Short Course Treatment of Nickel-Cobalt Laterites July 2017 ALTA Metallurgical Services, Melbourne, Australia www.altamet.com.au
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SHORT COURSES Course Outlines Ore Characterization and Process Implications Idealized Orebody Profile Real Orebodies Metallurgical Implications Treatment of Nickel-Cobalt Laterites Commercial Treatment Processes Pressure Acid Leaching Reduction Roast-Ammonia Leach (Caron) Process Smelting Processes Ferronickel and Matte Smelting Nickel Pig Iron Smelting Processes Under Development Heap Leaching Atmospheric Agitated Tank Leaching - Sulphuric Acid Leaching - Chloride Leaching - Nitric Acid Leaching Segregation Roasting Previously Proposed Processes Sulphation Roast Republic Steel Process Aqueous Chlorination Process Laterite Project Development Project Development Program Scoping Phase Prefeasibility Phase Final Feasibility Phase Pilot Plants Environmental Aspects Case Histories Moa Bay PAL Coral Bay (Rio Tuba) PAL Yabulu Reduction Roast-Ammonia Leach Cero Motoso Ferronickel Smelting PT Inco Matte Smelting www.altamet.com.au
Notes 1. Nickel and cobalt can usually be solubilized from laterites using sulphuric acid at atmospheric pressure, just below boiling point. However, this generally requires a massive quantity of acid, which can render the process uneconomic. The main reason for this is that for limonitic ores in particular, the very high iron content must be dissolved in order to solubilise the nickel. 2. At high pressure and temperature, above 200 C, most of the iron is reprecipitated as hematite, and sulphuric acid is regenerated. Aluminium, another acid consumer, is also largely reprecipitated. Both of these mechanisms contribute to a large reduction in net acid consumption. This leaves magnesium as the main acid consumer, though aluminium can also be a significant contributor. Thus, the magnesium content is generally a major factor in determining whether pressure acid leaching is likely to be economic. For a Moa Bay type project, the historical view has been that the upper limit would be about 3% Mg. However, it varies on a project to project basis depending on the cost of acid, the nickel and cobalt contents and the metal prices. The maximum economic magnesium level would increase for higher grade ores 3. Another major contributor to acid consumption is the acid content of the leach discharge solution. The optimum level is affected by a number of interacting factors, including leach kinetics, metals extraction and hydrolysis reactions. Typically it is in the range of 30-40 g/l. At Moa Bay, this amounts to about one third of the total acid addition. Utilization of this acid to preleach high magnesia ore was one of the main features of the Amax and NICAL Processes, and more recently the Ravensthorpe EPAL Process. This makes it possible to economically treat laterites with higher magnesium levels such as saprolites. 4. A reductant, typically sulphur, is commonly added as required to promote leaching of manganese minerals and release cobalt and to supress the formation of chromium (VI) which would cause problems in downstream processing. Sample Pages Treatment of Nickel-Cobalt Laterites 30
Notes 1. Sequential cobalt and nickel SX circuits both operating on full PLS flow. 2. Mixer-settlers were Bateman reverse flow type. Sample Pages Treatment of Nickel-Cobalt Laterites 97