Atmospheric acid leaching of a West Australian lateritic nickel ore and leaching of an Indian chromite overburden ore were found to be much more effective using sulphur dioxide as a reductant. The effects of acid concentration, SO_2 and the catalytic behaviour of Cu(II) during leaching were examined. Aqueous SO_2 alone readily leached cobalt and manganese with little iron, but nickel was leached by the addition of mineral acid in direct proportion to the dissolved iron. Kinetic treatment of the data indicates that the iron dissolution follows a shrinking sphere model. Leaching rates in three different acids were found to be in the order of HCl>H_2SO_4>HClO_4. The difference in acid reactivity appears to be mainly related to the speciation of Fe(II) and Fe(III), E_h of the solution and proton activity. An E_h-pH diagram has been constructed which considers the different species involved during reaction.
展开▼
