Simulation Of Closed-Circuit Mill Dynamics By Locked-Cycle Grinding Of Mixtures

Locked-cycle grinding experiments on mineral mixtures provide a means to study circuit performance in simulated continuous grinding systems. Such experiments with calcite/quartz mixtures revealed that approximately twenty-five 2-minute cycles are required before the composition of the circuit product and the recycle material attain steady state. The circulating load, after steadily increasing during the first 15 cycles, continued to fluctuate over a narrow range. Previous batch ball mill grinding of mineral mixtures has shown that breakage rate functions of minerals are time- independent but composition-dependent. In the closed-circuit grinding of ores with constituents having different grindabilities, the grinding rate parameters for the components also would therefore change during the transient period. With fluctuations in feed composition occurring randomly every half to one hour in processing plants, it is quite likely that the grinding circuit can be in unsteady state perpetually. The significance of these observations is discussed in this paper in the con- text of the models used in control schemes for the grinding circuits