Comminution is an energy intensive process and a significant energy consumer. Hence, substantial economic gains can be achieved from optimal selection and operation of grinding circuits using accurate mathematical models of the grinding process and reliable scale-up techniques. A survey of the existing ball mill modelling and scale-up techniques showed that the suitable models for further development are the multi-segment and perfect mixing models. A review of the single particle breakage tests showed that either the drop weight or the pendulum test could be used to develop a simple but accurate laboratory technique for the determination of breakage characteristics of ores.
Initial single particle breakage studies were carried out using a drop weight apparatus. The results showed that the product size distributions from the breakage of specimens can be described as one parameter, "t", family of curves. The parameter "t" was related to the input energy.
A computer monitored twin pendulum was developed for measuring the energy utilization patterns in single particle breakage. From the twin pendulum tests, the comminution energy which is the energy available to a specimen for breakage can be determined. This comminution energy does not increase in direct proportions to the input energy and its use gives a more consistent description of particle behaviour during the breakage process.
Grinding circuit data and ore samples were collected from nine industrial ball milling circuits. Twin pendulum tests were conducted on specimens from three particle sizes of these ore samples to determine ore-specific breakage distribution functions. The results show that the size distribution parameter "t" is determined by the specific comminution energy and the ore hardness for the range of particle sizes tested.
The data from these ball mills were analysed using the multi-segment model and ore-specific breakage distribution functions. From these results, a scale-up relationship was developed. This relationship accounts for the variation of the performance of industrial ball mills with process variables such as mill diameter, mill length and amount of plus 2mm material present in the mill feed.
The secondary ball mills exhibited constant discharge characteristics. Their performance was also analysed using the perfect mixing model. The breakage parameters were related to the mill power consumption which could be predicted from the ball charge volume and the percentage of solids in the mill feed.