Optimum Treatment Time for Solid-State Extraction of Nickel from Nickel Sulfide Concentrates at 1073 K

Solid-state thermal treatment of Ni sulfide concentrates in an inert or reducing atmosphere, and the presence of metallic Fe is proposed as a feasible route to produce ferronickel (FeNi) alloy while retaining S in iron sulfides. The present work investigated the effects of temperature and amount of Fe addition via a thermodynamic analysis, giving a suitable temperature of 973 K to 1173 K and metallic Fe to Ni concentrates mass ratio of 0.5 to 2. The minimum time required for Ni extraction at 1073 K was investigated via thermal treatment experiments of various durations, and it was determined to be 30 minutes. Under the tested experimental conditions, average Ni concentration in the resulting sulfides and the generated FeNi was found to be 0.5 ± 0.2 mass pct and 16 to 18 mass pct, respectively, and in good agreement with the thermodynamic predictions. The maximum Ni recovery to FeNi was approximately 97 pct and the characteristic particle sizes d₁₀ and d₈₀ of FeNi were 14 and 45 µm, respectively. During 360 minutes of the thermal treatment, only 0.7 mass pct of S in the concentrates was released to the off gas as SO₂.