Development of a simplified test for the determination of the Bond Ball Mill Work Index using a modified Hardgrove test

Abstract

Grinding ores in conventional ball mills demands high energy consumption, resulting in relatively high operating costs in a typical mineral processing industrial plant. Whether in the initial stages of a mining project or during its operation, conducting tests to determine the processing circuit’s energy consumption throughout the life of mine is necessary in order to reduce such high operating costs. Traditional tests used to determine the energy consumption in grinding, like the Bond Ball Mill test, are relatively time-consuming and require significant amounts of sample, e.g., 8–10 kg, which is not always available in the initial stages of a mineral project or geometallurgical studies. Several authors have developed simplified tests to predict ball mill’s energy consumption, typically using the Bond Ball Mill Work Index (BBMWI) as a reference. One option requiring less mass is the Hardgrove mill, traditionally used in the laboratory to determine the energy required to grind coal in roller mills. This test requires 50 g of sample, and the result is based on the amount of fines at the end of grinding to a fixed time. The present study used a modified Hardgrove test to predict the BBMWI. This test involves the measurement of the torque, uses a fixed sample volume with different particle feed sizes from the Hardgrove standard, and determines the specific energy related to the percentage of product passing through the closing size screen of the Bond test, defined as the size specific energy. The results indicated that for a set of 13 samples with the 150 µm closing screen, the average error associated with the predicted BBMWI is within ±2.3%. Further results indicate an error of ±3.1% for 20 samples with the 106 µm closing screen. The correlations presented here are proposed to be validated and/or adjusted for different ores and mines. The proposed test is thus suitable for geometallurgical studies and other applications where relatively small samples are available. In addition, this is a low-cost test, has a quick turn-around time, it is simple to conduct and does not require the handling of heavy loads by operators.