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Comminution

The Comminution Group was formed in 1997 as a new research thrust and now accounts for more than a quarter of the research outputs for the Centre for Minerals Research. The group has nine staff members and more than 14 post graduate students and has become one of the leading centres of comminution research in the world.

Our aim is to attract a cross-section of students and academics to develop the fundamental understanding of unit processes in comminution, and for applied engineers to work closely with plant personnel to conduct on-site tests on production plants. The information from fundamental and on-site experiments is then used in models which are in turn used on production plants for design and optimisation. As a background to this research all students are given training in minerals processing, and do at least one set of site test work. We are also developing ever-closer collaboration with the Flotation section, so as to provide an integrated research thrust. In this way we hope to produce graduates who are useful to industry and have contributed to the overall understanding of minerals processing.    

Comminution
The study of rock breakage has drawn in fundamental mathematical modelling, computational modelling, physics students using medical x-ray equipment, physics and engineering students using nuclear physics techniques such as the Positron Emission Particle Tracking (PEPT) system to perform experiments for validating comminution equipment models, and applied work on operating plants to collect the real data and learn our science.

Ore breakage characteristics studies with the aim of improving the efficiency of comminution devices are performed using Split Hopkinson Pressure Bars (SPHB) and Ultra Fast Load Cells (UFLC). This crossover of applied and fundamental sets us up as leaders in moving the science a major step forward over the next few years.

The overall objective of the group is to improve the efficiency of comminution circuits, while training students in skills useful to the mining industry.

Comminution circuits present some major challenges. Mills are energy intensive and expensive to operate, and have low rated energy efficiency relative to simple particle breakage. Understanding and modelling the comminution process for each piece of equipment within a circuit is the key to optimising current operations and improving the design of new comminution circuits.

Design of mill linings and pulp lifters have been shown to influence the milling action. This, linked with the high cost of wear components, motivates continued study of design and construction materials.

Classification
Classification of the product is the other most crucial step in comminution. The main purpose of comminution is to liberate the minerals so that they can be recovered in the subsequent process stages. The correct particle size range and distribution must be produced to optimise the extraction process, which is the end objective of the whole mining operation. The classification stage is usually installed in the comminution circuit to ensure that only the correct size range or distribution reports to the subsequent process stage. A number of mining applications have specific problems with uneven classification of different density materials. This results in over-grinding of one mineral as it repeatedly reports to the cyclone underflow and subsequently overloads the circuit with a high re-circulating load. This reduces milling capacity and produces an undesirable size distribution of the final product. The group is involved in developing models for hydrocyclones, testing of special types of classifiers such as the three-product cyclone, and assessing circuit configurations involving fine screens.    

To make a meaningful contribution to improving this efficiency, it is necessary to understand how the grinding and classification takes place, and what can influence it. Fundamental studies of charge motion and flow patterns in classifiers and realistic mathematical models derived from these studies provide the key to addressing these problems. Fundamental understanding can then be put into practice through plant and pilot trials, where real-life factors can be incorporated into the mathematically correct frameworks. The potential rewards are great in terms of reliability of design, cost reduction, higher throughput, and controlling the product.