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P R O C E S S I N G S O LU T I O N S HyperLeach Process Shows Promise for Leach-based Recovery of Base Metals U.K.-based Alexander Mining plc reported in late 2012 that it received notification its MetaLeach Ltd. subsidiary was granted a patent for a "Method of Oxidative Leaching of Sulfide Ores and/or Concentrates" in Australia. The patent describes a method, termed HyperLeach, for leaching one or more target metals from a sulphide ore and/or concentrate, by: • Exposing the ore and/or concentrate to an aqueous solution of chlorine-based oxidizing species in which the hypochlorous acid comprises at least 10 mol% of the chlorine-based oxidizing species; • Allowing and/or facilitating the oxidation of the target metals by the hypochlorous acid, thereby decreasing the pH such that the predominant chlorine-based oxidizing species becomes chlorine; • Allowing and/or facilitating the oxidation of the target metals by the chlorine; • Allowing and/or facilitating the dissolution of the target metals by the solution species formed during the oxidation by hypochlorous acid and/or chlorine; and • Passing the pregnant solution produced thereby to a means for metal recovery. Martin Rosser, CEO of Alexander, said, "The technology described in the patent has the potential application for converting sulphide concentrates, the source of the majority of the world's base metals production and resources, through to metal at the mine site. This would eliminate associated expensive concentrate transport costs and replace smelting and roasting, which would in turn remove the associated environmental problems. It also opens up the possibility of heap leaching some sulphide ores, notably chalcopyrite, the main copper ore." HyperLeach is a hydrometallurgical process developed by MetaLeach for the extraction of metals, especially copper, zinc, nickel, cobalt, molybdenum and rhenium from sulphide ore deposits and concentrates. The process utilizes chlorine-based chemistry to solubilize metals from ores under ambient temperature and pressure conditions. The HyperLeach process can be operated as either heap leach or tank leach. As explained in a company press release, currently nearly all base metal sulphide ores are processed and concen- Red Crescent Resources is studying the use of Alexander Mining's ore leaching technologies for primary recovery of copper and zinc from oxide mineralization at several of its base metals projects in Turkey, an ore sample from one of which is pictured here. Alexander and its subsidiary MetaLeach also are pursuing opportunities for adoption of the leach technologies at sites in the DRC, Australia and South Africa. 86 E&MJ; • FEBRUARY 2013 trated on-site using froth flotation before being shipped off site to a smelter and refinery for further processing. The costs involved in selling an ore concentrate include road transport, shipping, smelter and refinery charges, and can include penalty costs imposed by the smelter, which are deducted from the payable metal in the concentrate supplied. In addition, in many situations mine owners may not be paid for valuable metal byproducts contained in the concentrate. Taken altogether, these charges and costs can amount to up to 40% of value of the metal produced from a mine. According to the company, there is considerable scope to do more on-site processing to value add using hydrometallurgy to generate higher returns for mine owners and to make uneconomic ore bodies economic. Although the HyperLeach process was initially developed to treat low-grade ores to produce high-value metal products on-site at competitive operating costs and relatively low capital costs, the process could also be successfully applied to a wide range of concentrates and mattes. One of the key benefits of the process is that it requires no special purposebuilt equipment, only the addition of an appropriate leaching circuit or leach pads and collection ponds. Unlike previous chlorine-based processes, HyperLeach does not require chlorine gas to operate, as the oxidant can be generated on-site via industry-standard chlor-alkali technology. If a low-cost source of chlorine gas is available, then the oxidant can be generated from this. Another key feature of the process is that it operates at ambient temperatures and pressure. The company claims the process is extremely rapid, with flotation concentrates being leached within minutes. The resultant solution is readily processed using conventional solution techniques, including solvent extraction. The rapidity of reaction and selectivity for sulphides makes HyperLeach suitable for heap leaching of base metal sulphide ores that are too low grade to treat using the conventional grind, float and smelt processes. www.e-mj.com