Comminution involves crushing and grinding operations. The grinding operations use the traditional tumbling mills and stirred mills to reduce the ore to the required fineness. This thesis intends to investigate the influence of design and operating variables on the IsaMillTM specific energy and product size, when grinding UG2 platinum-bearing ore. The main objectives of this work were to study the effects of operating variables on specific energy consumption and product fineness, and to investigate IsaMillTM scale-up protocol. The experimental studies were conducted using the M4 IsaMillTM on a laboratory scale and the M10 000 IsaMillTM on an industrial scale. The laboratory scale M4 IsaMillTM was used to investigate the effects of some design and operating variables on the energy consumption and product fineness for UG2 PGM (Platinum Group Metals) bearing ore. There are many operating and design variables that have been shown to have a significant influence on the stirred mill operations (Clark et al., 2004; Jankovic, 2003; Pease et al., 2005; Zheng et al., 1996). This study, however, has focused only on variables that influence specific energy consumption and the product fineness of grind. The variables investigated include; stirrer speed, media load, media size, feed size, solids concentration and flow rate. Sampling campaigns were conducted on the M10 000 industrial scale IsaMillTM to evaluate the performance of large scale units. The campaigns were conducted at Anglo Platinum’s Waterval UG2 Concentrator and Western Limb Tailings Re-treatment Plant (WLTRP), which are both located in the Rustenburg area in South Africa. Waterval Concentrator treats UG2 platinum ore and has two IsaMillTM operating in mainstream grinding. The WLTRP, on the other hand, treats reclaimed material from the old Klipfontein tailings dam. The reclaimed material contains a mixture of UG2 and Merensky ore. The WLTRP has one IsaMillTM installed in fine-grinding applications to re-grind concentrates. While the results obtained from the test work have shown that when the IsaMillTM mill is operated at different speeds the energy required to grind UG2 ore of feed F80 = 120μm to a given product size (P80) varies. It was seen that lower speeds (1500 rpm) required more energy for given product size, increasing the speed to 1800 rpm resulted in a decrease in energy and further increase led to higher energy utilization. This indicates an existence of optimum speed when grinding UG2 ore of F80 = 120μm at 1800 rpm. In terms of the effect of media load, it was found that different media loads are required to efficiently grind various feed sizes (F80) of UG2 ore to desired product. Therefore, the IsaMillTM media load should be optimized at different levels for efficient grinding process. This study has indicated that the optimum media load is dependant on feed particle size. This test work also indicates that the performance of the IsaMillTM is greatly affected by the media size and feed particle size distribution. For the same stirrer speed, media load and slurry percent solids, it was found that the best grinding efficiency when grinding UG2 ore of feed sizes F80 = 55μm and F80 = 120μm were achieved when the 2mm media was used. However, the 3.5mm media was the most efficient media to grind the UG2 ore of F80 = 250μm. Therefore, the ratio of media to feed size must be matched and optimized in order to maximize the grinding efficiencies. Comparison of the data obtained from the sampling campaigns conducted on M10000 and the M4 IsaMillTM test work exhibited a consistent behaviour of industrial IsaMillTM that is closely matched by results achieved using the M4 mill. This suggests that the M4 laboratory scale IsaMillTM can be utilized to accurately estimate the energy required to prepare desired product fineness in M10000 industrial scale IsaMillTM. Therefore, the M4 can be used to generate data for design and operations optimization of industrial scale IsaMillTM.

show more