Surface oxidation using chlorine dioxide for cuprite and its oxidation leaching mechanism in sulfuric acid solution

Abstract

Cuprite (Cu2O) is difficult to directly leach in acidic solutions. In the absence of oxygen, the acidic leaching process of cuprite occurs via a disproportionation reaction and can achieve a maximum cuprite leaching rate of only 50%. Furthermore, to improve the copper leaching rate, Cu(Ι) in cuprite must be oxidized via electrochemical reactions. In this study, chlorine dioxide (ClO2), a novel environmentally-friendly oxidant, was used to oxidize cuprite to enhance the leaching effect in sulfuric acid (H2SO4)solution. Leaching experiments, electrochemical measurements, atomic force microscopy (AFM), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were used to analyze the oxidation leaching mechanism of cuprite under different reaction conditions. Under the condition of a leaching temperature of 50 °C, sulfuric acid concentration of 0.14 mol/L, average particle size of 60 μm, stirring speed of 800 rpm, and leaching time of 30 min, the leaching rate of cuprite reached 90.18% after adding 0.07 mol/L of ClO2. Electrochemical measurements demonstrated that a higher ClO2 concentration increased the corrosion rate of cuprite and oxidation efficiency. Moreover, the surface characterization results showed that with the addition of ClO2, monovalent copper on the cuprite surface was oxidized to divalent copper, which promoted the acidic leaching process of cuprite. In addition, once the cuprite surface was oxidized during oxidation leaching, sulfuric acid leached this layer until the end of the leaching process. The DFT calculation results further proved that with the participation of ClO2, the leaching reaction of cuprite in an acidic solution was more likely to occur. This oxidation leaching method might provide a reference for the effective leaching of cuprite.