This paper presents a case study to reduce the operational cost on the secondary ball mill circuit in the Lead/Zinc Concentrator at Mount Isa Mines. The circuit includes two five-metre diameter ball mills each closed with a cluster of ten 15-inch cyclones. The operating cost for both ball mills is about six million Australian dollars per annum._x000D_
The concentrator achieves 75 per cent of the plant design capacity with one ball mill operating, but will have to use two ball mills when 100 per cent plant capacity is required._x000D_
The optimisation study on the circuit identified a new flowsheet that enabled the concentrator to reach 100 per cent of the capacity by using one of the two secondary ball mills. The success of the project utilised the existing equipment rationally and saved the operational cost for one ball mill at full concentrator capacity._x000D_
A further simplified secondary circuit is proposed using the IsaMill for the secondary grinding duty. Performance of the IsaMill circuit and the potential cost savings are predicted.