Engineering and Mining Journal - Whether the market is copper, gold, nickel, iron ore, lead/zinc, PGM, diamonds or other commodities, E&MJ takes the lead in projecting trends, following development and reporting on the most efficient operating pr
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GRAVITY SEPARATION cific gravities, such as are found in allu- vial mineral sands. In modern flow- sheets, the gravity table provides the final concentrating stages of high-vol- ume rougher treatment by gravity spirals. The company's Wilfley product line is marketed to the recycling industry for the separation of metals in electrical and electronic scrap, Bailey told E&MJ.; "These units have long been in use in Europe for copper-cable reprocessing, and remain highly respected and capa- ble in newer, advanced plants for pro- cessing electrical and electronic waste. "In some cases these units operate with feed sizes well outside recom- mended gravity-table use," he said, "for example minus-6 mm, but they still provide the necessary separation in a way that is unmatched by more accepted dry-processing routes." Holman-Wilfley continues to find new niche applica- tions for its line of gravity tables. Shaking Tables Still Play a Role Shaking-table technology may appear archaic to many mineral processing engineers, yet as Chris Bailey, manag- ing director of UK-based Holman- Wilfley Ltd., told E&MJ;, the company is still finding new applications for its two well-known brands. "We have remained committed to the development of gravi- ty tables, providing niche separating areas in the mineral processor's flow- sheet—often still unmatched by alter- native more recent technology develop- ments," he said. "This is coupled with an expansive demand in minerals from developing-world markets such as China and India for specific products like tin metal and titanium pigments. "Tables are often needed at the end of a circuit so, for example, we see our units being used for cleaning-up pre- concentrates from Knelson concentra- tors in gold-recovery plants." Bailey went on to explain that Holman technology evolved strongly in the 1960s and 1970s in tin-processing flowsheets around the world, and that these machines are now well-proven for relia- bility and for the metallurgical advantage of 'spreading' the concentrate products over a wider discharge area—allowing finer control of product grades. This design also lends itself to the separation of difficult minerals that have close spe- 58 E&MJ; • NOVEMBER 2012 Expanding Application Interest As can be seen, interest in gravity-sep- aration technology is by no means at a low ebb. Take, for example, the use of cones in heavy-mineral recovery, or spi- rals in coal and iron-ore processing. The Australian company, Mineral Tech- nologies, reported that during 2010- 2011 it supplied ArcelorMittal with the largest single spirals order in its histo- ry, used for iron-ore upgrading at the Mont Wright operation in Canada. The company has also supplied its Kelsey centrifugal jigs to customers in Australia, South Africa, Brazil, Peru, Bolivia, India and the U.S.A. for pro- cessing zircon, rutile, tin, tantalum, tungsten, gold and nickel. Meanwhile, in 2011 German manu- facturer allmineral won a contract to supply an 80-mt/h alljig® unit for Rio Tinto's low-grade iron-ore pilot plant in Western Australia, a unit that can han- dle both fines and lump material up to 32 mm as well as treating a wide range of particle-size ratios, the company says. It had earlier supplied two alljigs to Outokumpu's Tornio ferrochrome plant in Finland, where they are used for reprocessing smelter slag. And MBE-CMT reports that over 300 of its Batac jigs are now in operation around the world, handling iron, tin and manganese ores and alloy slags, as well as coal. The main advantages of Batac jigs, the company said, are higher effi- ciency, better product quality, higher availability and greater throughput rates, with units offering throughput rates of between 30 and 1,000 mt/h while handling 1–150-mm feed sizes. Gravity separation is clearly still a valuable component in the mineral-pro- cessing toolkit and, as new applications are identified within the non-coal sec- tor, its niche position looks certain to expand further. allmineral has supplied its alljig technology to a number of major producers worldwide for handling iron ore, industrial minerals and—pictured here—recovering metal from slag. www.e-mj.com