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. Var ious operating parameters, such as roasting temperature, rime, acid concent ration and role of additives were studied. Addition of moisture, during pug ging, helped in the formation of insoluble ferric hydroxy sulphate that mai ntains the equilibrium of SO2/SO3 partial pressure. The double stage roasti ng improved the nickel extraction over the single stage isothermal roasting of the material at 700(degrees)C. An extraction of 85% nickel with 2-3% ir on could be achieved at a temperature of 700 degreesC when roasted for 15 m ins, 25 wt% sulphuric acid and 20 wt% moisture in two stages. The nickel ex traction was improved a further 8-10% by the addition of alkali and alkalin e earth metal salts. The role of additives during roasting was also investi gated. (C) 2000 Elsevier Science Ltd. All rights reserved.