Sulfate Formation and Decomposition of Nickel Concentrates

Nickel sulfide concentrates from two Canadian nickel concentrators were investigated to improve the understanding of SO2 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 SO2 gases were also measured. It was determined that during oxidation, there are competing reactions, such as $$ 3{\text{FeS}} + 5{\text{O}}_{2} = {\text{Fe}}_{3} {\text{O}}_{4} + 3{\text{SO}}_{2} $$ leading to mass loss, or $$ 2{\text{FeS}} + 5{\text{O}}_{2} + {\text{SO}}_{2} = {\text{Fe}}_{2} \left( {{\text{SO}}_{4} } \right)_{3} $$ causing mass gain. At temperatures up to approximately 973 K (700 °C), sulfates were formed readily, whereas at higher temperatures, they would decompose, evolving SO2. 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 SO2 emissions from the electric furnaces.