Abstract:

Chalcopyrite (CuFeS₂) is a primary copper-bearing mineral and a major source of copper in geological ore deposits. However, copper dissolution from CuFeS₂ is often hindered by the formation of a thin passive layer when exposed to acidic oxidizing environments, which limits its leaching efficiency. In this work, the electrochemical behavior of CuFeS₂ was investigated in 0.3M sulfuric acid under natural light, dark (no illumination), and UV (λ = 395–400 nm) irradiation conditions. Electrochemical measurements, including potentiodynamic polarization (PD) and electrochemical impedance spectroscopy (EIS), were performed over a range of temperatures (25, 40, 60, and 80 °C) using a conventional three-electrode setup, all the experiments were conducted in a water jacketed cell to keep temperature controlled and constant. At 25 °C, the results showed that the open circuit potential (OCP) shifted from 0.32 to 0.19 V vs. Ag/AgCl when transitioning from natural light to dark and UV exposure conditions, indicating a modification of the surface electrochemical state under different illumination environments. A reduction in anodic Tafel slope (β_a), from 111.7 to 69.5 mV, was also observed, along with an appreciable increase in passive current under natural light and UV exposure, respectively, suggesting enhanced anodic dissolution kinetics under UV illuminated conditions. Furthermore, PD analyses across the investigated temperature range demonstrated an increase in passive current density (at 0.5 V vs. Ag/AgCl) from 0.024 to 0.137 mA/cm², and 0.050 to 0.156 mV/cm², respectively under dark and UV conditions. Both PD and EIS analysis at room temperature indicated an increased passive current density (at 0.5V vs. Ag/AgCl) under UV irradiation compared to the dark condition. This corresponded to an approximately fourfold lower charge transfer resistance (R_ct) and a threefold lower film resistance (R_p) under UV irradiation relative to that in dark condition. These results indicate that UV illumination promotes more favorable interfacial charge-transfer processes and mitigates passivation effects, thereby enhancing the overall electrochemical reactivity of chalcopyrite.

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Ms. Yibo Zhang