Zinc may be directly leached from zinc-lead sulphide concentrates by reaction with sulphuric
PbS(s) + H2SO4 + 1 O2(g) → PbSO4(solid) + S° + H2O 21
ZnS(s) + H2SO4 + 2 O2(g) → ZnSO4(aq) + S° + H2O acid and oxygen. In addition, lead sulphide will be oxidized to give insoluble lead sulphate:
Assume that a plant is to treat 400 t/day of concentrate containing 20.0 weight % Zn as ZnS and 1
10.0 weight % Pb and PbS. The concentrate and leach solution enters the leaching vessel at 32.0% solids. During the leach, 85.0% of the zinc is extracted and all the lead sulphide is oxidized. After the leaching step, the slurry passes to a thickener.
(a) Calculate the concentration of Zn (in g/L) in the solution passing to metal recovery. Assume a solution density of 1.11 g/mL.
(b) Calculate the tonnes per day of elemental sulphur produced.
NOTE: "% solids" is the solids content of a slurry (consisting of particles and solution) and is defined as follows: %solids= (mass of solids)/ (mass of solids+mass of solution)x100.