Kinetics of dry grinding of industrial minerals: calcite and barite

Abstract

This paper presents the kinetics study of dry ball milling of calcite and barite minerals. The experimental mill used was a laboratory size of 209 mm diameter, 175 mm length, providing a total mill volume of 6001 cm 3, with a total mass of 5.6 kg of steel balls of 46, 26 and 12.8 mm diameter, so as to occupy 20% of the mill volume and with a speed of rotation of 74 rpm. The breakage parameters were determined by using the single sized feed fractions of −850+600, −600+425, −425+300 and −300+212 μm for calcite and −850+600, −600+425, −425+300 μm for barite mineral. The S i (specific rates of breakage) and B ij (primary breakage distribution) values were obtained for those feed size fractions in order to predict the product size distribution by simulation for comparison to the experimental data. As the feed size fractions become coarser, the S i values increase. The highest S i value obtained for calcite was 0.86 min −1 for the −850+600 μm feed fraction, while it was 0.42 min −1 for the −300+212 μm feed when 26-mm ball sizes were used in the mill. The ball size effect was also investigated against the S i values in where the S i value increases when the ball sizes become smaller. The B ij values remained essentially the same for each feeds; the average of φ, γ and β values for all feed sizes of calcite were 0.65, 0.95 and 4.40, respectively. On the other hand, the highest S i value obtained for barite was 0.99 min −1 for the −850+600 μm feed fraction, while it was 0.66 min −1 for the feed size fraction of −425+300 μm when 26-mm ball sizes were used in the grinding mill. The B ij values also remained unchanged for each feeds; φ, γ and β values of barite for the average of all sizes were obtained to be 0.69, 0.81 and 3.94, respectively. The simulations of the product size distributions of both calcite and barite minerals were in good agreement with the experimental data using a standard ball mill simulation program. The slowing down effect was seen in the mill after 4 min of grinding for calcite and after 2 min of grinding for barite.