Determination of the milling parameters of a platinum group minerals ore to optimize product size distribution for flotation purposes

Most concentrators desire to operate under optimal design configuration that guarantees high mineral recovery and low operational costs. The optimal design configurations are determined through studying the material to be milled in a laboratory mill under standard conditions. This is achieved through determining the selection and breakage function parameters and applying the mathematical simulation of the grinding process in order to optimize the size reduction process. The desired particle size is determined by the downstream processes, in our case, flotation. To this end, three mono-size classes feeds 850–600 μm, 600–425 μm and 425–300 μm of a platinum ore were ground using three different ball sizes (10, 20 and 30 mm) in a laboratory mill for the grinding times 0.5, 1, 2, 4, 8, 15 and 30 min. The data collected was used to determine breakage and some of the selection function parameters. The remaining parameters were back-calculated within the population balance model framework. The parameters were then used to obtain the product size distribution (PSD) that was later compared with the experimentally measured one. The milling kinetics for the desired size class for flotation was also simulated.There was a good match between the predicted and the experimentally measured PSD. The results of the milling done for further 60, 90, 120 and 240 min to validate the simulated milling kinetics from the determined parameters also showed good match between the simulated and the experimental one. This further confirms the validity of the determined parameters. From this, it becomes possible to determine the grinding conditions for optimal flotation.

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► Milling parameters of the PGM ore are measured and others back-calculated.
► Simulated and measured product size distributions were satisfactorily compared.
► Milling kinetics of the desired size class for flotation were simulated using the parameters.
► Results show good match between experimental and predicted.
► Validity of the determined parameters was confirmed through further batch grinding.