The recovery of copper and zinc from a sulphide concentrate using sulphate roasting, acid leaching and solution purification

Sulphate roasting has long been known and used industrially to transform metal sulphides into calcines suitable for hydrometallurgical treatment. The thermodynamics of the process are briefly reviewed, and the major parameters governing the rate are outlined. Sulphate roasting was applied on a laboratory and small pilot plant scale to a copper-zinc sulphide concentrate. After sulphate roasting in open-hearth or fluidized bed furnaces, the calcine was leached in mild sulphuric acid solutions. Recoveries of 99% and 95% were achieved for copper and zinc respectively, with little iron contamination. Gold and to a lesser extent silver were recovered by cyanidation from the leach residues. Various methods were considered for the purification of the leach solution and the recovery of copper and zinc from the purified solution: a most attractive appeared to be a co-extraction of iron and zinc with D2-EHPA, followed by crystallization of copper sulphate from the purified solution.