The Effects of High-Power Microwaves on Comminution and Downstream Processing

Abstract

The incentive for this research was to assess the potential of microwave treatment to fracture ores and improve surface area to reduce comminution energy consumption and improve downstream recovery. Pilot-scale microwave treatment was performed on two ores: a gold ore and a copper-nickel sulphide ore. Three microwave tests were done for each ore: batch tests at low-power (BB) and high-power (BP), and a continuous belt test at high-power (CP). Treatment variables investigated were heating time, microwave power and particle size. Treated ore was then used to assess the impacts on comminution (ore competency and liberation). Additionally, impacts on leaching (gold ore) and roasting (sulphide ore) were studied. Surface area measurements showed improvements for each gold ore treatment; between a 2.5% and 21% increase in m2/g. The sulphide ore reported marginal increases to surface area, although the CP test showed a 7% improvement. While the differential heating improved surface area, comminution energy consumption was unchanged apart from the CP test, which reported a 19% decrease in SAG work index, WSDT. The treatments did not weaken the ore enough to reduce the energy consumption, but still promoted grinding that enhanced surface area. Liberation analysis confirmed this, showing increases to value sulphide liberation, particularly for the high-power tests. Cyanidation showed that enhanced surface area improved the gold recovery. Improvements to gold recovery were proportional to the surface area increases reported. After 6 hours, a 26% increase in gold recovery was reported for the BP test; a 16% increase was reported for the CP test. This confirmed that continuous high-power microwave treatment can improve gold recovery by creating rapid thermal stresses. No significant trend was found between fracture and cyanide consumption. Roasting of the sulphide ore showed no trend with surface area. A lower sulphur content after microwave heating occurred due to oxidation of the sample, prior to entering the roaster. This degree of oxidation from the treatment was proportional to higher heating rates, and showed that the roast of the BP sample was adversely affected. For an industry process with shorter residence times, oxidation from microwave treatment would be less impactful.