Short-pulse microwave treatment of disseminated sulfide ores

Theoretical and experimental analyses are used to study the feasibility of using short-pulse microwave energy as a pretreatment step in comminution. Ores of interest contain microwave-absorbing mineral in a low-absorbing gangue. A finite element numerical model is used to predict the thermomechanical response of a single pyrite particle in a calcite host rock during microwave heating. The effects of power density and mineral particle size are presented. Using microwave power densities within those expected in currently available equipment, significant temperature differences are predicted between the pyrite particle and the calcite matrix. Resulting thermomechanical stress exceeds typical strengths of these minerals. Laboratory tests verify rapid, selective heating of crushed sulfide minerals. Tests with mixtures of pure minerals show heating rates directly proportional to the mass of high-loss mineral; thus, shielding of mineral grains by other grains does not appear to be significant. A cursory energy-use analysis suggests that short-pulse microwave treatment can be accomplished with relatively small energy input compared with current energy consumption in comminution. Although improved comminution has yet to be experimentally demonstrated, initial results are promising from both a technical and an economic standpoint.