Study On Ammonia-Ammonium Leaching Of Low Grade Nieckel Ore With High Alkali Gangue Content

As the rich nickel ore has beening exhausted, the high efficient exploitation of the abundant low-grade resource becomes very urgent. In this paper, the NH₃-(NH₄)₂SO₄-H₂O leaching system is brought forward for treating jinchuan low-grade complex nickel ore, based on the characteristic of its high alkali gangue content. The aim of the study is to explore a feasible way to the treatment of low grade nickel ore.On the aspect of theoretics, the hydrometallurgy thermodynamics of nickel in the system of NH₃-(NH₄)₂SO₄-H₂O is studied thoroughly with MATLAB. By establishing model and calculating on the dissolvability,oxidation potential of nickel ore, It is found that the dissolvability of nickel oxide increases as the concentration of NH₄OH and (NH₄)₂SO₄ increase; the oxidation potential of nickel sulfide decreases firstly sharply then slowly as the concentration of NH₄OH and (NH₄)₂SO₄ are increasing. The study on the thermodynamics about the ammonia reactions of 2NiO·SiO₂ have indicated that the Gibbs Free Energy of those reactions are all higher than zero under normal and high temperature so that reactions can not take place.Based on the analysis of thermodynamics and mechanism of leaching process ,the influences of several factors on extraction rate of nickel from the ores were experimentally investigated in the process of normal and high pressure leaching, such as varieties of oxidant,concentration of lixivium,NH₃/(NH₄)₂SO₄(molar ratio),liquid/solid ratio,particle size,leaching time,temperature, and so on. The results show that the leaching rates of nickel are 42.86%,70.86% under the optimum conditions of the two different systems, respectively. The phase analysis of leaching residues confirms that nickel silicate can not be dissolved, which is the main reason for low leaching rate.