Effect of microwave radiation on the processing of a Cu-Ni sulphide ore

The need for fine grinding to liberate valuable minerals from low-grade ores has become a major concern due to the high energy requirements and low energy efficiencies of comminution processes. One method being studied to improve efficiencies is microwave pre-treatment. Microwaves can selectively heat certain minerals (absorbers) within an ore, causing internal stresses and forming fractures along grain boundaries. Microwave pre-treatment of an ore containing microwave-absorbing minerals and microwave-transparent gangue can significantly reduce grinding energy. However, these improvements must not be detrimental to downstream processing. This work investigated the effects of microwave radiation on the grindability and flotability of a copper/nickel sulphide ore. A reduction in the Bond Work Index of 22 % was observed after microwave pre-treatment in a 3.0 kW multimodal microwave (2.45 GHz) for 60 s. Although a significant reduction in the required grinding energy was observed, the amount of energy required to treat the sample is significantly higher than the corresponding Bond Work Index reduction, indicating that the process remains some distance from being economically viable. Microwave pre-treatment also showed beneficial effects on the flotation of the ore. Copper recovery remained constant while nickel recovery increased by 33.6 % after 120 s of microwave exposure at 0.8 kW, and by 34.4 % after a 30 s exposure at 3.0 kW. Higher microwave exposure also showed an increase in concentrate grade and flotation kinetics of both copper and nickel.