The performance improvement of a full-scale autogenous mill by setting the feed ore properties

The feed ore properties can seriously affect the success of autogenous (AG) mill operation in terms of many criteria such as production rate, product quality and energy consumption, since the grinding media in an AG mill derive from the feed ore itself. In this research, the feed ore properties including hardness and particle size distribution was applied in order to improve the AG mill operation. In the regard of particle size distribution, the amount of materials coarser than 200 mm in the feed of a full-scale AG mill was increased by direct addition large lumps of ore (200–500 mm). Accordingly, the mill power consumption decreased from 8.4 to 5.16 kWh/t (a nearly 40% reduction), and the fresh feed flow rate increased from 515 to 615 t/h (a nearly 20% increase in the mill throughput) by increasing the amount of materials coarser than 200 mm in the AG mill feed from less than 10 wt% to about 30 wt%. In the regard of feed ore hardness, the blending of two hard and soft iron ores was performed at various blend ratios. Tracking the mill performance showed that the mill power consumption decreased from 9.49 to 6.63 kWh/t (a nearly 30% reduction), P80 of the mill product decreased from 611 to 355 μm, and the mill fresh feed flow rate increased from 511 to 521 t/h by decreasing the feed ore hardness from 112 min to 58 min based on SAG power index (SPI). Finally, a model was developed for the prediction of mill power consumption.