The comminution energy-size reduction of the Bond Mill and its relation to Vickers Hardness

Abstract The results of Bond Work index (BWi) tests of five materials with five closing screen size (P 1 ) of 63o 500 µm are documented. These are normalized to eliminate the effect of material present finer than the closing screen sizes and test sample apparent densities. Analysis of normalized test results show, with a correlation factor R 2 of 0.9956, that the revolutions required in all the Bond Work index mill tests conducted (29–419 revolutions) corresponds to a specific grinding energy per Bond Mill revolution of 0.0823 kWh/ton for a material corrected to a tapped apparent density of 1 t/m 3 and for material present finer than the closing screen size. Conversion of this value to operation of the mill for the Bond Work index test results in a value of 194 ∗ 10 −7  kWh/mill revolution. It is demonstrated that the indicated specific grinding energy of the Bond Mill revolution is not a precise value. An exponential function with a perfect correlation is presented relating the final required number of Bond Work index test mill revolutions required with the P 1 values for sample materials tested. A perfect correlation with an exponential relation to the evolution of the specific grinding energy with change in closing screen size is presented. This relation is interpreted as a measure of the reduction in grinding efficiency with increase in fineness of grinding. It also shown that there is an exponential relation with a R 2 correlation factor of 0.9900 between experimental specific grinding energy of a mono-mineralogical material normalized for  1 content and apparent density to the root of its VH at a given P 1 . Most if not all the deviations between the calculated specific grinding energy based on P 1 values and the sample Vickers Hardness correlates with the differences between the experimental and corrected mill revolutions applied to compensate for the  1 fines contents of the test samples.