Unraveling the Chloride Penetration Dissolution Mechanism of High-Grade Nickel Matte During Anodic Oxidation

The beneficial effect of chloride on the leaching of nickel matte by sulfuric acid has been found in hydrometallurgy, but its mechanism has not been properly revealed. This investigation focuses on the analysis of the reaction process of electrochemical oxidation leaching of high-grade nickel matte in HCl solution. According to the condition of potentiostatic polarization, the reactions took place in four stages to obtain different interface reaction products, and the dissolution mechanism has been proposed according to the characterization results. The results showed that the product layer became cracks and porous due to the penetration effect of chloride in the interfacial reaction, which greatly increases the surface area of the interfacial product layer. This makes the interface reaction more likely to occur, thus improving the leaching effect. Accompanied by the dissolution of nickel and copper ions from the high-grade nickel matte, and the sulfur element, which is combined with the metal ions, is oxidized by potentiostatic polarization to form a monosulfide/disulphide (0.2–0.8 V), polysulfide/elemental sulfur (0.8–1.0 V), and thiosulphate/sulfate (1.0–1.2 V). These can provide some constructive guidance for optimizing the existing nickel matte leaching process.