Kinetics of nickel leaching from low-nickel matte in sulfuric acid solution under atmospheric pressure

Abstract

In the conventional metal extraction process, copper-nickel sulfide ores are generally treated by pyrometallurgical processes, including smelting and converting operation. The purpose of the smelting process is to eliminate most of the iron and to concentrate the valuable metals, such as nickel, copper and platinum group metals, into a low-nickel matte. Then, the remaining iron is oxidized and fluxed for removal as silicate slag in the converting process, and the low-nickel matte is converted into a high-nickel matte. However, a substantial portion of cobalt is also oxidized and converted into the slag phase. Additionally, the subsequent treatment of the high-nickel matte after the grinding and flotation processes is complicated, and leads to the dispersion of noble metals. Usually, the loss of noble metals is about 10% ~ 20%. Direct treatment of low-nickel matte by hydrometallurgical methods instead of the converting process may be a good choice, which will prevent the loss of associated elements, such as cobalt and noble metals. Since copper has a very strong affinity for sulfur, the sulfides of iron, cobalt and nickel may dissolve into the liquid phase (leach liquor) under controlled the acidity of the solution, whereas the cuprous sulfide should remain in the residue. The inert noble metals should concentrate in the cuprous sulfide. However, a large amount of toxic hydrogen sulfide will be released in the leaching process, which can be converted to elemental sulfur by the Claus process. Based on the above considerations, it is possible to develop a method for extracting valuable metals from low-nickel matte and recovering the associated cobalt and noble metals. In this study, the kinetics of the acid leaching process of low-nickel matte under atmospheric pressure was studied. In addition, the effects of the stirring speed, initial sulfuric acid concentration, reaction temperature and particle size on the leaching of nickel were investigated. The kinetic analysis of the leaching data for various experimental conditions indicated that the reaction was controlled by diffusion through an inert porous layer. It was determined that the reaction order was 0.54 with respect to sulfuric acid with an activation energy of 58.3 kJ mol−1.