An analysis of the influence of grinding aids on the breakage process of calcite in media mills

The effectiveness of calcium stearate, boric acid, and silica as additives for the fine grinding of calcite in media mills, i.e. ball, rod, and vibrat ion mills, were explored, by following the size distribution of the ground product collected at various time intervals from 15 s of grinding up to 30 min, using a single size feed. While calcium stearate could achieve a modif ied grinding rate factor of 1.5 in the ball mill and had indicated an optim um concentration for maximum performance, both boric acid and silica remain ed inert materials without indicating any influence. It was also found that the presence of calcium stearate during the initial stages of, grinding in troduced a retardation effect on the grinding process, with the product bei ng coarser in comparison with the blank sample. To overcome this retardatio n effect for the breakage process induced by the additive, it was found pre ferable to delay the introduction of the additive by around 5 min. Analysis of the breakage process was carried out by estimating the breakage paramet ers using the G-H solution for the size-discretized batch grinding equation . It was found that while the additive reduced the breakage rates of coarse r size fractions during the retardation period, it helped to significantly increase the breakage rates of finer particles during the finer stages of g rinding. The higher breakage rates at finer stages of grinding and the redu ced agglomeration observed during this period indicate the acceptability of the alterations in the flow behavior of the mill charge as the possible me chanism for the additive in media milling.