THERMAL ANALYSIS STUDIES ON MULTIMETAL SULPHIDES: CHARACTERISATION, ROASTING AND LEACHING

Thermal analysis (TA) studies have been made to understand changes in mineralogy that occur when pure sulphide minerals, single concentrates and different Cu-Zn-Pb sulphide concentrates are heated in air. The observed sequential oxidation behaviour of both the synthetic and natural sulphide minerals is characterised by TA traces that are reasonably reproducible. It is shown that oxidation mechanisms of synthetic analogues during roasting are similar to those of bulk concentrates. The oxidation data thus obtained on sulphide roast products are also found to be useful to characterise some partial leach residues. During ammonia leaching of bulk concentrates, the pyrite grains are practically inert and remain in the leach residue along with oxidated lead compounds and goethite. The TA data for roasting of partially leached samples are compared with those for roasting of untreated feed concentrates. The oxidation behaviour of copper, zinc and lead mineral phases of leach residues is then characterised. The observations are corroborated by chemical phase analysis, X-ray diffraction (XRD) and optical microscopy.