Role of dispersants in kinetics and energetics of stirred ball mill grinding

Abstract

Rheology of suspensions plays an important role in fine grinding of solids in stirred ball mills which exhibit superior performance in the sub-sieve grinding range than the conventional ball mills, in terms of both throughput and energy consumption. Addition of suitable dispersants to the slurry feed can result in a drastic reduction or even elimination of yield stress and permits higher solid loadings of the pulp. This investigation shows that size distributions of the comminuted products collapse onto essentially identical self-similar or self-preserving curves when particle size is rescaled by the median size, irrespective of the presence or absence of dispersants. The median size therefore is a consistent one parameter index of fineness that drives the size spectrum on its grinding trajectory which remains invariant of solid loadings and dispersant levels. The rate of change cf this characteristic length with the expenditure of specific grinding energy does not seem to vary with the addition of a dispersant. It is therefore inferred that dispersants do not effect the grinding mechanisms operating in the mill and the “speed” of grinding, that is, the inherent efficiency of the mill. However, since the rate of production of fines is directly proportional to the amount of solids present in the grinding charge, dispersants can under favourable conditions enhance the productivity or throughput of the mill significantly. A lumped parameters G-H model of grinding, when formulated in energy expended rather than in grinding time, can accurately simulate the kinetics of grinding in the stirred mill.