D.N. Whittles

Application of numerical modelling for prediction of the influence of power density on microwave-assisted breakage

Abstract The influence of electric field strength on the microwave treatment of ore is elucidated. The ore consisted of a microwave-absorbing mineral in a low-absorbing matrix, and the influence of electric field strength was assessed by numerical simulation. Simulations were undertaken using finite difference modelling techniques for a theoretical 15×30 mm sample of calcite host rock containing 10 vol.%, 1-mm2 particles of pyrite. The simulations modelled the microwave heating, thermal conduction, expansion, thermally induced fracturing and strain softening and, finally, uniaxial compressive strength to predict the effect of microwave heating on the strength of the ore material. Standard correlations were then used to develop specific comminution energy verses t10 relationships for the treated and nontreated samples. It is shown that microwave power density is vital to the fracturing of the rock, and it is suggested that by utilising high power densities, the microwave fracturing of rock to reduce grinding energy requirements may be economically viable.

An investigation into the parameters affecting mass flow rate of ore material through a microwave continuous feed system

An investigation into the characteristics of a gravity-driven conveyor system for passing crushed ore through a microwave cavity has been undertaken using laboratory experiments and numerical modeling. The conveyor system consisted of a vertical hopper, a column passing through the microwave cavity and a tilting vibrating tray. For the efficacy of the microwave treatment of the ore, the residence time of the ore material in the cavity must be known so that the optimum microwave power and exposure time can be calculated, and so that the microwave field can be tuned effectively. The investigation was undertaken using a crushed copper ore from the Palabora mine, South Africa. Four different size fractions and two blends of ore were tested, and the affect of tilt angle and distance between the base of the column and the collector tray were examined. Equivalent numerical models were constructed using discrete element modeling. It was found that the numerical models can be calibrated against the experimental data, and thus can be used to predict flow characteristics, mass flow rates and microwave exposure times which are required in the design of such a conveyor system for microwave pre-treatment.