“Grade Engineering? is an integrated approach to coarse rejection that matches a suite of separation technologies to ore specific characteristics and compares the net value of rejecting low value components in current feed streams to existing mine plans as part of a system-view” (Walters, 2017). Two of these technologies are directly recoverable through screening stages: Natural Deportment and Induced Deportment. The potential for taking advantage of “Natural Deportment” by size following blasting and crushing has been demonstrated for a range of ore types. Simple and low cost screening can in some cases generate a fine product with improved grade and a lower grade oversize which can be directed to leach or to waste.Where an ore body consists of many different ore types, the traditional approach of blending to metal grade will often add to complexity of treatment, which will reduce the effect of “natural deportment” by size.The ore texture (i.e. the arrangement of grains or veins within each rock) within an ore type often suggests that well controlled breakage might be able to improve the recovery of valuable minerals to screen undersize and to further lower the grade of rejected oversize. However, testing this hypothesis would be difficult without having groups of ore particles with different ore texture. SMI-JKMRC has developed a quick, non-destructive process, which uses microwave technology to classify the ore particles into different texture classes. The process involves microwave (MW) heating and selecting the particles by their surface temperature. Magnetic and non-magnetic particles were MW heated separately. For some ore types, the particle temperature after MW heating can be correlated with its texture (and many other properties). In general, non-sulphide gangue interacts much less with MW than minerals of interest. Hence, two or more texture classes can be created by selecting hot and cold groups of particles. This allows each component within a complex ore type to be separately tested for its response to well controlled breakage by impact or abrasion. The response of each component is evaluated. The results provide an indication of what breakage strategies might be applied to enhance grade engineering for a given ore type.If Grade Engineering enhanced by selective breakage can be applied to particular ore types in a complex ore body to reject gangue as it is mined, opportunities may be generated to increase the effective size of a deposit as well as to reduce the cost of comminution.
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