The effect of screen versus cyclone classification on the mineral liberation properties of a polymetallic ore

Abstract The heuristic of a constant liberation by size independent of the degree of comminution has been established as a robust assumption over time. Therefore, when assessing the comminution circuit performance, achieving a final target P80 size at the lowest possible energy and cost seems to be the only concern. The introduction of higher capacity fine screening to replace hydrocyclones challenges this fixed approach due to the inherent difference in classification principles between the technologies. The impact of classification efficiency and mode on the liberation properties of a polymetallic ore ground in a production ball mill circuit are presented. It was found that the liberation properties remained constant across the comminution device but were significantly different across the circuit. The circuit closed with screens was found to improve the coarse particle liberation in comparison to the hydrocyclones. The liberation data is presented and implications for circuit performance are discussed. It is postulated that the assessment of comminution circuit design and performance should be based on the ultimate objective, recovery of the valuable minerals, and thus be based on the ore- and process-specific recovery window, not on a fixed ‘grind size’.