Closed circuit ball mill – Basics revisited

Since the early days, there has been a general consensus within the industry and amongst grinding professionals that classification efficiency and circulating load both have a major effect on the efficiency of closed circuit ball mills. However, the effect of each is difficult to quantify in practice as these two parameters are usually interrelated. Based on experience acquired over the years and the investigative work conducted by F.C. Bond, it was established that the optimum circulating load for a closed ball mill – cyclone circuit is around 250%. This value is used as guideline for the design of new circuits as well as to assess the performance of existing circuits.The role of classification in milling appears to have been neglected in the current efforts to reduce the energy consumption of grinding. Two past approaches, experimental and modelling, for quantifying the effects of classification efficiency and circulating load on the capacity of closed ball mill circuits, are revisited and discussed in this paper. Application to the optimisation of existing circuits and design of new circuits is also discussed, with special attention to the development of more energy efficient circuits.

► Circulating load and classification efficiency effect on ball mill capacity revisited.
► Relative capacity model introduced and validated.
► Relationship between circulating load and classification efficiency verified by industrial data.
► Existing fine screening technology could increase ball mill circuit capacity 15–25%.