Study on leaching and oxidation behaviors of high-grade nickel matte in ammoniacal solution

High-grade nickel matte is an important intermediate product in copper-nickel smelting. In order to reveal the interfacial reaction mechanism in the oxidation process, the leaching principles and oxidation behaviors of high-grade nickel matte in ammoniacal solution were investigated. Heazlewoodite (Ni₃S₂), chalcocite (Cu₂S), magnetite (Fe₃O₄) and ferronickel (Ni₃Fe) were detected after identifying the high-grade nickel matte samples by XRD, SEM and EDS. The leaching behavior of high-grade nickel matte in an ammoniacal solution was studied under exposure to air and anodic polarization conditions. The changes in high-grade nickel matte surfaces before and after the leaching process were observed by a metallographic microscope, and the composition of the leaching products was analyzed by XPS. The leaching results show that Ni₃S₂ and Cu₂S are oxidized successively, forming an oxide layer on the surface of the initial phase. The contrast experiments of anode polarization between the conical electrode with the working interface of single mineral phase and the multi-phase electrode show that Ni₃S₂ begins to oxidize near 0 V (vs. SCE), decomposing into NiS₂, Ni²⁺ and S⁰, among which NiS₂ further decomposes into Ni²⁺ and S⁰. Meanwhile, Cu₂S Oxidation occurs near 0.3 V (vs. SCE) to generate CuS and Cu₂O, and further oxidation to generate Cu₂O, Cu (OH) ₂ and S⁰ after increasing the potential.