Investigation of Electrochemical Dissolution Mechanism of Chalcopyrite in Choline Chloride-Urea Deep Eutectic Solvent

This study investigates the mechanism of chalcopyrite oxidative dissolution in a 1:2 choline chloride-urea deep eutectic solvent (DES) at 35 °C using electrochemical techniques. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) analyses were employed to elucidate the dissolution mechanism. CV results at scan rates of 5, 20, and 50 mV/s revealed the electrochemical nature of chalcopyrite dissolution in the DES, exhibiting three oxidative peaks within the range of 0.2 to 1.0 V. Kinetic analysis of the CV curves confirmed that the oxidation and reduction reactions are irreversible and diffusion-controlled. Simultaneous interpretation of CV and EIS data indicated that the electrochemical dissolution of chalcopyrite is accompanied by forming a passive layer below 0.75 V, which could be composed of elemental sulfur or metal-deficient sulfides. The oxidation peak A1 occurs c.a. 0.25 V, involving the formation of a passive layer from the electro-dissolution of chalcopyrite. The reactions in A1 potential correspond to forming a mixed-sulfide copper and elemental sulfur. With increasing potential to the 0.5 V range, the complete oxidation of chalcopyrite to copper and iron ions and elemental sulfur film can occur. EIS measurements at 0.5 V show that passive layer formation is minimal, with the surface product being porous sulfur, thereby reducing diffusion effects. However, at potentials above 0.75 V, active dissolution of chalcopyrite occurs, directly transforming into Cu and Fe cations and sulfate anions.