Some aspects of nickel extraction from chromitiferous overburden by sulphatization roasting

Nickel bearing chromitiferous overburden of Sukinda region, Orissa, India, was pugged with sulphuric acid and subjected to roasting in two stages. Various operating parameters, such as roasting temperature, time, acid concentration and role of additives were studied. Addition of moisture, during pugging, helped in the formation of insoluble ferric hydroxy sulphate that maintains the equilibrium of SO2/SO3 partial pressure. The double stage roasting improved the nickel extraction over the single stage isothermal roasting of the material at 700°C. An extraction of 85% nickel with 2–3% iron could be achieved at a temperature of 700°C when roasted for 15 mins, 25 wt% sulphuric acid and 20 wt% moisture in two stages. The nickel extraction was improved a further 8–10% by the addition of alkali and alkaline earth metal salts. The role of additives during roasting was also investigated.