The effect of chemical additives on the electro-assisted reductive pretreatment of chalcopyrite

• An electro-assisted reductive pretreatment was performed on chalcopyrite (CuFeS2).
• The use of complexing agents in pretreatment showed an increase in CuFeS2 reactivity.
• Cuprous, sulfide and ferrous ion complexing agents in the pretreatment were studied.
• Copper extracted from pretreated CuFeS2 was higher than when it was not pretreated.
• The sulfide complexing agent (TEA) was found to promote the greatest Cu extraction.

The oxidative leaching of chalcopyrite demands extreme conditions of temperature and solution potential or non-aqueous solvents because of the formation of recalcitrant passivation layers. Chalcopyrite reduction suffers much less from this phenomenon and therefore could provide a starting point as a pretreatment to facilitate the subsequent leach. However, even though the electro-assisted reduction reactions occur at ambient temperature and pressure, the kinetics are slow, and consequently the power requirements are too high, to compete with conventional technology. A further decrease in passivation for a given reduction time should enhance the formation of chalcocite and metallic copper, which should result in an improved copper extraction in the subsequent oxidative leaching stage. This would directly impact the economy of the process.The use of complexing agents for iron(II), sulfide and copper(I) in sulfuric acid solutions increased the amount of chalcocite and metallic copper formed in the electro-assisted reduction pretreatment of chalcopyrite compared with the same leaching system with only H2SO4. The improvement in the copper extraction in the subsequent oxidative stage is probably due to the complexation of iron by the carboxylic acids and sulfur by the ethanolamines in the reductive pretreatment, thus avoiding the formation of a pyrrhotite (FeS) passivation layer on the chalcopyrite surface. On the other hand, ethylene glycol stabilizes copper as the cuprous ion, facilitating the chalcopyrite transformation and copper extraction; however, this action alone is not as effective as the carboxylic acids and the ethanolamines in diminishing passivation.