A hybrid leaching process to enhance the dissolution of cupriferous micas in the Chingola refractory ore

Abstract The occurrence of copper in the Chingola refractory ore (CRO) is such that it is chemically locked in cupriferous micas of predominantly phlogopite, chlorite and vermiculite within the mica lattice. This renders the copper refractory to conventional atmospheric leaching. A few technically feasible processing methods have been proposed but appear economically unfavourable. This study has proposed a hybrid leaching process consisting of ore agglomeration, acid curing and leaching in fixed bed columns to maximise the leach efficiency under ambient conditions. The experimental procedure involved characterization of the ore, agglomeration tests, acid curing and leaching experiments in fixed bed columns. The objective was to understand the conditions under which copper dissolution can be enhanced by specifically targeting the refractory cupriferous micas. The results showed that agglomeration and acid curing of the CRO material doubled the total copper dissolution from 32% Cu for the unagglomerated and un-cured material to about 60% Cu dissolution for the agglomerated material. Short bed heights yielded marginally higher leach efficiencies and also faster leaching kinetics than tall bed heights. More crucially, the hybrid leaching process successfully dissolved up to 90% of the total cupriferous mica in the ore, which is reported to be difficult to leach under ambient conditions. Towards explanation of the phenomenon, it is postulated that the acid curing step rendered the Cu OH bonds chemically weak which enhanced copper dissolution from the mica matrix. This leads to partial acid decomposition of the silicate structure and dissolution of the metal cations, leaving a siliceous residue. However, sulphides, especially chalcopyrite was difficult to leach under the conditions employed, for which the use of acidified ferric sulphate solution or bioleaching is recommended. This is a significant step towards the development of a practical leaching process to treat the CRO material.