Simulation of wet ball milling of iron ore at Carajas, Brazil

Laboratory-scale batch grinding tests were performed on 2 sieve size fractions of the almost pure hematite mined at the Carajas mine of CVRD Brasil. Good first-order kinetics of grinding were obtained, both for dry grinding and for grinding with water, using the Bond test levels of ball load and powder load. However, the primary breakage distribution functions were not dimensionally normalized, as smaller particles produced proportionally more fines on primary breakage, possibly due to internal porosity of the ore. The test results were scaled to the conditions of a pilot-scale mill in normal closed circuit, and a ball mill simulator was used to predict the capacity, circulating load and size distributions, employing the size selectivity values calculated from the balance around the hydrocyclone. The simulation results were in reasonable agreement with the observed values. The technique was then extended to predict the behavior of a full-scale mill at a capacity of 308 metric tons/h and a circulating load of nearly 600%. Agreement between simulated results and plant test results was reasonable except that the simulator predicted a product (overflow) size distribution with a higher sharpness index than observed. The reason for this discrepancy is not known.