Flotation of a copper-cobalt sulphide ore: Quantitative insights into the role of mineralogy

Abstract

Cobalt is mainly produced globally from Cu-Co sediment-hosted deposits in the Democratic Republic of Congo. As mining operations progress, oxidic supergene mineralisation gradually depletes, and many have been or are shifting towards extracting sulphide ore at depth. Overall, copper recovery is consistently higher than cobalt, but no in-depth investigation has been conducted to determine if this difference is due to ore mineral characteristics. The role of ore mineralogy on the flotation performance of copper-cobalt sulphides was studied by tracking the changes in mineral properties with time throughout the flotation process. A series of laboratory rougher-scavenger flotation experiments were carried out using a dithiophosphate collector to define the optimum collector dosage, which was determined to be 30 g/t. With that dosage, an experiment was carried out during which concentrates were collected at distinct times and then analysed by QEMSCAN®. The feed ore was relatively rich containing around 32 wt% bornite, 8 wt% carrollite and under 1 wt% of chalcocite and chalcopyrite. The particle size distributions of carrollite and bornite were suitable for flotation while chalcopyrite and chalcocite were relatively fine-grained. Carrollite also showed to be well-liberated while only half of the bornite showed to be fully liberated with around 25 % of bornite in the feed associated with magnesiochlorite, quartz or other gangue minerals. Even though carrollite had favourable properties for flotation, higher recoveries were obtained for bornite, chalcocite and chalcopyrite throughout the whole experiment. Carrollite grain size seems to have played a significant role in the recoverability of cobalt as the optimum size range was relatively narrow compared to bornite at around 20–45 µm with limited recovery above 100 µm. This upper size limit may be increased to some extent with higher collector dosage but, at ambient pH, the differential reactivity of the copper and cobalt sites at the mineral surface favours collector adsorption on copper sites.