Process Optimization of a Small Scale BallMill for Mineral Processing using Discrete Element Method

Abstract

A ball mill is a grinding machine widely used in mineral processing to gradually decrease the size of ore particles. It is made of cylindrical drum supported by a frame. The inner partofagrindingmillcontainshorizontalbarknowsaslifterstoliftthecharge. Ballmills andcrusherareclassifiedamongcomminutionmachinesthatconsumethemostamountof energy in mineral processing industries. A lot of research has been conducted on various parameters that affect the power consumption of ball mill. It has been documented that the power consumption in ball mill usually depends on charge fill level, lifter geometry, and mill speed. In this work, a small scale batch ball mill was modeled and numerically simulated using a 3D DEM software (EDEM). Five types of lifter profiles; rectangular, trapezoidal, triangular, parabolic, and round, were investigated in terms of power consumption and impact load at mill speed ranging between 65-100% of the critical speed. DEM satisfactorily predicted power consumption and impact load for different lifter profiles at different percentages of critical speed. Lifter profiles were found to have average deviation in power consumption of 8.53 Watts as the lifter face angle changes from 0 to 25.56 degrees. This showed a significant impact on the power consumption due to the change in face angle. Lifter number as well as lifter height have shown marginal effect on the power consumption with the change in rotational speed. Rectangular lifters showed higherimpactloadandlowerpowerconsumptioncomparedtootherlifterprofiles. Sieving analysisdemonstratedthatmillspeedaffectthefinenessofthroughputand75%ofcritical speed resulted in the smallest particle size (11% of 150 µm particle passing through) at 209 Watts of power consumption. The lifter profile and its effect on power consumption and impact load finds application in the design and production of small scale ball mill to be used in different mineral processing firms. These include artisanal and small scale minersinMigori,Kakamega,andNarokcountiesinKenya,aswellasresearchinginstitutions. Theoptimizedgrindingprocessplaysagreatimpactinreductionofelectricitybills, as well as reduction of fuel consumption for small scale miners, hence requiring optimal lifter profile and effective grinding.