In order to investigate the mechanism which govern the dissolution of nickel from a matte composed essentially of heazlewoodite and ferronickel, the leaching was carried out in a mixture of HCl, FeC1₃, and FeC1₂.
In about 30 minutes of reaction, ferronickel was almost completely dissolved, and showed a high reactivity to Fe³⁺, with a tendency proportional to the Fe³⁺ ion concentration. The activation energy was about 4.2 kcal/g mole and indicated a low temperature dependence. H⁺ and Fe²⁺ ions were not directly involved in the reaction of nickel matte, and the concentrations of these ions did not exert any significant influence on the dissolution rate. The sulfur layer deposited on the leached particle did not give any internal diffusional resistance for both reactant and product. The rate of dissolution for heazlewoodite was independent of Fe³⁺ ion concentration. The sulfur and the Ni_3-xS₂ having identical crystalline structure with heazlewoodite were formed on the particle, and the value of x was inceased as the reaction proceeded. However, the formation of millerite, an intermediate, was not observed.