Techno-economic considerations in the commercial microwave processing of mineral ores

Microwave heating of mineral ores had previously been shown to result in process benefits such as reduced strength and improved mineral liberation, but the economics of the process were not attractive and no attention was given to feasible scale-up. This paper provides an overview of the multi-disciplinary approach that has been required to address these failings and develop the technology to pilot scale. Thermal stress simulations show that the operation at high power densities and short residence times is the optimal operating strategy. Experiments using high power densities (approximately 10(9) W/m3 absorbing phase) and short residence times (approximately 0.1 s) were used to confirm that the benefits can now be achieved at economically viable microwave energy inputs (approximately 1 kWh/t). In order to design applicators, reliable measurement of effective microwave properties of crushed ores is required. A method has been developed to extract dielectric properties when the sample thickness is a multiple of half a guide wavelength at some point in the measurement band. Finite difference time domain modeling has been used to design and simulate applicators. A transverse E field applicator with a reflection compensating step has been developed, and a unit with a capacity of > 10 tons/h is being tested. Preliminary economic analysis shows that the overall cost of the process will be between US $0.16 - 0.85 per ton of ore.