A help leach feasibility study for mimbula refractory copper ore of Nchanga mine

Abstract

Studies done on Mimbula ore have been on agitation leaching, high temperature and pressure leaching and treatment of refractory ore (TORCO) process. However these methods attracted significantly high capital investment leaving heap leaching as a more economically attractive method to be investigated. This research was aimed at assessing the amenability of Mimbula refractory ore to heap leaching and to understand the conditions under which copper dissolution can be enhanced. The specific objectives were to determine the optimum conditions for agglomeration, the optimum bed height that gave the best leaching efficiency and to establish the relationship between bed height and leaching efficiency. Ore characterisation was done to establish the chemical and mineralogical compostion of the ore. Agglomeration and column leaching experiments were carried out in agglomeration drum and PVC pipes respectively. In order to validate the experiments, each experiment was repeated three times. The soak test, agglomerate size distribution and visual inspection were used as the tools for evaluating the agglomerates quality. For all the column leaching experiments, a chemical and mineralogical composition analyses of feed (ore) and leach residues was carried out in order to measure the extent of copper dissolution. The optimized agglomeration parameters were 600 gpt binder dosage, 14 % moisture content of ore, 20 rpm agglomeration speed and 3 min residence time. Agglomeration greatly improved the leach efficiency and kinetics. The highest leach efficiency of 60 % was obtained with agglomerated ore in 12 days compared to 32 % for unagglomerated ore in 94 days. The mineralogical analysis showed that about 90 % of the cupriferous mica dissolved into solution whilst chrysocolla and pseudomalachite completely dissolved in solution. However, sulphides, especially chalcopyrite were difficult to leach under the conditions employed. It was concluded that Mimbula refractory copper ore is amenable to heap leaching. Further studies to improve dissolution of sulphide minerals using acidified ferric sulphate and/or bioleaching were recommended.