ROLE OF DISPERSANTS IN KINETICS AND ENERGETICS OF STIRRED BALL MILL GRINDING

Rheology of suspensions plays an important role in fine grinding of so lids in stirred ball mills which exhibit superior performance in the s ub-sieve grinding range than the conventional ball mills, in terms of both throughput and energy consumption, Addition of suitable dispersan ts to the slurry feed can result in a drastic reduction or even elimin ation of yield stress and permits higher solid loadings of the pulp. T his investigation shows that size distributions of the comminuted prod ucts collapse onto essentially identical self-similar or self-preservi ng curves when particle size is rescaled by the median size, irrespect ive of the presence or absence of dispersants. The median size therefo re is a consistent one parameter index of fineness that drives the siz e spectrum on its grinding trajectory which remains invariant of solid loadings and dispersant levels. The rate of change of this characteri stic length with the expenditure of specific grinding energy does not seem to vary with the addition of a dispersant. It is therefore inferr ed that dispersants do not effect the grinding mechanisms operating in the mill and the ''speed'' of grinding, that is, the inherent efficie ncy of the mill, However, since the rate of production of fines is dir ectly proportional to the amount of solids present in the grinding cha rge, dispersants can under favourable conditions enhance the productiv ity or throughput of the mill significantly. A lumped parameters G-H m odel of grinding, when formulated in energy expended rather than in gr inding time, can accurately simulate the kinetics of grinding in the s tinted mill.