THE OXIDATION OF SULFIDE MINERALS

The literature associated with the thermal behaviour of mineral sulphi des has been selectively and critically reviewed. Particular attention has been paid to: the importance of characterising the starting mater ial, as well as intermediate products the effect of experimental varia bles on the thermal analysis results The various reactions that sulphi des can undergo in inert and oxidising atmospheres are presented. Unde r mild oxidising conditions, such as an air atmosphere and heating rat es of 10-20 degrees C min(-1), the oxidation occurs as a sequence of r eactions usually controlled by oxygen diffusion, although in some situ ations decomposition of the sulphide with evolution of sulphur can occ ur. Besides the formation of oxides and sulphates, and the subsequent decomposition of the latter, solid-solid reactions can occur between s ulphates and unreacted sulphides. In ternary systems, such as the iron -nickel sulphides, considerable ion diffusion can take place. Under mo re vigorous oxidising conditions, such as an oxygen atmosphere with a heating rate in excess of 40 degrees C min(-1), some sulphides can be ignited. Under these conditions the relative ignition temperatures of sulphides can be measured, and the effects of variables such as partic le size and stoichiometry on the ignition temperature examined. The ox idation of pyrite is presented as a case study of the effects of exper imental variables on the results of thermal analysis. The application of the results of studies to the industrial processing of sulphides of economic importance has been discussed. (C) 1997 Elsevier Science B.V .