UBC Theses and Dissertations

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UBC Theses and Dissertations

Scale-up and operations of a vertical stirred mill Francis, Baker


Stirred media mills are relatively new to mining industry, and several new technologies have been developed such as the VXPmill (vertical stirred mill). There is little technical understanding of optimizing and scaling-up of the VXPmill. This thesis addresses both of these issues and therefore supports commercial applications of this vertical stirred mill. Stirred media mills are influenced by a great number of operating variables. A study was conducted to understand the influence of mill speed, feed particle size and, slurry density and rheology on the VXPmill performance. For scale-up, a study was conducted to compare the batch recycle and the pendulum testing procedures. A scale-up demonstration study was also done utilizing the pilot-scale (VXP10) mill and the full-scale (VXP2500) mill to validate the procedure. The following are the main findings from this work: There is an optimum tip speed such that if too high (12 m/s) results in energy losses due to mechanical friction and heat. If too low (3 m/s) there are insufficient stresses to promote breakage. The optimum tip speed was found to be about 7 m/s. Feed particle size is an important variable when predicting the energy-size reduction relationship. A coarser feed requires more energy than a finer feed to achieve the same grind size. The batch recycle testing procedure overestimates the energy consumption as compared to the pendulum test over a broad range of grind sizes. Therefore, it should not be used for scale up applications. However, the pendulum test can be used to predict energy requirements for scale-up. By utilizing the VXP10 mill, the stress intensity of grinding beads and specific energy input control the grind size for the comminution of feldspars-quartz ore. At optimum stress intensity, the energy utilization is maximum. For the effective and accurate scaling-up of stirred media mills, it is extremely important that both the pilot-scale and the full-scale mills are operated at relatively similar operating conditions, and treating similar material of the same feed particle size. However, both mills should be operated at their optimal flow rates.

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