Predicting the product particle size distribution from a vertical stirred mill

Abstract

The mineral processing industry has seen an increased use of vertical stirred mills, owing to the inefficiency of ball mills for fine grind applications. The difficulty encountered in fine grinding is the increased resistance to comminute small particles compared to coarse particles. As a result, increased energy inputs are necessary to raise the number of collisional events in a mill contributing to the comminution of fine particles. In this study, a research program was designed and implemented to predict the performance of a laboratory scale vertical stirred mill using a Bond ball mill. An energy-based population balance model was developed to analyze the response in product size resulting from changing operating conditions. The model prediction was compared with the results obtained in the laboratory vertical stirred mill. The grinding results show that changes in the feed size, stirring speed, and grinding media size are the primary parameters affecting the particle breakage rate. The test data also show that a finer product size is obtained when the mill operates at higher stirring speeds while using smaller grinding media. Samples collected from an industrial vertical mill were used to validate the model proposed in this study. Lastly, a numerical model was developed using Discrete Element Method (DEM) and calibrated in terms of power with the results obtained from the laboratory unit to quickly assess the effect of varying operating conditions on power draw.