Selective sulfation roasting of Ni concentrate to minimize off-gas pollution

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This project aims at developing a new and more environmental friendlyprocess to treat nickel sulphide concentrate. Today, concentrate is sent to nickel smelters where it is oxidized with air to release SO2 and form a solid nickel calcine. This calcine is then sent to electric furnaces for smelting at veryhigh temperature, beforebeing further oxidized in converters emitting SO2. The two nickel smelters in Canada that use this process emit large amounts of SO2 and CO2, and consume significant amounts of electricity.Inthe process to be investigated, the aim is to eliminate a large amount of off-gas pollution from nickel smelters. It is proposed to develop two-step roasting with the first roaster forming iron oxides and the second roaster forming nickel, copper and cobalt sulfates. The valuable metal sulphates will then be dissolved in an aqueous solution, followed bypurification, separation and recoveryof metallic nickel, copper and cobalt. If thiscan be done, the environmental impacts and electric energyconsumption of nickel smelting will be greatly lowered.Incollaboration with Vale-Inco and Xstrata Nickel, a test program will be developed and carried out. Industrialsamples will be collected and characterized with the help of plant personnel. The main focus of the laboratory tests will be to determine how to first selectivelyoxidize the iron sulfides to iron oxides, then to sulphate the valuable metal sulfides. To do this, it is expected that a two-step roasting operation with different temperatures and gas compositions are required. The main technical challenge seems to be that a dense shell of nickel sulphate mayform around each particle, making it difficult for gases to pass through, effectivelyslowing down the reactions. We will studythis possible phenomenon and evaluate various methods to counteract this problem. The results will be evaluated continuouslyand if positive, lead to pilot-plant testing on a larger scale