Authors: Ali, AY; Bradshaw, SM

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Ali, AY & Bradshaw, SM 2008, 'Effect of Grain Size and Thermo-Mechanical Properties of Minerals on Strength Reduction of Binary Ores Subjected to Microwave Radiation', in Y Potvin, J Carter, A Dyskin & R Jeffrey (eds), Proceedings of the First Southern Hemisphere International Rock Mechanics Symposium, Australian Centre for Geomechanics, Perth, pp. 85-97.

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Abstract:
Previous work has shown that microwave heating of mineral ores induces fracture around grain boundaries due to the differences in absorption of microwaves and the resulting differential thermal expansion among the various mineral phases in the ore particles. As a consequence, this reduces the energy required in subsequent grinding and enhances liberation of valuable minerals. This study investigates, through simulation, the influence of grain size and thermo-mechanical properties of minerals on uniaxial compressive strength (UCS) reduction when binary ores are subjected to microwave radiation. Nine different binary ore models were constructed by randomly disseminating 10% (in volume) microwave absorbing minerals in transparent matrices. Three different grain sizes: coarse-grained, medium-grained and fine-grained were investigated. Computational simulations of heating, thermal damage and UCS tests on the conceptual binary ores have been undertaken by using the package, FLAC. It is shown that in general the thermal properties of the microwave absorbing mineral and the mechanical properties of the transparent matrix have the most significant effect on the strength reduction. Binary ores containing a microwave absorbing mineral that has a high thermal expansion coefficient in a strong transparent matrix achieve higher reductions in strength. The influence of grain size is also quantified, and it is shown that, for the same energy inputs and mineral types, the reductions in strength are much higher in coarse-grained ores. These results are used in conjunction with experimental data, in developing a decision tree which is used for selecting ores amenable to microwave treatment, and in elucidating the practical success or failure of particular ores to treatment. Damage maps showing reduction in UCS as a function of the operating parameters power density and treatment time are used to provide design targets and operating conditions for microwave applicators being developed for industrial application.

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