Microwave heating of gold ores for enhanced grindability and cyanide amenability

In leaching processes, the mass transport of lixiviants from the bulk of the solution to the site of the mineral of interest is usually the slowest step. Diffusion becomes slower when the particles to be leached are occluded in host minerals. Access to the mineral of interest is enhanced by micro-crack formation within the host minerals as it enhances percolation and migration of lixiviants. Micro-crack formation also augments grinding and allows size reduction and liberation at a lower stress level. In this research, microwave pretreatment was used to augment the grinding of a free-milling gold ore containing quartz, silicates and iron oxides. Under microwave irradiation, selective heating of the different mineral components resulted in thermal stress cracking. Microwave processing enhanced the grindability of the ore, and crushing strength was reduced by 31.2%. The presence of micro-cracks improved leaching rate, and over 95% extraction was achieved within 12 h as against 22 h for the non-microwaved sample. Such a strategy can be used to maximize recovery and man-hours on processing plants.