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Leaching Laterites: Two New Processes Make Progress By Russell A. Carter, Managing Editor 86 E&MJ; • JULY 2014 www.e-mj.com P R O C E S S I N G S O LU T I O N S Nickel ore has traditionally been mined by underground methods from deeply buried sulphide deposits that are amenable to conventional concentration methods. These deposits are steadily being depleted and new world-class sul- phide nickel resources are hard to find. Laterite deposits, on the other hand, are relatively plentiful and generally mas- sive—with some containing almost a bil- lion tons of mineralized material—in addition to being located near the sur- face and mineable by economical open- pit techniques. But they're also low grade, with limonite-type laterite de- posits containing around 1%-2% Ni and saprolite-type ore a little more, up to 2.5% Ni—and they have other specific characteristics that make acceptable rates of metal recovery a difficult propo- sition. Nevertheless, they are estimated to contain more than 70% of the world's known nickel resources and are a tanta- lizing target for metal producers, both large and small, industry entrepreneurs and mineral processing experts. Presenters at technical conferences over the past few years have highlighted laterite ore processing challenges, which include high energy requirements involv- ing both heat and pressure, high con- sumption of expensive reagents and sul- phuric acid, and environmental risks, to name just a few. Over the past century, a number of hydrometallurgical processes have been developed to recover nickel from laterite ores, each with its own set of advantages and flaws and all with some level of commercial appeal. As explained by Alan Taylor of ALTA Metallurgical Services at the Minerals, Metals & Materials Society's 2013 annual meeting and conference in his paper Laterites: Still a Frontier of Nickel Process Development , the commercially applied processes for low-grade laterites are: • Caron Process – reduction, roast, ammonia leach; • PAL (or HPAL) Process – high-pressure sulphuric acid leach; and • EPAL Process – enhanced pressure acid leach. Taylor sketched the history and pros and cons of each of these methods, not- ing that the Caron and PAL processes are not new, having been developed any- where from five decades (PAL) to nine decades ago (Caron), and that they've had varying degrees of commercial suc- cess. There are, for example, four operat- ing PAL plants in Cuba, Australia, the Philippines and New Caledonia, two more in the commissioning stage in Madagascar and Papua New Guinea, and one under construction in Turkey. The EPAL process was developed by BHP Billiton and installed at Ravensthorpe, Western Australia; operations there were suspended in 2009 and it was later acquired by First Quantum and restarted in late 2011. Overall, each approach has significant issues, some in common with the other processes as well as their own process- specific problems, such as high capital cost (PAL, EPAL), high energy consump- tion (Caron), high acid consumption with certain ore types (PAL), high corrosion and maintenance expense (PAL, EPAL), and process complexity (PAL, EPAL). Other processes have been tested and, in some cases, adopted for projects. These include high-pressure acid leaching com- bined with atmospheric-pressure agitated leaching (PAL + AL) in the case of EPAL at Ravensthorpe, and stand-alone atmospher- ic-pressure agitated tank leaching (AL) at Weda Bay in Indonesia, along with heap ğ in Turkey. Other processes using chloride leaching have been tested but have not been applied to commercial recovery of laterites. Taylor said that more recently, anoth- er approach has emerged—nitric acid leaching of laterites—offering some important potential advantages: • It is applicable to both limonite and saprolite ores. • It offers lower capital and operating costs than PAL. Direct Nickel Ltd. successfully tested its DNi laterite leaching process in a 1-t/d pilot plant, a section of which is pictured above. The plant used feed from PT Antam's Buli nickel mine in Indonesia, where Direct Nickel is consid- ering building a 10,000-20,000-t/y-commercial-scale plant. (Photo courtesy of CSIRO) EMJ_pg86-87_EMJ_pg86-87 7/1/14 2:38 PM Page 86