The Effect of Dissolved Copper and Silver on Sphalerite Dissolution in Ferric Sulphate-Sulphuric Acid Media

摘要

The dissolution rates of low-iron Santander (0.08 % Fe) and Oklahoma (0.2 % Fe) sphalerites, defined by l-(l-a)~(1/3) = kt, increase rapidly as the dissolved copper concentration of the 0.3 M Fe(SO_4)_(1.5)- 0.3 M H_2SO_4 leach solution increases from 0 to about 100 mg/L. The rates then increase slightly, or remain nearly constant, as the copper concentration rises to about 500 mg/L. Further increases in the copper concentration, to 5000 mg/L, cause the rates to decrease. For the high-iron Montauban (8.0 % Fe) and Kenabic Lake (10.4 % Fe) sphalerites, the leaching rates decrease dramatically as the Cu concentration increases from 0 to about 20 mg/L, but then essentially stabilize at a very low level for dissolved copper concentrations up to 7500 mg/L. Detailed SEM-EDX study of the reacted sphalerites detected only sphalerite and elemental sulphur. Copper sulphides were not detected, in agreement with the fact that the dissolved copper concentration remained essentially constant throughout the experiments done in the presence of the ferric sulphate oxidant. Dissolved silver concentrations in the 0 to 10 mg/L range effectively suppress the dissolution of both low-iron and high-iron sphalerite. A dissolved Ag concentration of only 1 mg/L almost entirely suppresses the leaching of low-iron sphalerites, whereas a concentration of 2 or 4 mg/L is needed to produce a similar effect for the iron-rich Montauban or Kenabic Lake sphalerites. SEM-EDX studies of the reacted low-iron and high-iron sphalerites confirmed the inhibitory effect of dissolved silver. A few particles of silver sulphide were detected on the sphalerite surfaces or embedded in sulphur globules, but there was no evidence of a continuous passivating silver sulphide film. Thus, the dissolved silver must either form an adsorbed monolayer on the sphalerite or somehow alter the electronic properties of the sphalerite surface as seems to be the situation for dissolved copper.