Effect of rheology of grinding efficiency in the laboratory scale continuous classifying mill

Different ores containing soft minerals as the main components were ground in a continuously operating ball mill at laboratory scale. The effect of grinding conditions was studied by changing the solids feed rate, the feed slurry density, the weight of ball charge and the mill rotation speed. The optima of these variables in terms of energy consumption and production rate of fine fractions were determined individually for each tested ore. The grinding efficiency with this mill, equipped with a screen as a grate and a classifier at the discharge end, could be improved by lowering the slurry density to 25% solids by weight, which is significantly lower than traditionally used in laboratory tests or industrial practice.

The flow properties of the mineral slurries in question were studied as a function of percent solids for a better understanding of the phenomena observed in the grinding testwork. The viscosities of the mill discharge slurries were measured with different slurry densities. Tracer tests were conducted with different water/solids ratios in the mill feed for measuring the residence times of bulk solids, various size fractions and water, The maximum discharge rates of slurries from the mill were also measured with various slurry densities. The grinding results are discussed based on the conclusions drawn from these measurements.