Leaching kinetics of low nickel matte in an aqueous solution of sulfuric acid saturated with FeSO4 and NiSO4

Abstract

• The oversaturated sulfate solution leaching of low nickel matte was proposed. • Leaching kinetics of low nickel matte in the saturated solution was investigated. • Compared with H 2 SO 4 leaching, the reaction rate in saturated solution was slower. • The nickel dissolution was controlled by diffusion through the inert porous layer. • The leaching kinetic equation is: 1 - 2 x / 3 - 1 - x 2 / 3 = 3.0 × 10 - 2 C 0 3.02 · r 0 - 2 · exp ( - 48741 / R T ) · t . In the previous study of our group, the low nickel matte was leached directly using H 2 SO 4 under atmospheric pressure. As long as the acidity of the solution was high enough, the high-efficiency leaching of iron, cobalt and nickel can be realized. Moreover, the cuprous sulfide and precious metals cannot be decomposed by H 2 SO 4 and were enriched in the leach residue. Due to the high concentration acid used in the leaching process of low nickel matte, the residual acid in leaching solution may need to be neutralized firstly before the subsequent metal separation. However, a lot of alkali will be consumed, resulting in the formation of harmful inorganic salts. In the experiments, we found that sulfate in the leaching solution could reach saturated and continuously crystallized out under the condition of high concentration of sulfuric acid. Based on the above considerations, the crystallization method may be a choice. Upon combination of the leaching and crystallization process, a new way to extract valuable metals and effectively recycle the sulfuric acid was proposed. However, the dissolution of low nickel matte will be also affected when the solution is saturated. Therefore, it is necessary to explore the leaching behavior of low nickel matte in the presence of solutions saturated with sulfate. In this study, the leaching kinetics of low nickel matte in H 2 SO 4 solutions saturated with FeSO 4 and NiSO 4 was investigated. Kinetic data of the dissolution of nickel for various parameters showed best fit to the kinetic model governed by diffusion in the inert porous media. The results shown that the reaction order of H 2 SO 4 was 3.02 and the activation energy of the system was found to be approximately 48.7 kJ·mol −1 . Compared with sulfuric acid leaching, the reaction order of this study increased greatly, which indicated that the influence of acid concentration on leaching process increased. In addition, the decrease of activation energy showed that the oversaturated sulfate solution leaching process was consistent with the internal diffusion control, which may be because the existence of crystal had an effect on the diffusion of H + ions in pores.