Optimisation and better control of milling circuits require extensive modelling of milling data. This paper
extends the enquiry to the use of the attainable region (AR) technique to determine the optimal residence
time of ore in a ball mill. It also evaluates the energy requirements of the mill at the set residence time to
maximise the production of the desired size range which enables maximum recovery of platinum group
minerals (PGM) during the flotation stage.
With these purposes in mind, the breakage function and the scaled-up selection function parameters
were used to simulate the operating conditions required by an industrial ball mill and the power requirements
were predicted using the Morrell power model. This allowed the application of the AR methodology
to be extended to a full-scale ball mill. Then a link was established between residence time to mill
product specifications for a given feed size.
The findings showed that the residence time required by a full-scale mill falls between those at which
the fully mixed and the plug flow mills operate. The results also showed that operating the ball mill at a
lower mill speed and a higher ball filling saves energy. Mill speed was again found to be a key operational
factor for controlling the retention time of particles inside the mill. This yielded valuable insight for the
importance of optimally controlling both the residence time of the material inside the mill and the
amount of energy required to maximise the desired size range, in this case 75 + 9 lm.