The oxidation of three nickel concentrates from two Canadian smelters was studied by thermogravimetric analysis. Concentrate samples were heated to 1223 K (950°C) in inert or oxidizing atmospheres to determine the reaction behavior. By recording the mass change as well as the SO 2 content in the outlet gas, the oxidation behaviors were quantified. Isothermal roasting tests were carried out on the concentrates over the temperature range of 673 K (400°C) to 1123 K (850°C). When heated in air, the samples gain mass as a result of sulfate formation at temperatures up to approximately 873 K (600°C) to 973 K (700°C), whereas at higher temperatures, the samples exhibit a large mass loss attributed to sulfate decomposition as well as direct SO 2 formation by oxidation. In a 4 pct O 2 gas atmosphere, significantly less sulfates were formed. Mixed reactions take place, in which some lead to mass loss and SO 2 generation, and others lead to mass gain and SO 2 consumption. The relative importance of the various reactions depends on the experimental conditions.
Nickel sulfide concentrates from two Canadian nickel concentrators were investigated to improve the understanding of SO 2 formation and release during processing. The concentrates were heated in gases of various oxygen concentrations up to 1573 K (1300°C) in a thermal gravimetric analysis unit to simulate what may take place during calcine collection and processing. The resulting SO 2 gases were also measured. It was determined that during oxidation, there are competing reactions, such as 3FeS þ 5O 2 ¼ Fe 3 O 4 þ 3SO 2 leading to mass loss, or 2FeS þ 5O 2 þ SO 2 ¼ Fe 2 SO 4 ð Þ 3 causing mass gain. At temperatures up to approximately 973 K (700°C), sulfates were formed readily, whereas at higher temperatures, they would decompose, evolving SO 2 . By lowering the oxygen content in the surrounding gas, the sulfates decomposed more readily. In an argon or hydrogen atmosphere or in vacuum, it is possible to enhance the sulfate decomposition greatly, possibly allowing for reduced SO 2 emissions from the electric furnaces.
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