Enhanced dissolution of minerals: Microtopography and mechanical activation

A theoretical evaluation of the role of microtopography in the phenomenon o f mechanically activated dissolution of finely milled minerals has been und ertaken. Attention was directed to the role of surface steps produced by fr acture and abrasion of milled particles. It was estimated that the activati on energy for dissolution at the edge of steps is at least 20% less than th at for dissolution from terraces (flat regions) between the edges, leading to enhanced dissolution of steps. The relative rates of dissolution at step s and terraces depend upon the particular mineral/solution process chemistr y through the effects of process temperature (T) and the magnitude of the a ctivation energies for dissolution. Enhanced dissolution of particles conta ining stepped surfaces was modelled by including the fraction, alpha, of di ssolution sites on step edges relative to the total number of surface disso lution sites. The fraction, alpha, is expected to be mineral-sensitive thro ugh the effects of fracture and cleavage behaviour on step formation. The m ean diameter, D-M, of particles subject to enhanced dissolution by microtop ography factors was shown to lie in the micron (mu m) to sub-micron range. This range is consistent with particle sizes where enhanced dissolution by mechanical activation has been reported. (C) 1999 Published by Elsevier Sci ence Ltd. All rights reserved.