Zinc recovery from sphalerite concentrate by direct oxidative leaching with ammonium, sodium and potassium persulphates

The recovery of zinc from sphalerite concentrate by oxidative leaching with ammonium, sodium and potassium persulphates in sulphuric acid media is reported in this investigation. Effects of particle size, reaction temperature, acid concentration, pulp density (PD) and oxidant concentration on zinc dissolution rate were determined. The results showed that leaching of 95% zinc was achieved from the concentrate of particle size -150 mum at a temperature of 333 K for 5 h in the presence of 20% (w/v) ammonium persulphate (APS) with 5% (v/v) sulphuric acid concentration. The best fit of the kinetic data to a diffusion-controlled model indicated that diffusion through the product layer was the rate-controlling step during the dissolution. The activation energy was determined to be 41+/-2 kJ/mol in the temperature range 308-333 K which was also an indication of the diffusion-controlled process. The mechanism of the leaching was further established by characterising the original concentrate and the leach residue by XRD phase identification, optical and SEM-EDS studies. (C) 2002 Published by Elsevier Science B.V.