Fluidized Bed Selective Oxidation-Sulfation Roasting of Nickel Sulfide Concentrate: Part II. Sulfation Roasting
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CURRENTLY, the roasting—electric furnace smelting—converting route is used at two nickel smelters in Canada to treat nickel concentrate to produce a nickelrich matte. The roasters use air to oxidize the sulfides at around 973 K (700 °C), which are then fed to an electric furnace for smelting at about 1573 K (1300 °C). The produced matte is then further oxidized in Pierce-Smith converters. The main environmental issue associated with this route is the emission of SO2 to the environment from the electric furnaces and converters as well as the emission of CO2. To meet future SO2 emission regulations, increasing the degree of sulfur oxidation in the roasters and capturing SO2 from the electric furnace and converters have been proposed.[1] Although such developments will improve SO2 capture, they will not lead to decreasing electric energy consumption or reduced CO2 emissions. In fact, an increase in both is expected. Nickel smelters are also large emitters of many heavy metals into the atmosphere. As an example, in 2004, the Thompson smelter emitted 2.7 t of lead, 3.6 t of arsenic, and 190 t of nickel into the atmosphere.[2] A sulfation roasting process was investigated where the iron sulfides are firstly oxidized to iron oxides followed by selective sulfation of nickel, copper, and cobalt species, eliminating electric furnace smelting and converting. The valuable metal sulfates will then be leached by water or mild acid, purified, and recovered. Since there will be no furnaces to consume electricity nor any need for coke as a DAWEI YU, Ph.D. Candidate, and MANSOOR BARATI, Associate Professor, are with the Department of Materials Science and Engineering, University of Toronto, 184 College Street, Suite 140, Toronto, ON M5S 3E4, Canada. Contact e-mail: dawei.yu@mail. utoronto.ca TORSTEIN A. UTIGARD, formerly Professor with the Department of Materials Science and Engineering, University of Toronto, is now deceased. Manuscript submitted April 24, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS B
reductant, the SO2 emission could be lowered significantly. Since all the gases from the roasters will pass through various gas cleaning steps and then enter a sulfuric acid plant, heavy metal emissions will also be minimal. As a result, the main advantages of the sulfation roasting process are as follows: (1) Eliminating the use of electric energy by the electric furnaces; (2) avoiding the use of coke as a reductant, thereby reducing the CO2 emissions; (3) significant reduction of SO2 emissions; (4) reducing heavy metal atmospheric emissions; and (5) decreasing fugitive emission of gases and dust, and improving workplace conditions. However, the main disadvantage of the sulfation roasting process lies in possibly low recovery of platinum group metals (PGM) from leach solution due to their loss into the leach residue, which requires further investigation. Also, the formation of sulfur trioxide (SO3) during sulfation roasting, and effluent during leaching, require special attention in designing the off-gas handling and water treatment sy
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