Control of sulphur oxides emission during the roasting of lime-coated metal sulphide pellets

A promising method for controlling sulphur oxides emission during the roasting of metal sulphides is with the use of lime-coated sulphide pellets. The roasting of lime-coated zinc sulphide concentrate pellets in air at temperatures between 700 and 800°C is investigated. The experimental data show that these pellets have a very high sulphur retention capability, close to 100% up to approximately 60% sulphide conversion. The concentrate pellet size has no significant effect on sulphur capture. Lowering the temperature in the range investigated and using excess lime improve the sulphur capture without a significant adverse effect on the roasting rate. The sulphur emissions at higher sulphide conversions are primarily attributed to cracking of the lime coating. Preliminary data show that cracking can be reduced by increasing the water content of the initial lime.