The regrinding circuit is included in a gold concentrator to liberate gold bearing minerals. The optimization is important due to the greater economic return will result thereby than is obtainable at any fineness of primary grind without regrinding. It is possible to define the optimum regrind as that regrind which in conjunction with the optimum primary grind results in the greatest economics return. From the standpoint of plant design, the factor that influences the fineness of regrind in most cases is the fineness of dissemination of gold bearing minerals in the rougher concentrate or middling particles.
The cost of transportation of concentrate to the subsequent processing stage and the economics of the method of concentrate treatment are important factors in operation and must be determined at what point on the optimum grade-recovery curve the regrinding circuit is operated. The function of the regrind design is not to establish this point of operation, but rather to provide the regrind capacity required to permit operation at any reasonable point along the optimum grade-recovery curve. Unlike in primary grinding of low grade gold ores, the economic optimum regrind so closely approaches the regrind that gives the best metallurgical result that the difference between the two is insignificant in relation to the other uncertainties in regrind design. The main factor in regrinding design is the relation of the grade-recovery curve to fineness of regrind.
On this basis, the following approach to optimizing regrinding is a good option. The first and most important step is to obtain appropriate test data. The regrind tests must encompass a wide range from no regrind to about 20 µm K80. All samples must be subjected to similar treatment as far as possible, the only variable being regrind time. Each test must consist of three cleaning stages in order to improve a grade recovery curve. If the cyanidation is included in the circuit, the material first is reground and immediately leached. In this way, the metallurgist will have all the possible cases and will be able to take a logical and reasonable decision.
The results must be plotted on a grade-recovery curve. A secondary graph may be done by plotting recovery vs. regrind time for each sample. The optimum grind is represented by the maximum recovery point on the curves. If a different maximum is obtained for different concentrate grades, the maximum point that needs the finest regrind must be considered. For calculation of power requirements, the suggested procedure is to determine the work index at fine grinds and in refinement of these corrections for fine grinding power requirements. The traditional equipment installed in the regrinding circuit is a ball mill, with the time tower mills have been installed in several plants. The last equipment introduced in the market is the IsaMill, which is designed by performing power consumption tests.