Leaching Mechanism and Electrochemical Oxidation on the Surface of Chalcopyrite in Ammonia-Ammonium Chloride Solution

The interfacial and electrochemical reactions on the passivation layers of chalcopyrite in alkaline solution was investigated. Fe was selectively leached out prior to Cu to form Fe-oxide and Fe-deficient Cu polysulfide layers in a series of tests. The results of the leaching experiments showed that the distribution of FeOOH and Fe2O3 with respect to depth of the passive layers was inhomogeneous. The composition of FeOOH reached a maximum at the surface (51.28 to 115.38 nm). Additionally, a transitional layer between oxides and sulfides consisting of Fe2O3, Cu sulfides, and Cu1-xFe1-yS2 (around 115.38 nm) exists with a fragile and strippable structure. The electrochemical experiments revealed that the key potential between the passive and trans-passive region is 0.3 V-SCE. In the passive region, the chalcopyrite can be either passive or active depending on how it was brought to that potential. The semiconducting property of the chalcopyrite was demonstrated to exist but has minimal impact on the chalcopyrite leaching process compared to passivation and dissolution. At the trans-passive region, S-0 was found at the potential of 0.4 V-SCE, while sulfides were oxidized to sulfur species after 0.5 V-SCE. (C) 2018 The Electrochemical Society.