Electro-oxidation of sphalerite in weak alkaline sodium chloride solution

The technology of Zn extraction from sphalerite concentrate by using electro-oxidation in weak alkaline sodium chloride solution has been investigated in this paper. The effects of several parameters on Zn recovery during the electro-oxidation have been investigated, and the optimized conditions are listed as follows : pH in the range of 8.5-8.8, NaCl concentration = 3 mol/L, reaction time = 1 h, solid-liquid ratio ≥ 0.03 g/ml, anodic current density = 1342 A/m2, stirring speed = 800 rpm. Under these experimental conditions, sphalerite concentrate can be oxidized efficiently. Furthermore, the electro-oxidation mechanism of sphalerite in weak alkaline NaCl solution has been studied. It was found that the elemental sulfur and the SO42 − were the major existing forms of S from sphalerite and Zn would precipitate in the form of Na2Zn3(CO3)4 in the case where Na2CO3 served as electrolyte pH regulator. To prevent SO42 − from accumulating in the electrolyte and precipitate Zn as Zn(OH)2 instead of Na2Zn3(CO3)4, Na2CO3 was replaced by Ca(OH)2 to stabilize the pH of electrolyte, and the effect of the addition of Ca(OH)2 on Zn recovery was investigated.