy kaolin enabling the production of lighter and smoother paper. In the Hicom mill, grinding is induced by the inability of the feed to follow the nutating motion of the milling chamber. Product particles escape through openings in the grinding chamber. The Hicom mill can be operated with or without the addition of grinding media. Using relatively fine grinding media, the Hicom mill achieved better delamination than a sand mill currently used by a china clay producer.
Evidence of high-intensity grinding in a Hicom mill was also observed by M. Thornhill, who ground potassium feldspar concentrates with a view to increasing the availability of potassium and assessing their potential as a fertilizer. Trials suggested that ultrafine grinding irreversibly increased the leachability of potassium, although a lower limit to the particle size was observed: very fine particles tended to agglomerate, reducing the specific surface area and the associated leachability of potassium. Comparison with ultrafine grinding of a potassium-rich nepheline syenite concentrate suggest that the effect of mechanical activation achieved by ultrafine grinding is mineral-specific. Although mechanical activation is a difficult concept, E. van der Ven pointed out that ultrafine metal powders can be hazardous on account of their extreme reactivity.
A. Mizitov (Oy Microworld) described the grinding action in a uniRim mill as the equivalent of a pestle-and-mortar. Grinding in the uniRim occurs between the cooled mantle of the grinding vessel and grinding blocks attached to a central rotor. Grinding also occurs well away from the rotor in a planetary mill, which consists of independently-rotating canisters located at the end of arms extending from a central rotor. The combination of centrifugal acceleration of particles towards the rim of the canisters and the even higher angular velocity of the canisters creates a high-intensity grinding environment. E. Kuznetzov (Cyclotec) provided a video to suggest that previous issues such as heat and dust generation, mechanical integrity and discontinuous discharge had been resolved. Scale-up to 100 t/hr is expected to be feasible.
M.K. Abd El-Rahman (CMRDI) studied ultrafine grinding of a variety of minerals in a planetary mill as a function of the rotation speed of the canisters and the presence and size of grinding media in the canister. The advantage of higher rotation speed levelled off at higher speeds, possibly due to cake formation on the canister mantle, while degradation of grinding media increased. Relatively fine grinding media initially led to reduced particle size reduction but, for prolonged grinding, enabled attainment of a smaller product size. This is thought to be due to the smaller interstitial space between media particles, which are generally much larger than the size of product particles. Perhaps surprisingly, a relatively low grinding media-to-feed ratio appeared to increase the initial rate of particle size reduction. For further improvement of grinding performance, the use of chemical additives acting as dispersants was deemed promising.
While stirred media mills stem from a fairly basic design, they have been subject to extensive further development and refinement. For example, the MaxxMill developed by Maschinenfabrik Gustav Eirich consists of a vertical rotating vessel which contains one or more eccentrically-positioned rotors and flow deflectors. Because the MaxxMill operates in dry mode, the smallest particles can be sucked out and classified in an auxilliary cyclone. Particles above a maximum tolerated size are returned to the mill, enabling control of the product size. S. Gerl (Gustav Eirich) presented options to integrate the MaxxMill into processes.
Maelgwyn Minerals Services' M. Battersby introduced the Deswik Turbomicronizer (TM) Mill, a high-speed stirred media mill with a series of impellers along the central shaft. Having evolved from a horizontal design, the vertical Deswik TM Mill is less sensitive to failures of bearing seals and blocking of screens. Feed material is introduced as a slurry at the bottom of the mill, moving upwards in a helix-type flow pattern along a hard-wearing polyurethane resin mill lining. Grinding media are recycled internally to the base of the mill.
Given the technological advances, the focus is turning on the reliability and availability of ultrafine grinding technology in a mining environment. Stirred media mills are starting to feature in large-scale commercial mining applications. Following K. Barns' introduction of the five key process technologies marketed by Xstrata Technology, the application of IsaMill for ultrafine grinding was discussed by D. Curry. Lead/zinc ore at the Mc Arthur River mine in Northern Territories, Australia, requires grinding the ore to below 7 ?m in order to achieve sufficient liberation of galena and sphalerite. Compared to conventional grinding, ultrafine grinding was reported to increase the zinc recovery by 10 %. The IsaMill, which has been developed in partnership with Netzsch Feinmahltechnik, is a high-intensity (up to 300 kW/m3) horizontal disk mill with 8 grinding chambers in series. While media are present to enhance the grinding process, media is retained in the mill without the use of screens. The product is reported to have a narrow particle size distribution, which is considered to be a key factor in maintaining efficient downstream flotation. Using d80 as a parameter, IsaMill may be scaled up, as witnessed by a 3 MW unit being commissioned for AngloPlatinum at Potgietersrust, South Africa.
Anglo Platinum already operates a 2.6 MW unit at Rustenburg, South Africa, for tailings re-treatment, aiming to recover Platinum Group Metals (PGM). C. Rule (Anglo Platinum) explained that ultimate recovery of PGMs locked up in silicates depends on enhanced liberation brought about by ultrafine grinding. A notable improvement in PGM recovery is observed when grinding more tailings below 75 ?m. Anglo Platimum's experience with IsaMill suggests that the wear of mill lining and media consumption were lower than predicted for this application and that the product size distribution and energy consumption were within specification.
The generally advanced nature of stirred media mills was confirmed by the laboratory-scale investigation of two ultrafine grinding techniques by J. Parry. Aiming to liberate fine galena in coarse sphalerite present in ore from Red Dog mine, both the IsaMill and the Stirred Media Detritor (from Metso Minerals) achieved comparable results, as measured with the Mineral Liberation Analyser (from JKTech).
Besides developments in the design and scale-up of stirred media mills, a significant technological breakthrough was achieved with the introduction of a new class of grinding media. Previously, typical grinding media, such as the ore itself, slag, silica sand or river pebbles, suffered from lack of quality, notably inconsistent size and competence. According to P. Hassall (St Gobain-Zirpro), the advent of manufactured media lead to substantial improvement of the media quality through a uniform chemical composition and a high hardness, sphericity, roundness, density, and competency. As a result, the grinding efficiency increases and the energy consumption is lowered. The modern media are typically manufactured ceramic materials such as aluminium oxide, yttrium-, cerium- and magnesium-zirconia oxides and various silicates. B. Clermont (Magotteaux International) described that Keramax MT1 media, containing a mixture of oxides, lowered the energy consumption because there was less sliding friction between hard, spherical media particles. G.A. Graves (Zircoa) emphasised that the smooth surface of media particles, a narrow media size distribution, a high hardness and fracture toughness are vital to achieve energy consumption reduction. Image analysis may be used to monitor the shape and size of media particles. It should be noted that determination of the optimum size of media particles for a given application requires careful consideration. While an application may require media with various media particle sizes, there may be a case for staged milling and ultrafine grinding with optimized media sizes.
While ultrafine grinding can improve recovery and reduce downstream reagent requirements, the effect of extra particle size reduction should be balanced by the cost of additional grinding energy. For example, the Deswik TM Mill reduced a feed with d90 of 89 m to 20 m with 10 kWh/t or 12 m with 16 kWh/t. Ultimately, the economics will decide whether the application of ultrafine grinding will continue to grow.
Our PolarFit ultra-fine grinding mill is a versatile grinding system that provides a cost-effective way to reduce hard to grind materials to smaller particle sizes than can be achieved with conventional impact mills.
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UFG of pyrite concentrates for subsequent leaching is used in ores, where refractoriness to direct cyanidation arises from fine to ultrafine (<20, >0.02m) gold mineral inclusions in the pyrite and/or arsenopyrite. By grinding to 80% passing 10mm a significant fraction of the colloidal size (<0.5m) gold is also being exposed and rendered amenable to cyanidation. On the downside, the huge increase in surface area of pyrite that is created by UFG magnifies 10-fold any preg-borrowing effects, probably assisted by free cyanide, consumption by adsorption onto pyrite surfaces and the formation of thiocyanate (SCN). If there is carbonaceous matter in the UFG concentrate to be leached, it can contribute to significant losses, because of its relatively huge surface and the irreversible sorption of gold (preg-robbing). More details on this technique may be found in Chapter 17.
Ultrafine grinding (UFG) has continued to evolve in terms of equipment development. A number of specialist machines are commercially available including Xstrata's IsaMill, Metso's Vertimill, Outotec's High Intensity Grinding (HIG) mill, and the Metprotech mill. UFG equipment has been developed with installed powers of up to 5MW.
Compared with conventional ball or pebble milling, the specialist machines are significantly more energy efficient and can economically grind to 10m or lower, whereas the economical limit on conventional regrind mills was generally considered to be around 30m. Coupled with improvements in downstream flotation and oxidation processes, the rise of UFG has enabled treatment of more finely grained refractory ores due to a higher degree of liberation in the case of flotation or enhanced oxidation due to the generation of higher surface areas.
In 1993, the Salsigne Gold Mine was reopened. Salsigne treated a gold-bearing pyrite/arsenopyrite ore by flotation, with the flotation tails treated in a CIL circuit and the concentrate reground in a conventional mill to approximately 2530m. The oxygen demand for reground concentrate was high and the rate of oxidation was slow. The concentrate was initially oxidized for approximately 6h using oxygen injection via a Filblast aerator before cyanidation. Additional oxygen was added in in the second CIL stage and hydrogen peroxide was added into the fourth unit to maintain dissolved oxygen concentrations of >10ppm.
Goldcorp have commenced operations at the Elenore Gold Project in Quebec, Canada. The mineralogy of the ore and hence the circuit selection show similarities to those at Salsigne. The main sulfides are arsenopyrite, pyrite, and pyrhottite. The ore is floated, with the flotation tails passing to a tails CIL circuit and the flotation concentrate reground before passing to the concentrate CIL circuit via preaeration tanks designed to achieve 18-h contact with oxygen. The main difference between the Salsigne and Elenore projects is that the Elenore concentrate is ground to 10m and oxidation of the sulfides is substantially complete before cyanidation.
Ultrafine grinding is used to liberate gold finely disseminated in metallic sulfides. KCGM is the first gold mine using ultrafine grinding followed by cyanidation (Ellis and Gao, 2002). The gold sulfide concentrate is grind with an IsaMill to a P80 of 1012m. In the first 3years of operation, high consumption of cyanide and high gold content in leach residues were experienced with difficulty overcoming these issues (Deschnes etal., 2005).
Eleonore Mine is the first commercial application of the IsaMill in Canada (Deschnes and Fulton, 2013). Ultrafine grinding is applied to liberate gold finally disseminated in sulfide minerals. The pyrrhotite concentrate produced by flotation was used to determine the leaching strategy at the laboratory scale. The concentrate grind at a P80 of 10m contained 65% gangue minerals, 23% pyrrhotite, 2.2% pyrite, 9.6% arsenopyrite, 75.5g/t Au, and 5.0g/t Ag. Gold was present as native gold and electrum. A test conducted at 2000ppm NaCN and pH 11.0 produced 97.0% extraction of gold in 72h. It was found that an efficient leaching required only 35ppm DO. However, the presence of reactive pyrrhotite resulted in a cyanide consumption of 31.5kg/t NaCN.
Three key features were identified to optimize the process: the use of a pretreatment, the addition of oxygen and the addition of lead nitrate. A 16-h duration was the optimum retention time for the pretreatment (Figure26.15). In the conditions below, the lowest consumption of cyanide (6.0kg/t NaCN) was associated with a high extraction of gold (97.5% Au; leach residue at 1.92g/t Au). The 8-h pretreatment did not passivate the sulfides as much as the 16-h one and the cyanide consumption increased to 6.6kg/t while the gold extraction slightly decreased to 96.9% (leach residue at 2.36g/t Au). A 24-h pretreatment decreased the gold extraction and increased the cyanide consumption.
Figure26.15. Effect of duration of pretreatment on gold extraction from the Eleonore flotation concentrates. Pretreatment: 0.25L/min/kg oxygen, pH 11.0; cyanidation: 2000ppm NaCN, pH 11.0, DO 35ppm, 20C, 35% pulp density (Deschnes and Fulton, 2013).
For the addition of oxygen in the pretreatment, it was found that increasing the flow rate of oxygen addition from 0.13L/min/kg to 0.25L/min/kg reduced the cyanide consumption from 6.4kg/t to 6.0kg/t (Figure26.16), as well as the gold content of the leach residue from 2.52 to 1.92g/t Au. When the oxygen addition was increased to 0.53L/min, the gold content of the leach residue increased to 2.46, while the cyanide consumption went to 5.5kg/t NaCN (Figure26.16).
Figure26.16. Effect of oxygen flow in the pretreatment on gold extraction from the Eleonore flotation concentrate. Pretreatment: 2.00kg/t lead nitrate, pH11.0, 16h; cyanidation: 2000ppm NaCN, pH 11.0, DO 35ppm, 20C, 35% pulp density (Deschnes and Fulton, 2013).
It was found that increasing the lead nitrate addition from 1.0kg/t to 6.0kg/t in the pretreatment resulted in a decrease in the consumption of cyanide from 7.2kg/t to 1.2kg/t (Figure26.17). At 6kg/t lead nitrate, the pyrrhotite passivation reached a point where the oxygen consumed by the concentrate was significantly reduced. While the DO was usually below 0.5ppm during the entire pretreatment, at 6kg/t lead nitrate, the DO increased beyond 4ppm after 2h. According to the trend, the gold extraction obtained with 23kg/t lead nitrate appears not to be biased and would probably have to be in the range of 2.2g/t Au. At dosages above 4kg/t lead nitrate, the gold content of the leach residue was observed to slightly increase; considering the 0.1g/t variation in fire assay. The gold extraction is not overly sensitive to lead nitrate beyond 2kg/t addition.
Figure26.17. Effect of lead nitrate in the pretreatment on gold extraction from the Eleonore flotation concentrate. Pretreatment: 0.25L/min/kg oxygen, pH 11.0, 16h; cyanidation: 2000ppm NaCN, pH 11.0, DO 35ppm, 20C, 35% pulp density (Deschnes and Fulton, 2013).
With the right conditions, free cyanide concentration in leaching can be significantly reduced, as shown in Figure26.18. A reduction of free cyanide from 2000ppm to 800ppm NaCN had a minor effect on the gold content of the leach residue (which varied by 0.2g/t). For this series, the gold extraction showed an average of 97.0%. A 6.8% decrease in gold extraction occurred when the cyanide concentration was reduced to 550ppm (gold extraction of 92.2%). This is expressed by a sharp increase of the gold content of the leach residue. The cyanide consumption was 1.2kg/t NaCN for the experiment, using a dosage of 800ppm NaCN.
Figure26.18. Effect of cyanide concentration on gold extraction from the Eleonore flotation concentrate. Pretreatment: 0.25L/min/kg oxygen, pH 11.0, 16h, 5.5kg/t lead nitrate; cyanidation: 0.5kg/t lead nitrate, pH 11.0, DO 35ppm, 20C, 35% pulp density (Deschnes and Fulton, 2013).
It is critical to be aware that lead nitrate plays a major role in the composition of the solution that will be processed for cyanide destruction. Figure26.19 shows the variation of solution composition in terms of thiocyanate, iron, copper, and cyanate concentrations as a function of lead nitrate added. The main contributor to cyanide consumption is the formation of thiocyanate, which decreased from 2877 to 843mg/L. The iron concentration also decreased significantly (from 156 to 27mg/L). Because the iron cyanide is a very strong complex, this becomes an issue when its concentration is too high in the barren solution. Difficulties will be encountered in striving to meet the criteria for total cyanide after destruction. The dispersion of thiocyanate concentration indicates some variation in the surface conditions of pyrrhotite prior to cyanidation. In this example, about 50% of the cyanide was unaccounted for. The unaccounted cyanide consumed is probably related to the precipitation of iron cyanide hydroxide species.
Figure26.19. Variation of CNS, Fe, Cu, and CNO concentrations as a function of lead nitrate addition during cyanidation of Eleonore flotation concentrate. Pretreatment: 0.25L/min/kg oxygen, pH 11.0, 16h; cyanidation: 2000ppm NaCN, pH 11.0, DO 35ppm, 20C, 35% pulp density (Deschnes and Fulton, 2013).
Optimization of the plant by the project owner continues after plant commissioning with the aim of maximizing plant throughput within the limitations of ore supply and the maximum capacity of the high capital cost unit processes. This is typically the comminution circuit or downstream concentrate treatment process (e.g.,POX or bio-oxidation plant) for refractory gold ores. Recovery and operating costs are other targets for optimization.
The Macraes Gold Project has treated sulfide ore, oxide ore (in campaigns) and retreated some tailings. The expansion in the throughput of the Macraes Gold Project since plant commissioning in 1990 is illustrated in Figure11.3. The periodic high treatment rates for oxide ore represent periods when the main grinding circuit was used to process oxide ore, during 1991, just prior to plant upgrade in 1999, and twice to process stockpiled oxide ore, in 2001 and 2003. The low rate of continuous treatment of oxide ore through a new mill can be seen post May2003.
In late 1994, the plant was expanded by the addition of flotation and fine grinding capacity. The primary grind size was increased and ultra-fine grinding of flotation concentrate installed to improve gold recovery from flotation concentrate in the subsequent CIL circuit.
In late 1999, a further expansion of the plant was undertaken with the addition of a ball mill (ML350) to reduce the primary grind size and allow a further increase in throughput. In addition, a POX plant was installed to improve refractory gold recovery through oxidation of the flotation concentrate.
In late 2001, a retreatment flotation circuit was installed to recover gold from old sulfide tailings and in mid-2003, a further single-stage SAG mill was installed to allow for the parallel treatment of oxide ore or additional sulfideore.
Each plant expansion was followed by a steady increase in plant throughput. The only element of the plant that became redundant over this period was the ultra-fine regrind facility that was shut down in 1995 due to higher-than-expected operating costs.
The term refractory ore is used to classify different gold ores that are not amenable to the traditional cyanidation processes. Gold in refractory sulfide ores occurs as fine inclusions or in solid solution typically within pyrite, marcasite, and arsenopyrite grains. In this type of ore, because the gold is encapsulated, the interaction with cyanide to form the soluble metal complex is inhibited (Marsden and House, 2006; La Brooy etal., 1994).
Grinding has been used to enhance gold liberation from the host sulfide-containing mineral or for particle-size optimization before oxidative pretreatments; however, when gold is encapsulated in a sulfide matrix, conventional grinding (P80=75m) without a pretreatment usually does not result in improved gold recoveries in the leaching process. Ultra-fine grinding (P8010m) has been proposed as an alternative to unlock gold from sulfidic refractory ores; however, the cost of size reduction to this level makes it applicable only for concentrates (Corrans and Angove, 1991; Gonzalez-Anaya etal., 2011), as is practiced at Kalgoorlie Consolidated Gold Mines, a joint venture between Barrick and Newmont.
Pressure oxidation is one of the main methods used in the industry to improve gold recovery from sulfidic ores. During the autoclaving process, iron sulfides present in the ore are oxidized to ferric sulfate or other oxidized solid compounds such as hematite, thus liberating the gold particles and making them available for leaching. Roasting is also widely used as an oxidative pretreatment for sulfidic refractory ores, in which iron sulfides are oxidized to hematite by oxygen at high temperatures; the porous characteristics of hematite allow for penetration of the cyanide leach solution. Another known method for gold liberation from the sulfide matrix is biological mineral oxidation. In this process, bacteria act as a catalyst for the conversion of iron sulfides in the ore to soluble ferric iron (Fraser etal., 1991). These refractory oxidation processes may be carried out on either a sulfide concentrate or whole-ore feed.
The presence of carbonaceous matter in the ore has also been identified as a cause for the refractory behavior of some gold ores. Like activated carbon, the carbonaceous matter can adsorb the gold cyanide complex, thus reducing the recovery of gold in a cyanide-based process. During the leaching step, once the gold-cyanide complex is formed, it is readily adsorbed by the carbonaceous matter in the ore, thus reporting to the tailings instead of the pregnant solution or activated carbon. The carbon components of the ore responsible for this preg-robbing effect have been identified mainly as native or organic carbon (or noncarbonate carbon), often referred to as total carbonaceous matter (TCM). Encapsulation of gold by carbonaceous ores has also been associated with lower gold recoveries from these types of ores (Dunne etal., 2013) (see also Chapter 49).
The use of adsorbent media such as activated carbon (in carbon-in-leach (CIL)) or resin (in resin-in-leach (RIL)), to compete with the TCM in the ore for gold adsorption from the cyanide leach solution, allows for acceptable gold recoveries from ores with mild preg-robbing characteristics. In the presence of ores with higher TCM content, surface modification or oxidative pretreatments are required (Afenya, 1991).
Traditional methods for pretreatment of carbonaceous ores include flotation, the use of blinding agents, roasting, and chlorination. Flotation has been used to remove carbonaceous material from ores; however, this method is applicable if only most of the gold particles are not associated with the carbonaceous components (Dunne etal., 2013). Blinding is based on selective adsorption of certain chemicals on the carbon surface. Diesel oils, kerosene, paraffin wax, and different surfactants have been used to coat the carbon surface effectively, thus reducing the preg-robbing characteristics of the ore (Zhou etal., 2013). Successful examples of this practice include the Stawell gold mine in Australia (CIL) and the Penjom mine in Malaysia (RIL).
Roasting is the most suitable process to ensure the most complete oxidation of carbonaceous material; high temperature (500600C) and oxygen or air are used to convert carbon to carbon dioxide. Gaseous chlorine (Cl2), hypochlorite (OCl), and ozone (O3) may be used to deactivate the surface of the carbonaceous material in the ore. The mechanism of carbon deactivation is not well understood; it has been suggested that upon exposure to chlorine, the carbon surface is modified, forming carboxyl-type groups that passivate the adsorption sites or change the surface charge, thereby repelling the gold-cyanide ions (see Chapter 49).
Ores in which gold is associated with sulfides and with high carbonaceous matter content are considered double refractory. The northern Nevada region in the United States is a main area where this type of ore is found. Ores in the Carlin Trend District are characterized by the presence of submicroscopic gold (invisible gold) finely disseminated within a sulfide-rich matrix (mainly pyrite, arsenian pyrite, marcasite, and arsenopyrite) within carbonaceous material. Sulfide concentrations vary from 0.5% to 3.5% whereas the carbonaceous matter content can range from 0.5% to 4% total organic carbon (Zhou, 2013). Figure50.1 shows typical gold deportment of two double-refractory ores (a and b) compared with a nonrefractory oxide ore (c). The main gold carrier in the ore shown in Figure50.1(a) is pyrite; the ore has a total sulfide content of 1.43% and a TCM content of 0.94%. In the ore shown in Figure50.1(b), gold is present as native gold, associated with pyrite and arsenopyrite and also as surface gold or gold adsorbed onto the TCM surface. This ore has lower TCM content (0.58%); however, a larger portion of the gold is present as surface gold. This is just a small illustration of the variability of ore components and gold carriers, key factors on selecting the processing method for a given ore.
The elution or stripping properties of a resin is as important as its loading performance. The functional groups on resins have different properties, including the strength of the ionic bond; elution methods therefore have to be developed and optimized for each resin type.
Recognized methods of elution of strong-base resins use zinc cyanide, ammonium thiocyanate, or acidic thiourea. Although each method has advantages and disadvantages (Fleming and Cromberge, 1984), no single method seems to be appropriate for all cases. For example, Fleming (1989) used the zinc-cyanide method for a conventional strong-base resin (A161RIP) used at the Golden Jubilee RIP plant, while for a more selective resin such as Minix, the thiourea method is more effective. Advantages of this stripping procedure are that no regeneration of the resin is necessary and elution is faster, as illustrated in Figure32.2.
The most effective elution technique for Minix makes use of acidic thiourea after an acid wash (1M) to remove nickel, zinc, and some copper. The gold-selective adsorption characteristics of Minix, particularly its high selectivity against cobalt and iron, make it possible to use its advantages (fast kinetics and circuit simplicity) without fear of poisoning the resin (Fleming and Hancock, 1979), as is the case with other commercially available strong-base resins. Elution can be improved by an increase in the thiourea concentration, the acid concentration or the temperature. With an eluant containing 1M thiourea and 0.5MH2SO4 at 60C, elution efficiencies of more than 99.6% can be effected within four or five bed volumes of eluant. Using this elution strategy, the resin is easily stripped to below 100g/t of residual gold.
Electrowinning has proved to be an effective and simple method for recovering gold from the eluate. Electrowinning is done simultaneously with the elution. The barren eluate is recycled to the eluant tank and is recycled for the next elution after the reagents have been made up to their relevant concentrations. Two operating plants, namely Penjom Gold Mine and Barbrook Gold Mine, have now demonstrated the feasibility of this elution strategy for Minix with simultaneous electrowinning.
[Ed.: Caledonia Resources announced5 in January 2006 the commissioning of Barbrook Gold Mine plant expansion, including ultrafine grinding, oxidation, and RIL circuits, and in November 2006 was placed on care and maintenance as a result of damage caused by employees of a labor brokerage company during an illegal industrial action.6 Barbrook was sold7,8 to Vantage Goldfields in 2008.]
Elution of AM-2B resin is similar to that of Minix; but a longer elution time seems to be required (Bolinsky and Shirley, 1996). The process includes a series of elutions, contacting the loaded resin with different solutions. The elution flowsheet differs from plant to plant, and some of the steps described below are optional. Usually the following steps are carried out:
All of the stripping operations are carried out at 5560C and atmospheric pressure. The original design of the stripping section required up to 288h (12days) for elution before achieving gold recovery. In the 1980s, a new stripping technique was developed, which takes from 12 to 24h, a considerable improvement over the original design. Gold from the pregnant thiourea solution is recovered by transferring the solution from the elution section to holding tanks for an electrowinning section. During electrowinning, the solution is circulated between the holding tanks and electrowinning cells. Residual gold on the stripped resin is expected to be below 100g/t.
Combining the elution and electrowinning operations enables elution of AuRIX 100 to be achieved by continuous electroelution using an eluate solution based on 1M sodium hydroxide at 60C (Mackenzie, 1993). In this process, the eluate is passed through a bed of resin and is continually recycled through an electrowinning cell back to the resin bed. In some instances, an improvement to the elution rate can be obtained when the alkaline eluant contains a low concentration of alkali metal cyanide salt and an alkaline salt of a carboxylic acid such as sodium benzoate (Virnig, 1996).
The elution of AuRIX 100 resin was studied exhaustively in a pilot plant in Mexico (Fisher etal., 2000). Initially, resin elution was performed with an eluate composition of 40g/L NaOH, 70g/L sodium benzoate, and 100mg/L free CN. Total eluate volume in the circuit was 64L. Sodium benzoate was found, in bench-scale testing, to accelerate elution kinetics. Elution was carried out at 60C for 6h. At termination of elution, the difference between the gold concentration in the eluant entering and the eluate exiting the column was less than 1mg/L Au. Elution profiles (eluate exiting the column) typical of the sodium benzoate-containing eluate are shown in Figure32.3. Loaded and eluted resin analysis for a sample using this eluate is given in Table32.1.
Elutions were also carried out without sodium benzoate. Figure32.4 shows the effect of sodium benzoate in altering the elution profile. At the end of 6h, the same differential between the eluant entering and eluate exiting the column (less than 1mg/L Au) was obtained. Therefore, sodium benzoate was not a necessary addition for elution of AuRIX 100. Eluate produced by this type of resin is suitable for conventional gold electrowinning with single-pass efficiencies of 66.591.7% and overall gold recovery in electrowinning of 94.599.8%.
A conventional strong-base resin (Duolite A161L) was used at the Golden Jubilee Mine for the recovery of gold, primarily due to the fact that no gold-selective resin was commercially available in the western world at that stage. The zinccyanide elution process is suitable for all nonselective strong-base resins. It is a reversible reaction and therefore, in order for the reaction to proceed to completion, it is important that the concentration of gold in the eluate should be kept as low as possible. This can be done either by the use of a very large volume of eluant, which is pumped in a single pass through the elution column (this is clearly an impractical and expensive approach), or by the use of the electroelution method, in which eluate solution is recirculated continuously between an electrowinning cell and the elution column. The latter approach was adopted at Golden Jubilee (Fleming and Seymore, 1989) and made use of the Mintek-designed electrowinning cell.
In the Golden Jubilee elution, 1 bed-volume of solution containing approximately 0.6M Zn(CN)42 was recirculated from a surge tank through a heating box, elution column, and an electrowinning cell, back to the surge tank. After about 6h of elution at 60C, zinc oxide and sodium cyanide were added to the eluate to compensate for the zinc cyanide that had loaded onto the resin and to restore the concentration in solution to the starting value of 0.6M.
The major disadvantage of the zinccyanide electroelution process is that it is slow; for the first 6months, each elution cycle was continued for a period of 45days. However, since only one elution was necessary per week, the slow elution did not create a bottleneck in the process. Moreover, it was possible to systematically reduce the elution time over 12months of operation, mainly as a result of improvements to the efficiency of the electrowinning process, to attain an ultimate elution period of 48h.
After elution, the resin was washed with water to remove entrained zinc cyanide solution and the resin was then regenerated with 1M sulfuric acid solution. The spent regenerant solution, containing zinc sulfate saturated with hydrogen cyanide gas, was pumped directly into a stirred lime slurry. The zinc cyanide that was produced during this neutralization reaction could be recycled to elution.
Vitrokele is a generic name given to the specialist technology that has been developed for the recovery of cyanide from precious-metal plant process streams (Signet Engineering, 1996) and the recycling of cyanide within the circuit. The resin that has been developed for gold-processing applications, Vitrokele 912, is manufactured by Rohm & Haas in France [Ed.:now part of Dow Chemical Company]. It is understood that the technology was commercially applied at the Connemara plant in Zimbabwe for gold recovery by means of resin-in-solution (RIS) and that significant capital cost savings were realized by use of the resin in place of the conventional activated-carbon process. The flowsheet given for the process suggests that similar chemistry to that used at the Golden Jubilee plant (Fleming, 1989) was employed. Therefore, it is thought that the resin used was probably a strong-base anion exchanger similar to the A161L resin.
Saint-Gobain Zirpro has been instrumental in the development of ceramic media for ultra-fine grinding applications in stirred mills. The history and experience are long, dating back to the mid nineteen seventies. The company was in-fact established in 1971 to refine Zirconium Oxide to meet the Saint-Gobain Glass requirements for high performance refractories. The history of the Glass division is somewhat longer and it celebrated its three hundred and fiftieth anniversary last year.
Zirconia (Zirconium Oxide) and Zircon (Zirconium Silicate) turned out to be significant raw materials necessary to manufacture high quality ceramic beads. Initially beads were produced by a fusion process; the operation required high temperatures and the beads were formed in a molten state. The resulting product (ER120) was based on Zircon and had a density of 4.0g/cc. The beads were round and non-abrasive and were ideal to replace the glass and natural sand products used in the burgeoning stirred or bead mill applications. A comparative increase in density of over 50% was the important factor; greatly enhancing the productivity of the mills. Higher density media, such as steel (7.5g/cc) for example, were largely discounted due to increased abrasion rates and contamination. Therefore ceramic technology was readily adopted by major industries, including pigments, paints and agrochemicals. The products proved to be extremely successful and remained at the forefront of the technology for over twenty years. Increased demands on milling technology were however inevitable and eventually faster, finer, more precise targets were expected. The industry responded with the development of new mill designs which operated at higher speeds, with higher energy and higher throughput rates. A new type of bead was required which would be tough and could withstand the new operating conditions. The result was the evolution of sintered beads, initially based on the same chemistry and having the same density as the fused products. These beads required low temperature forming before densification (sintering) at high temperature. The products proved to be suitable in many of the new applications, providing tougher beads with extended bead lifetimes. Zirpro again developed a class leading product (RIMAX) which gave exemplary performance in many varied fields for example cosmetics, inks and automotive coatings. Today the evolution has continued with the general acceptance of high density (6.0g/cc) stabilized Zirconia beads as the media of choice (Hassall and Nonnet, 2007). The higher density provides the potential for superior and economic grinding and although initially expensive, the controlled wear provides an overall cost effective solution. Zirpro developed a premier product ZIRMIL now widely adopted and widely used in the processing of the most demanding applications, such as pharmaceuticals and ceramics.
Mill design has also evolved to meet the ever increasing demands for ever more specialized materials and applications. At the forefront of these developments are two extremely different projects; the first is nano grinding of electronic materials and the second the ultra-fine grinding of ore bodies in the mining industry. For nano grinding, beads sizes of approximately 100m are required and potentially bead densities increasing beyond of 10g/cc. For mining the environment is severe and beads must withstand high impacts from hard and large feed materials in dilute slurries.
In the nano application Zirpro has launched a derivative of the ZIRMIL range. Advanced ceramic technology and process engineering have enabled the production of 100 and 200m beads in industrial quantities at economic price levels. The material is currently under evaluation in extended customer trials. For mining a composite material MINERAX has been developed and successfully launched into the industry (Fig. 1). It is a tough composite material with a classic density of 3.9g/cc and fully competent in all ultra-fine mining applications.
The Albion technology, schematized in Fig. 14, was developed by Xstrata Plc to treat concentrates produced from refractory base and precious metal ores. The technology is a sulfate based process employing ultrafine grinding (P80 of 1015m) at temperatures of around 8590C, atmospheric pressure to accelerate the kinetics and increase copper recovery level from chalcopyrite, in conventional agitated tanks with corrosion resistant alloy steel shells (Nazari et al., 2012a; Kowalczuk and Chmielewski, 2008; Ellis et al., 2008). The Albion process is an auto-thermal operation, i.e. the leach slurry temperature is set by the amount of heat released in the leaching reaction.
Both the Albion and ActivOx processes make use of ultrafine grinding to achieve sulfide dissolution (enhanced matrix attack) at lower temperature and pressures than required by conventional high pressure oxidation (Ellis et al., 2008). Note that fine grinding produces particles with P100 of <38m while ultrafine grinding produces particles sized within 1 and 20m range (La Brooy et al., 1994). Ultrafine grinding performs the same function as roasting, pressure oxidation, bio- and chemical oxidation which is to break down the sulfide matrix to liberate precious metals locked in silicates or other minerals (Flatman et al., 2010).
According to Hourn et al. (2005), ultrafine grinding of sulfide minerals to particle size of 80% passing 812m will eliminate mineral passivation by sulfur precipitates, as the leached mineral will disintegrate prior to the precipitate layer becoming thick enough to passivate it. The oxygen used for oxidation is injected into the base of the Albion leach reactor at supersonic velocity to achieve the required mass transfer and leaching rate. Chalcopyrite is acid leached through ferrous ion oxidation (Fe3+ being the main oxidizing agent) by oxygen according to the mechanism suggested by Hiroyoshi et al. (2001) in Eqs. (17) and (18). Ferrous oxidation by oxygen takes place as in Eq. (19).
Copper is extracted via SX-EW to produce copper cathodes (Kowalczuk and Chmielewski, 2008). Excess sulfide sulfur in chalcopyrite leaching is present in the residue as elemental sulfur. This makes precious metals recovery difficult as S0 can form a protective coating on the mineral particles. Once present, the coating may hinder the leaching process or even stop it completely. Jeffrey and Anderson (2003) and Lu et al. (2000) have suggested non-cyanide leaching methods such as sodium hydroxide to overcome elemental sulfur issues.
Oraby and Eksteen (2013) have shown that one can leach copper sulfides (including chalcopyrite), oxides and native copper effectively from a copper mineralprecious metal concentrate using an alkaline glycine solution at pH of 1011 with hydrogen peroxide as oxidant. The copper glycinate solution can be treated for copper recovery by a number of conventional technologies such as precipitation using NaSH or solvent extraction. Elemental sulfur formation is prevented by performing the oxidation in alkaline glycine solution.
Hourn et al. (2005) have reported that Albion leach process can operate under either acidic or alkaline conditions (see Fig. 14). In the first case (acid leach), base metals are extracted along with precious metals as by-product, while in the second case; precious metals encapsulated in pyrite, arsenopyrite, selenide or telluride ores are alkaline leached with no requirement of recovering base metals. The alkaline leach process of refractory precious metal bearing sulfides such as pyrite progresses through pyrite dissolution (Eq. (20)) to finally expose the precious metals for subsequent cyanidation.
The Albion process is commercially operational at two plants treating zinc sulfide concentrates that are located in Spain and Germany, while a third Albion process plant operating in the Dominican Republic is treating refractory gold/silver concentrates (Turner and Hourn, 2013).
Uwadiale (1990a) used selective oil agglomeration to upgrade Agbaja oolitic iron ore from a feed value of 45.6% Fe to a concentrate containing 65% Fe at 89.3% Fe recovery. The ore was very fine grained and ultrafine grinding (<5m) was required for liberation. The main iron mineral was goethite with minor hematite and maghemite. Reagent additions were 5mL of oleic acid, 5mL of 10% NaOH and 0.07g of sodium silicate added to the grinding charge of 50g. The pH of the ground pulp was adjusted to 9 and 7mL of kerosene added before agitating the charge in a blender. At the end of the agglomeration process the slurry was screened at 38m to separate the agglomerates from the siliceous gangue. At pH 11, no agglomerates were formed.
Aging Process of holding metals or alloys at room temperature after subjectingthem to shaping or heat treatment, for the purpose of increasing dimensionalstability or to improve their hardness and strength through structural changes, asby precipitation.
Air Hardening Characteristic of a steel that it becomes partially or fullyhardened (martensitic) when cooled in air from above its critical point. Notnecessarily applicable when the object to be hardened has considerablethickness.
Alternating An electrical current which alternately travels in either direction in aCurrent conductor. In 60 cycles per second (60 Hz) AC, the frequency used inthe U.S.A., the current direction reverses 120 times every second.
Annealing Subjected to heat treatment. This usually involves heating, followedby relatively slow cooling of metals or alloys for the purpose of decreasinghardness and increasing the ease of machining or the cold-workingcharacteristics. Annealing may be used to (a) remove effects of strain hardeningresulting from cold work, (b) remove stresses found in castings, forgings,weldments and cold-worked metals, (c) improve machinability and cold-workingcharacteristics, (d) improve mechanical and physical properties by changing theinternal structure, such as by grain refinement, and to increase the uniformityof the structure and correct segregation, banding, and other structuralcharacteristics.
Arc Welding A group of welding processes that produces coalescence ofworkpieces by heating them with an arc. The processes are used with or withoutthe application of pressure and with or without filler metal.
Bevel Angle The angle formed between the cut surface and a theoretical planeperpendicular to the plate surface. Plasma arc cutting tends to remove moremetal from the top than from the bottom, producing a cut angle. (Also referred toas cut angle).
Blowhole A defect in metal caused by hot metal cooling too rapidly whenexcessive gaseous content is present. Specifically, in welding, a gas pocket inthe weld metal resulting from the hot metal solidifying without all of the gaseshaving escaped to the surface.
Bonded Fluxes Bonded fluxes are manufactured by binding an assortment ofpowder together and then baking at a low temperature. The major advantage isthat additional alloying ingredients can be added to the mixture.
Braze A weld produced by heating an assembly to the brazing temperatureusing a filler metal having a liquidus above 450 deg C (840 deg F) and below thesolidus of the base metal. The filler metal is distributed between the closely fittedfaying surfaces of the joint by capillary action.
Carbide Precipitation As a result of prolonged heating or of slow cooling afterpartial or full transformation, atoms of carbon and a metallic element migrate tothe grain boundaries. The atoms here gather and combine as carbides. In highchromium alloys, the affinity (attraction) of chromium and carbon for each otherleads to the formation of a thin inter-granular layer of chromium carbides.
Carbon Steel Steel whose physical properties are chiefly the result of thepercentage of carbon contained in it; and iron-carbon alloy in which the carbon isthe most important constituent, ranging from 0.04%-1.40%. It is also referred toas plain carbon steel or straight carbon steel. Minor elements alsopresent in carbon steel include manganese, phosphorus, sulfur, and usuallysilicon.
Casehardening A heat-treatment process, applied to steel or iron-carbonalloys, by which a harder outside is obtained over a softer interior; depth orincreased hardness depends upon length of treatment.
Coefficient of Friction A value used in engineering calculations which is anindicator of the ability of one material to slide on another. A low coefficient offriction indicates a low rate of wear between sliding surfaces.
Composite Electrode A filler metal electrode used in arc welding, consisting ofmore than one metal component combined mechanically. It may or may notinclude materials which protect the molten metal from the atmosphere, improvethe properties of the weld metal or stabilize the arc.
Constant Current (As applied to welding machines.) A welding power sourcewhich will produce a relatively small change in amperage despite changes involtage caused by a varying arc length Used mostly for welding with coatedelectrodes.
Constant Voltage (As applied to welding machines) A welding power sourcewhich will produce a relatively small change in voltage when the amperage ischanged substantially. Used mostly for welding with solid or flux coredelectrodes.
Covered Electrode A composite filler metal electrode consisting of a core of abare electrode or metal cored electrode to which a covering sufficient to providea slag layer on the weld metal has been applied. The covering may containmaterials providing such functions as shielding from the atmosphere,de-oxidation, and arc stabilization, and can serve as a source of metallicadditions to the weld.
Current (Weld) The amount of electric charge flowing past a specified circuitpoint per unit time Current is the main parameter for welding and has to bechosen to plate thickness and welding speed with respect to the weld quality.The weld current affects penetration and deposition rate. A high current results ina higher and narrower weld with a greater penetration depth. Too high a weldingcurrent can result in undercuts, an uneven weld convexity, burn-through, thermalcracking, an inappropriate merging angle with the body material andundercutting.
Current Density A measure of the degree of arc constriction achieved with aplasma torch. The amperes per square inch of a cross-sectional area of anelectrode. High current density results in high electrode melt-off rate and aconcentrated, deep penetrating arc.
Cut Angle The angle formed between the cut surface and a theoretical planeperpendicular to the plate surface. Plasma arc cutting tends to remove moremetal from the top than from the bottom, producing a cut angle. (Also referred toas bevel angle).
Cutting Gas A gas directed into the torch to surround the electrode, whichbecomes ionized by the arc to form a plasma and issues from the torch nozzle asa plasma jet. (Also referred to as plasma gas or orifice gas).
Defect A discontinuity or discontinuities that by nature or accumulated effected(for example total crack length) render a part or product unable to meet minimumapplicable acceptance standards or specifications. The term designatesrejectability.
Dilution The change in chemical composition of a welding filler metal causedby the admixture of the base metal or previous weld metal in the weld bead. It ismeasured by the percentage of base metal or previous weld metal in the weldbead.
Direct Current An electrical current which flows in only one direction in aconductor. Direction of currentis dependent upon the electrical connections to the battery or other DC powersource. Terminals on all DC devices are usually marked (+) or (-). Reversing theleads will reverse the direction of current flow.
Discontinuity An interruption of the typical structure of a material, such as alack of homogeneity in its mechanical, metallurgical, or physical characteristics. Adiscontinuity is not necessarily a defect.
Distortion All fusion welding methods produce the weld by moving a moltenpool along the weld joint. When the heated metal cools the shrinkage introducesdistortion in (or a change in the shape of) the welded structure.
Divergency The tapered part of the oxygen bore directly behind the throat inhigh pressure (high speed) nozzle designs. The divergency allows the highpressure to become close to atmospheric before it leaves the nozzle. Thisincreases stream velocity and improves cut quality by keeping streamuniform. The increased velocity produces 1015% higher cutting speeds.
Double Arcing A condition in which the welding or cutting arc of a plasma arctorch does not pass through the constricting orifice but transfers to the insidesurface of the nozzle. A secondary arc is simultaneously established between theoutside surface of the nozzle and the workpiece.
Drag The offset distance between the entrance and exit points of the gasstream on the plate being cut, measured on the cut edge. Drag will increase anddecrease with varying conditions such as speed, oxygen pressure, platethickness, oxygen purity, etc.
Electrical Stick-Out In any welding process using a solid or flux cored wire, theelectrical stick-out is the distance from the contact tip to the un-melted electrodeend. Sometimes called the amount of wire in resistance. This distanceinfluences melt-off rate, penetration, and weld bead shape.
Electrode Coating The mixture of chemicals, minerals and metallic alloysapplied to the core wire. The coating controls the welding current, the weldingposition, and provides a shielding atmosphere, deoxidizers to clean the weldmetal, and the welding slag that absorbs impurities from the weld metal. It also helps shape the weld bead and becomes an insulating blanket over theweld bead.
Eutectic Alloy Alloy of a composition that solidifies at a lower temperature thanthe individual elements of the alloy and freezes or solidifies at a constanttemperature to form a fine mixture crystals made up of two or more phases.
Ferrite Number Ferrite Numbers (FN) are the current industry accepted figuresfor specifying ferrite content in austenitic stainless steel weld metal, as approvedby the Welding Research Council (WRC), American Welding Society (AWS) andother organizations. Adopted during the 1970s, ferrite numberis not to be confused with Percent Ferrite that is still used in some cases.
Fillet Weld Size For equal leg fillet welds, the leg lengths of the largestisosceles right triangle that can be inscribed within the fillet weld cross section.For unequal leg fillet welds, the leg lengths of the largest right triangle that can beinscribed within the fillet weld cross section.
Flame Spraying (FLSP) A thermal spraying process in which an oxy/fuel gasflame is the source of heat for melting the surfacing material. Compressed gasmay or may not be used for atomizing and propelling the surfacing material to thesubstrate.
Flashback When gases flashback the flame regresses from outside (off of)the tip in use into the torch body itself. That flame will head to the point where thegases are mixed. The flame will continue to burn at that mixing point as long asfuel and oxygen are present and allowed to flow. Virtually all torches in flashbackmode will whistle, howl, screech, etc. If the operator does NOTHING, the torchwill begin to destroy itself in a matter of seconds, with the flame burning throughthe torch at some weak point. In addition, if unchecked, the flame may continueto migrate upstream seeking fuel/oxygen to continue burning. Ultimately, thatflame front could end up at the gas source itself destroying parts and piecesalong the way. Even if the fuel gas is shut off, with oxygen still flowing, the gutsof the torch can continue to burn.
Flat Welding Position The welding position used to weld from the upper sideof the joint at a point where the weld axis is approximately horizontal, and theweld face lies in an approximately horizontal plane.
Flux In arc welding, fluxes are formulations that, when subjected to the arc, actas a cleaning agent by dissolving oxides, releasing trapped gases and slag andgenerally cleaning the weld metal by floating the impurities to the surface wherethey solidify in the slag covering. The flux also serves to reduce spatter andcontributes to weld bead shape. The flux may be the coating on the electrode,inside the electrode as in flux cored types, or in a granular form as used insubmerged arc welding.
Flux Cored Electrodes A composite tubular filler metal electrode consisting ofa metal sheath and a core of various powdered materials, producing anextensive slag cover on the face of a weld bead. External shielding may berequired.
Full Annealing Heating of steels or iron alloys to above their criticaltemperature range, soaking at the annealing temperature until they aretransformed to a uniform austenitic structure, followed by cooling at apredetermined rate, depending upon the type of alloy and structure required; ingeneral the cooling rate is relatively slow.
Fused Fluxes Fused fluxes are melted ingredients which have been chilled andground to a particular particle size. The advantage of this type flux is the lowmoisture pick-up and improved recycling capabilities.
Gas Ions Shielding gas atoms that, in the presence of an electrical current, loseone or more electrons and therefore, carry a positive electrical charge. Theprovide a more electrically conductive path for the arc between the electrode andthe work piece.
Gas Metal Arc Welding (GMAW) An arc welding process wherein coalescenceis produced by heating with an arc between a continuous filler metal(consumable) electrode and the work. Shielding is obtained entirely from anexternally supplied gas, or gas mixture. Some methods of this process arecalled MIG (Metal Inert Gas) or CO2 welding. MIG welding requires the use of aninert shield gas.
Gas Tungsten Arc Welding (GTAW) An arc welding process whereincoalescence is produced by heating with an arc between a single tungsten (nonconsumable)electrode and the work. Shielding is obtained from a gas or gasmixture. Pressure may or may not be used and filler metal may or may notbe used. (This process is frequently called TIG welding.)
Globular Transfer Mode of metal transfer across the arc where a molten balllarger than the electrode diameter forms at the tip of the electrode. Ondetachment, it takes on an irregular shape and tumbles towards the weld puddlesometimes shorting between the electrode and work at irregular intervals. Occurswhen using shielding gases other than those consisting of at least 80% argonand at medium current settings
Heat Affected Zone The area of the base metal that did not become molten inthe welding process, but did undergo a microstructure change as a result of theheat induced into that area. If the HAZ in hardenable steels is cooled rapidly, thearea becomes excessively brittle.
Heat Shield A device which is located on the very front of a mechanized torch.Its purpose is to provide electrical isolation from the nozzle during piercing andcutting operations. In addition, it providesthe path in which the shield gas impinges the arc at the exit orifice of the heatshield.
High Frequency (as applied to gas-tungsten arc welding) An alternatingcurrent consisting of over 50,000 cycles per second at high voltage, lowamperage that is superimposed on the welding circuit in GTAW power sources. Itionizes a path for non-touch arc starting and stabilizes the arc when weldingwith alternating current.
High Speed Steel Special alloy steel used for high-speed cutting and turningtools, as lathe bits; so named because any tools made of it are able to removemetal much faster than tools of ordinary steel.
Inductance (as applies to short circuiting arc welding) A feature in weldingpower sources designed for short circuiting arc welding to retard the rate ofcurrent rise each time the electrode touches theweld puddle.
Inert Gas A gas, such as helium or argon, which does not chemically combinewith other elements. Such a gas serves as an effective shield of the welding arcand protects the molten weld metal against contamination from the atmosphereuntil it freezes.
Insulator A material which has a tight electron bond, that is, relatively fewelectrons which will move when voltage (electrical pressure) is applied. Wood,glass, ceramics and most plastics are good insulators.
Inverter Power Source A high performance plasma power source designwhich takes advantage of advanced power semiconductor circuitry to reduce thesize and weight of the transformer and hence the overall size of the powersource.
Low Hydrogen Electrodes Stick electrodes that have coating ingredients thatare very low in hydrogen content. The low hydrogen level is achieved primarily bykeeping the moisture content of the coating to a bare minimum.
Martensite A structure resulting from transformation of austenite at temperatureconsiderably below the usual range, achieved by rapid cooling. It is made up ofultra-hard, needlelike crystals that are a supersaturated solid solution of carbonin iron.
Mechanized Welding Pertaining to the control of a process with equipment thatrequires manual adjustment of the equipment controls in response to visualobservation of the operation, with the torch, gun, wire guide assembly, orelectrode holder held by a mechanical device.
Metal Inert Gas (MIG) Welding An arc welding process wherein coalescenceis produced by heating with an arc between a continuous filler metal(consumable) electrode and the work. Shielding is obtained entirely from anexternally supplied gas, or gas mixture. MIG welding requires the use of aninert shield gas.
MMA (Manual Metal Arc) Welding An arc-welding process whereincoalescence is produced by heating with an arc between a covered metal (stick)electrode and the work. Shielding is obtained from decomposition of theelectrode covering. Pressure is not used and filler metal is obtained from theelectrode.
Off-Center Refers to the coating being eccentric and thicker on one side of theelectrode than the opposite side. Also referred to as Fingernailing, which isntalways due to coating eccentricity. Could be a result of formulation as well.
Orifice Gas A gas directed into the torch to surround the electrode, whichbecomes ionized by the arc to form a plasma and issues from the torch nozzle asa plasma jet. (Also referred to as plasma gas or cutting gas).
Peening The mechanical working of metal by means of hammer blows torelieve stresses and reduce distortion. Peening is recommended for thickersections (over 1 or 2) of some alloys on each successivepass. Experience has shown that peening helps to reduce cracking. Peeningmay decrease the ductility and impact properties; however, the next pass willnullify this condition. For this reason, the last surface layers should not bepeened.
Penetration (1) The depth below the surface of the base metal to whichwelding heat is sufficient forthe metal to melt and become liquid or semi-liquid. Also called the depth offusion. (2) The ability ofarc or electrode to reach into the root of the groove between two members beingwelded.
Plasma Arc Cutting (PAC) An arc cutting process that uses a constricted arcand removes the molten metal in a high velocity jet of ionized gas issuing fromthe constricting orifice. Plasma arc cutting is a direct current electrode negative(DCEN) process.
Plasma Gas A gas directed into the torch to surround the electrode, whichbecomes ionized by the arc to form a plasma and issues from the torch nozzle asthe plasma jet. (Also referred to as orifice gas or cutting gas).
Plasma Arc Gouging Gouging utilizing a plasma arc for metal removal. Anelectric arc contained inside a gas shield is passed through a constricting orificein order to generate extremely high temperatures and a high velocity stream ofionized gas. This stream Rapidly melts the metal on which it is focused and thenblows the molten material away.
Post Weld Heat Treatment Reheating the weldment to 1100F to 1350F afterwelding and holding at that temperature for a specified length of time. Heattreating allows additional hydrogen to escape, lowers the residual stresses due towelding, and restores toughness in the heat affected zone.
Preheat Temperature The temperature to which many of the low alloy steelsmust be heated before welding. Preheating retards the cooling rate, allowingmore time for the hydrogen to escape, which minimizes under-bead cracking.Preheat temperatures can vary from 10F to 500F on sections to300F to 600F on heavy sections, depending upon the alloy.
Pulsed MIG Welding Process is used mainly for welding aluminum andstainless steel. The method of controlling the transfer of the droplets by currentpulses from the power source makes it possible to extend the spray range down.The process provides a stable and spatter free arc.
Pulsed Power Welding An arc welding process variation in which the power Iscyclically programmed to pulse so that effective but short duration values ofpower can be utilized. Such short duration values are significantly different fromthe average value of power. Equivalent terms are pulsed voltage orpulsed current welding.
Pulse Transfer Mode of metal transfer somewhat between spray and shortcircuiting. The specific power source has built into it two output levels: a steadybackground level, and a high output (peak) level. The later permits the transfer ofmetal across the arc. This peak output is controllable between high and lowvalues up to several hundred cycles per second. The result of such a peak outputproduces a spray arc below the typical transition current.
Radial crack A crack originating in the fusion zone and extending into the basemetal, usually at right angles to the line of fusion. This type of crack is due to thehigh stresses involved in the cooling of a rigid structure.
Residual Stresses Internal stresses that exist in a metal at room temperatureas the result of (1) previous non-uniform heating and expansion, or (2) acomposite structure composed of a ductile constituentand a brittle one.
Root Crack A weld crack originating in the root bead, which is usually smallerand of higher carbon content than subsequent beads. Crack is caused byshrinkage of the hot weld metal as it cools, placing the root bead under tension.
Secondary Gas Unlike the plasma gas, the secondary gas (also referred to asshielding gas) does not pass through the orifice of the nozzle. It passes aroundthe nozzle and forms a shield around the arc.
Semi-Automatic Welding Welding with a continuous solid wire or flux Coredelectrode where thewire feed speed, shielding gas flow rate, and voltage are preset on theequipment, and the operator guides the hand held welding gun along the joint tobe welded.
Shielded Metal Arc Welding (SMAW) An arc-welding process wherein coalescence is produced by heating with an arc between a covered metalelectrode and the work. Shielding is obtained from decomposition of theelectrode covering. Pressure is not used and filler metal is obtained from theelectrode.
Shield / Shielding Gas Unlike the plasma gas, the secondary gas (alsoreferred to as secondary gas) does not pass through the orifice of the nozzle. Itpasses around the nozzle and forms a shield around the arc.
Short Circuiting Transfer Mode of metal transfer in gas metal arc welding at low voltage and amperage. Transfer takes place each time the electrode touches or short-circuits to the weld puddle, extinguishing the arc. The short-circuitingcurrent causes the electrode to neck down, melt off, and then repeats the cycle.
Slag The brittle mass that forms over the weld bead on welds made with coatedelectrodes, flux cored electrodes, submerged arc welding and other slagproducing welding processes. Welds made with the gas metal arc and the gas tungsten arc welding processes are slag free. Less oxidation generally makesslag more difficult to remove. Reducing speed usually helps.
Slag Follow Refers to how the slag follows the puddle. If the slag is close, itcrowds the puddle, making it more difficult for the welder to observe the arc. Ifthe slag follows fast, it allows for faster travel speeds. Good slag follow is whenthe puddle is clear with the travel speed at a rate that keeps thepuddle oblong.
Slope or Slope Control A necessary feature in welding power sources usedfor short circuiting arc welding. Slope Control reduces the short circuiting currenteach time the electrode touches the weld puddle.
Spark Test A test used to identify a metal. The metal is brought into contactwith a power driven, high speed grinding wheel which produce spark patterns.These patterns are unique to several classes of ferrous metals.
Spray Arc Transfer Mode of metal transfer across the arc where the moltenmetal droplets are smaller than the electrode diameter and are axially directed tothe weld puddle. Requires high voltage and amperage settings and a shieldinggas of at least 80% argon.
Stabilized Stainless Steel A high-chromium steel that does not lose itschromium from solid solution by precipitation, because of the addition ofelements that have a greater attraction for carbon than does chromium.
Stress Relieved The reheating of a weldment to a temperature below thetransformation temperature and holding it for a specified period of time. Afrequently used temperature and time is 1150F. for 1 hr. per inch of thickness.This reheating removes most of the residual stresses put in the weldment bythe heating and cooling during welding.
Stringer Bead A straight weld bead opposed to a weaving bead. In surfacing,the weaving bead produces less dilution because the weld puddle is always in contact with the part of the bead produced on the previous oscillation rather thanthe base metal.
Submerged Arc Welding An arc welding process that uses an arc or arcsbetween a bare metal electrode or electrodes and the weld pool. The arc andmolten metal are shielded by a blanket of granular flux on the workpieces. Theprocess is used without pressure and with filler metal from the electrodeand sometimes from a supplemental source (welding rod, flux, or metalgranules).
Swirl Baffle It serves is a mounting platform for the nozzle, sets up a swirlingdirection of the gas through the small holes in the swirl baffle and carries theelectrical current to the work piece.
Temper (1) The amount of carbon present in the steel: 10 temper is 1.00%carbon. (2) The degree of hardness that an alloy has after heat treatment or coldworking, via the aluminum alloys. This usually lowers the hardness and strength and increases the toughness of the steel.
TIG (Tungsten Inert Gas) Welding An arc welding process whereincoalescence is produced by heating with an arc between a single tungsten (nonconsumable)electrode and the work Shielding isobtained from a gas or gas mixture. Pressure may or may not be used and fillermetal may or may not be used. (Also called Gas Tungsten Arc Welding GTAW)
Toe Crack A crack originating at the junction between the face of the weld andthe base metal It may be any one of three types: (1) radial or stress crack; (2)under-bead crack extending through the hardened zone below the fusion line; or(3) the result of poor fusion between the deposited filler metaland the base metal.
Travel Angle The angle less than 90 degrees between the electrode axis and aline perpendicular to the weld axis, in a plane determined by the electrode axis and the weld axis. This angle can also be used to partially define the position ofguns, torches, rods, and beams.
Trimix or Triple Mix A shielding gas consisting of approximately 90% helium,7-1/2% argon, and 2-1/2% carbon dioxide used primarily for short-circuiting arcwelding of stainless steels. Maintains corrosion resistance of the stainless steeland produces good wetting and excellent weld bead shape.
Under-bead Crack / Cracking A weld defect that starts in the heat affectedzone and is caused by excessive molecular hydrogen trapped in that region. It issometimes referred to as cold cracking, since it occurs after the weld metal hascooled.
Weathering Steel Low alloy steel that is specially formulated to form a thintightly adhering layer of rust. This initial layer prevents further rusting and thus,the need to paint the steel is eliminated. The main alloys in this steel are copperand chromium.
Weld / Welding A localized coalescence of metals or nonmetals producedeither by heating the materials to the welding temperature, with or without theapplication of pressure, or by the application of pressure alone and with orwithout the use of filler material.
Work Angle The angle less than 90deg. between a line that is perpendicular tothe cylindrical pipe surface at the point of intersection of the weld axis and theextension of the electrode axis, and a plane determined by the electrode axis anda line tangent to the pipe at the same point. In a T-joint, the lineis perpendicular to the non-butting member. This angle can also be used topartially define the position of guns, torches, rods and beams.
China manufacturing industries are full of strong and consistent exporters. We are here to bring together China factories that supply manufacturing systems and machinery that are used by processing industries including but not limited to: grinding machine, grinder, milling machine. Here we are going to show you some of the process equipments for sale that featured by our reliable suppliers and manufacturers, such as Ultra Fine Powder Grinder. We will do everything we can just to keep every buyer updated with this highly competitive industry & factory and its latest trends. Whether you are for group or individual sourcing, we will provide you with the latest technology and the comprehensive data of Chinese suppliers like Ultra Fine Powder Grinder factory list to enhance your sourcing performance in the business line of manufacturing & processing machinery.
Applicationcalcium carbonate, barite, dolomite, calcite, limestone, kaolin, bentonite, marble, gypsum, quartz, feldspar, clay, talc, fluorite, white mud, mica, refractory material, glass, total about 1000 kinds of materials.
Ultra fine powder millMicronizer powder mill is suitable for the super fine grinding of all kinds of crisp materials whose Mohs hardness is below 7, such as calcium carbonate, barite, dolomite, calcite, limestone, kaolin, bentonite, marble, gypsum, quartz, feldspar, clay, talc, fluorite, white mud, mica, refractory material, glass, total about 1000 kinds of materials.
Micronizer powder mill is a device that breaks solid materials into powder by grinding, Such comminution is an important unit operation in many processes. It is usually used in Metallurgy, building materials, chemical and mine industries.
Micronizer powder mill is mainly formed by mill body, blower fan, ultra-fine analyzer, finished product cyclone container, bag de-duster and air pipe. The elevator, storage bin, electric control cabinet, powder feeder and crusher are optional for the demands of customers.
When the grinding mill is at work, the main bearing and each dial are driven by electromotor through reducer, and all the grinding rollers are rolling in the ring channels driving by dial through plunger. The materials are driven to the edge of the turn plate by the centrifugal force and fall down into the grinding chambers. The high-pressure air blower constantly inhales air, airflow with crushed materials are brought to classifier whose high-speed impeller will screen the airflow:
The unqualified particle size will fall and return to the mill for being reground while the qualified particle size mixed with air will go into the cyclone powder collector. Most of the qualified powders will fall and exit from the discharging valve at the bottom; A small proportion of the fine powders, with airflow, moves to the dust cleaner. The materials from the above two lots are sent by the conveyor to get finished powders packed. In addition, filtered clean air will be emitted from muffler in the end.
With yearsaccumulation of experience in R&D, the HCH ultra-fine grinding mill is new ultra fine pulverizing equipment designed by HongCheng. This mill is widely used to grind any non-metallic minerals with Mohs hardness below 7 and moisture below 6%, such astalc,calcite, calciumcarbonate, dolomite,bentonite,kaolin, graphite, carbon black etc.. Product fineness can be adjusted within a range from 325 mesh to 2500mesh and its disposable fineness can reach D97 5um. HCH ultra-fine grinding mill is especially suitable for ultra fine grinding. After a long period of market application practice and user authentication, the device HC1395 model was certified by the China Association of calcium carbonate for energy-saving equipment in China's calcium carbonate ultra-fine processing industry. HCH1395 is the biggest ultra fine circle-roll grinding mill in China.
Technological process: The pre-grinding raw ore material will be crushed into particles10mm and transport to the feeding hopper by the elevator, then feed into the grinding chamber by the feeder. The grinding rollers equip on the rotary table rotates around the centre shaft. There is flexible gap between the roller and ring. The rollers rotate outward by the centrifugal function to compress the fixed ring. The rollers also self- rotates around the roller pin. When material passed through the gap between the ring and roller, the material will be smashed by the rotating rollers. Four layers of rollers. Material will be grinded 1st time when passing the 1st layer of roller and ring. Then be grinded second, third and fourth time when loop through each layer rollers. Thus the materials were grinded sufficient and obtain much fine powder. The powder fallen down onto the bottom table by gravity will goes up to the classifier for separation by the airflow from blower. The qualified fineness passing from the classifier will be collected by the pulse bag collector as final product, while unqualified fallen down for regrinding till passing through. The powder goes with air flow into the pulse bag filter and collects by the discharging valve.The wind path is in circulation and the airflow is in negative pressure. There will be no dust escape, so the equipment can ensure a no dust operation in workshop.
HCH Ultra-fineGrinding Mill is widely used to grind any non-metallic minerals with Mohs hardness below 7 and moisture below 6%, such as talc, calcite, calcium carbonate, dolomite, bentonite, kaolin, graphite, carbon black etc.. This kind of mill is especially suitable for ultra finegrinding. The fineness can be adjusted from 0.045mm(325 mesh) to 0.005mm(2500 mesh), whose range is much wider than that of traditional RaymondMill.
Higher production capacity and lower power consumption:Non metallic mineral particles feed which feedingsize is less than 10mm, canbeone-time processedas < 10 m powder (97% passing). The particlesize less than 3um accounted for about 40%,which contributes to a largerspecific surface area.It has the advantages of low cost,high efficiency, andgoodproduct fineness.
Wide fineness and flexible adjustment: Turbine classifier (patent no.: ZL201030143470.6). The fineness can be adjusted flexibly from 0.04mm (400 mesh) to 0.005mm (2500 mesh). Products with various fineness can meet the market needs and improve your competitiveness.
Environmental protection: The pulse collecting system will remove 99.9% of the dust, ensuring dust-free operation environment. The pulse dust collection system is Hongcheng special invent comply for the environment protection requirements.
Thorough CleaningThe pulse dust collection system is adopted with pulse-jet type of cleaning. By utilize the compression air to shoot clean each filtering bag. High and complete dust cleaning. Prevent bags from powder stocking.
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The ultra-fine grinder machine is suitable for the industries of medicine, agriculture, food, chemical industry, alloy, metallurgy, geology, scientific research.,etc. With excellent Eversun technology, it can grind various types of Chinese medicine, precious medicinal materials, ores, chemical raw materials into ultra-fine powder, such as donkey-hide gelatin, frankincense, astragalus, notoginseng, hippocampus, dodder, Ganoderma lucidum, licorice, pearl, and other materials with different properties.This grinder is also suitable for food superfine grinding, spice superfine grinding, and condiment superfine grinder.
This machine adopts a high-speed single-phase motor, with precise structure, high efficiency, no dust, clean and hygienic, simple operation, power-saving and safety. Its also qualified for GMP standards.
The raw material enters the crushing chamber through the feed valve and is impacted by the impact hammer, causing the strong collision, friction, and shearing to achieve ultrafine crushing. The pulverized material enters the classification chamber with the rising of the airflow. The material that meets the particle size requirements enters the collection system through the impeller classification, and the particles that do not meet the particle size requirements return to the pulverization chamber to continue pulverization. The entire production process is fully enclosed and continuous operation, without dust pollution.
Please contact our Eversun professional engineers, and inform the material name, target fineness and output, we will recommend the appropriate model of ultra-fine powder grinder machine to you according to your needs.Get in Touch with Mechanic