Zinc recovery from franklinite by sulphation roasting

Residues from the zinc roast–leach–electrowin process contain zinc mainly as finely dispersed particles of franklinite. Thus, floatation, sulfuric acid leaching, and alkali leaching are ineffective methods for zinc extraction. An efficient technique was used for the extraction of zinc from hydrometallurgical zinc residues by sulfate roasting of a residue–sulfur–oxygen–H2O mixture followed by water leaching. The effects of various parameters, such as roasting temperature/time, the sulfur amount, leaching time/temperature, and liquid/solid ratio on zinc leaching were studied. Systematic studies indicate that high zinc leaching rate can be achieved under the following conditions: sulfur addition, 1.2 times theoretical value; duration, 2 h; temperature, 250 °C at roasting stage; and room temperature, liquid/solid ratio 4, and duration time 0.5 h at leaching. X-ray diffraction analysis indicates that the zinc-containing compounds convert into water-soluble zinc sulfate after roasting.