The development of control systems for gold ores grinding circuits has been underway for many years and practically every gold mill in operation today has implemented to varying extents, a control system. These control systems range from simple feed rate water /ore ratio control, to far more complex, optimum seeking methods which attempt to achieve grinding circuit peak efficiency by modulating mill operating variables to maximize some selected performance index, such as mill throughput. In this light, it might appear that grinding circuit control practices are relatively well established and that many users have measurably increased plant profits by applying automation. However, this has not happened all the time in several gold operations. Cases where significantly higher throughput has been realized, for example, as the direct result of automatic control are more exception than rule.
The idea that gold grinding circuits are difficult to control becomes apparent when the profit generating potential of a successful throughput oriented grind control is computed. Gold plant profits can be improved when the productivity of existing grinding equipment can be increased. The difficulties associated with the continuous measurement and control of flow rates, slurry levels, densities and size distribution made control of the grinding circuit a difficult task to accomplish. Today, the sensor problems have been solved for the most part and the operation of the grinding circuit can be enhanced.
Grinding control objectives at gold mills are oriented towards increased treatment rates with optimum particle size for the recovery process (i.e. flotation, leaching, gravimetric concentration). The relatively low gold content of the ores and ever-rising operating costs needs more and more efficient utilization of the available grinding power. In addition, to meet the demands of planned increases in plant capacity, it is very important to reach maximum throughputs in the existing mills in order to minimize capital cost of new grinding units. Superimposed upon these tonnage objectives is the need to maintain gold recovery process feeds at a preselected, constant grind size. This is important because a different size may be desired for the several distinct gold ore types milled.