A method to evaluate the impact of stockpile size segregation on the performance of SAG mills

Semi-autogenous mills in general are fed from a coarse ore stockpile. Providing a uniform feed from the stockpile is essential to maintain a stable performance of the SAG mill and consequently downstream equipment. However, due to size segregation in stockpiles, the particle size from stockpile draw points can vary. The size distribution of feed to the SAG mill could change over the time depending on which feeders are running, the location of feeders, and the level of material at different section of the stockpile. Therefore, simulation of stockpile and SAG mills without incorporating size segregation will not accurately represent the operational performance of grinding circuits because in reality particle size distribution varies over time. A model of a stockpile that incorporates size segregation is presented. This model can be used to simulate different feeding conditions from the stockpile to the SAG mill and provide an opportunity for optimization. The simulation result!s are compared to experimental data from a small-scale stockpile tests in different situations. The results of the stockpile simulations have been used to evaluate the performance of the SAG mill using JKSimMet. Comparison with steady-state data shows the impact of size segregation in stockpiles on the performance of the SAG mill. The results illustrate that the size segregation of stockpile will increase the throughput variance by 404% over 100h of operation. In this example, simulation results indicated that implementing a control strategy to maintain the size distribution of the feed to the SAG mill will increase the throughput by 922 t/h. This paper demonstrates the need for dynamic models of stockpile and materials handling with size segregation to quantify the impact of size segregation on performance of grinding circuits.