Fluidized Bed Selective Oxidation-Sulfation Roasting of Nickel Sulfide Concentrate: Part I. Oxidation Roasting
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SINCE the commercial production of nickel from the laterite deposits of New Caledonia in 1875, and later from the great sulfide deposits of the Sudbury district of Canada in 1885,[1] nickel extraction technologies have evolved into several routes. The production of nickel from saprolite (low-Fe laterite) is through reduction in rotary kilns followed by smelting in electric furnaces. The process is highly energy intensive in nature because laterites are not amenable to concentration by physical means and the feed to a laterite smelter contains 35 pct to 47 pct water in the form of free moisture and crystalline water.[2] Limonite and smectite (high-Fe laterite) are treated by high-pressure acid leaching process (HPAL process).[3] Limonite-type laterite is also treated with the Caron process, which comprises pyrometallurgical reduction followed by leaching with aqueous NH3 + CO2 + O2 solution.[3] On the other hand, nickel sulfide minerals are upgraded through efficient and cost-effective milling and flotation,[4] with a concentration factor of about 20.[5] In contrast to laterite smelting, pyrometallurgical processing of nickel sulfide minerals is relatively energy efficient, mainly due to the utilization of energy from the exothermic oxidation of sulfides, as well as the ease of beneficiation of the sulfide ores. As a result, the exploitation of sulfide ores for nickel production has historically exceeded that of oxide ores, despite the geographical predominance of the later.[1] There are two routes for the processing of the nickel sulfide concentrate, namely flash smelting and electric DAWEI YU, Ph.D. Candidate, is with the Department of Materials Science and Engineering, University of Toronto, 184 College Street, Suite 140, Toronto, ON M5S3E4, Canada. Contact e-mail: [email protected] TORSTEIN A. UTIGARD, formerly Professor with the Department of Materials Science and Engineering, University of Toronto, is now deceased. MANSOOR BARATI, Associate Professor, is with the Department of Materials Science and Engineering, University of Toronto. Manuscript submitted April 24, 2013. Article published online October 8, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS B
furnace smelting, both of which produce large quantities of SO2. As a way of mitigating SO2, its fixation mostly in the form of sulfuric acid (H2SO4) is an integral part of the processing routes. Sulfuric acid plants require an optimum SO2 concentration in the offgas to be between 10 pct and 12 pct.[6] Generally, the flash furnace and the fluidized bed roaster produce a continuous offgas stream with suitable SO2 concentration, whereas the offgas released from the electric furnaces and Pierce-Smith converters contains less than favorable SO2 concentrations. The converter emits SO2 into the environment during charging and skimming, which produces a discontinuous flow of SO2 to the H2SO4 plant.[6] In an attempt to lower the environmental footprint of nickel processing, and as an alternative process to treat nickel sulfide concentrate, a two-stage oxidation-sulfation roast
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