Effect of Non-stoichiometry on the Oxidative Leaching Rate of Ni₃S₂ in Nitric Acid Solutions

Abstract

The oxidative leaching reactions of Ni₃S₂ are interesting connection with a hydrometallurgical treatment of nickel matte as well as complex nickel sulfide ores. However, the stoichiometries of Ni₃S₂ and nickel matte vary over a wide range ratio, because its nickel and sulfur species have deficient character, and thus there still remains an ambiguity in the leaching mechanism.
In this study, the effects of non-stoichiometries on the oxidative leaching of Ni₃S₂ samples in nitric acid solutions are discussed from a kinetic aspect based on leaching rate, stoichiometry of the leaching reaction, measurement of electric properties and analysis of leaching products.
From the kinetic consideration, the following conclusion is obtained. The leaching rate is directly proportional to both the concentration of nitric acid and the surface area of the samples used. The overall reaction of oxidative leaching of Ni_3±αS₂ in nitric acid solutions is controlled by a chemical surface reaction step, and the rate equation is given by the following equation.
−[Ni_3±αS₂]⁄dt=Z·exp(−E_a⁄RT)·A_Ni3±αS2·[HNO₃].