THE EFFECT OF THE IRON CONTENT OF SPHALERITE ON ITS RATE OF DISSOLUTION IN FERRIC SULFATE AND FERRIC-CHLORIDE MEDIA

Fifteen sphalerite samples having solid solution iron contents ranging from 0.04 to 14.7% Fe were leached at 20-90-degrees-C in both 0.3 M Fe(SO4)1.5-0.3 M H2SO4 and 0.3 M FeCl3-0.3 M HCl media. Linear kinetics were observed for all the sphalerites in both leaching systems. The sphalerite leaching rate increased in a linear manner with increasing iron content. At 80-degrees-C in the ferric sulphate system, the rate, as defined by k = (1-(1-alpha)1/3)/t, increased from 0.38 g g-1 m-2 h-1 to 4.33 g g-1 m-2 h-1 as the iron content of the sphalerite increased from 0.04 to 12.5% Fe; the corresponding values in the ferric chloride system went from 0.26 g g-1 m-2 h-1 to 9.73 g g-1 m-2 h-1. Activation energies in the 39-81 kJ/mol range were observed in both systems. The activation energy decreased as the iron content of the sphalerite increased. The kinetics of sphalerite dissolution are similar in both the Fe(SO4)1.5-H2SO4 and FeCl3-HCl system, and the sphalerite leaching reaction seems to be controlled by charge transfer at the sphalerite surface.