Thermodynamic assessment and experimental study of sulphidation of ilmenite and chromite

This study provides an assessment of the high temperature thermochemical reactions of ilmenite and chromite with sulphur and uses the information to analyse the possibility of selective sulphidation of chrome-bearing spinels as a new route for chromite removal from ilmenite concentrates. The work includes both systematic thermodynamic assessment and targeted experimental investigations. Thermodynamic calculation results studying the effect of reactants composition, temperature and different sulphur sources (H2S and elemental S) showed that chromite can be selectively sulphidised at a controlled atmosphere of partial pressure of oxygen (pO2) below 10−10 atm and partial pressure of sulphur (pS2) above 10−6 atm. The addition of carbon with sulphur was found to be useful for the chromite sulphidation reaction. The optimum quantity of sulphur reactant to carbon was found to be 3 : 1 (in mole) for 1 mol of chromite. Sulphidation experiments on a mixture of natural ilmenite and chromite at 1100°C for 5 h using 5%H2S as a sulphur source showed that the ilmenite was preferentially sulphidised first, which was also in a good agreement with the thermodynamic assessment. Sulphidation of a naturally occurring chrome spinel contaminated ilmenite concentrate showed that the degree of weathering also played a role in the sulphidation of the chrome spinel. It was also concluded that H2S is not suitable for selective sulphidation of chrome spinel from the ilmenite concentrate and that tightly controlled pS2 and pO2 conditions are required.