Nkwanyana and Loveday (2017) used batch tests in a 0.6m diameter mill to test partial replacement of balls for secondary grinding by rounded pebbles from a SAG mill. At the optimum pebble content of 25% by volume, a 25% saving in ball consumption and a 12% reduction in power consumption was achieved, with no loss in grinding capacity. These very encouraging results were discussed with operators and designers of SABC circuits.This paper compares a 25% pebble/ball composite charge to ball-milling, under conditions typical in large SABC circuits. Concerns about accumulation of 'scats' have also been analysed. All the experiments in this phase were conducted on a silicate ore, with a feed top size of 19 mm, using mill speeds of 75% and 80% of critical speed and balls up to 75mm. The pulp volume in some tests was increased, to simulate an overflow ball-mill. The product size distribution from tests with a composite charge, particularly the fraction of material passing 75μm, was virtually identical to that of the corresponding ball-milling tests. The average saving in power consumption was about 14% and a saving in ball consumption of 25% applies. The solution of the 'scats problem' is discussed.
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