Comminution is a process of reducing the size of ore particles to liberate the minerals in preparation for extraction in downstream processes, and classification is installed to ensure that liberated minerals enter the recovery section of the process plant and those not ready are recycled. The overall objective of the research performed in the area of comminution and classification is to gather empirical data for the development of heuristics and mathematical models that can be used for optimizing and designing industrial grinding circuits. The research performed in this area is divided into two broad themes: the comminution theme covers all studies concerned with size reduction of ore particles and the classification theme focusses on the selection of correctly sized particles for further processing downstream. Extensive research is conducted to understand the individual unit operations involved in the two broad themes at industrial, laboratory and pilot-plant scale. In addition, an appreciable amount of computational research is conducted to provide insights on the mechanisms underpinning the unit operations that are studied.

Research Themes

Comminution: Comminution utilises energy to reduce the size of ore particles in order to liberate embedded mineral grains so that they can be recovered in the subsequent process stages. The research under this theme focusses on understanding how energy is used in devices that use different breakage mechanisms to achieve size reduction and how energy is utilised in different comminution circuit configurations. The knowledge generated from these studies is used to develop heuristics and models that can be applied to unit operations or entire comminution circuits to improve energy efficiency without compromising downstream processes. The equipment studied include tumbling mills, stirred media mills, high pressure grinding rolls and vertical roller mills. Ore breakage characterisation is performed as part of comminution research to assess the response of various ore types when subjected to different breakage mechanisms. Computational and particle tracking studies assist in the investigation of the underlying mechanisms that characterise the function of both novel and current comminution technologies.

Classification: Research in the area of classification focusses on improving the efficiency of particle separation in different classifiers. Since classification is based on the size, shape, and density of particles, the research in this area is focussed on identifying the best classification system for the material produced by comminution devices based on the three properties as well as downstream requirements. Computational and particle tracking tools are also used to study underlying separation mechanisms that govern the operation of different classification devices.

Activities Supporting Research Themes

Industrial Site Sampling Campaigns: The research on comminution is focussed on reducing energy consumption. Data is collected using industrial site surveys, pilot and laboratory scale studies. Industrial campaigns are the preferred method of collecting data from operating comminution equipment. Therefore, most of the work under comminution research is conducted on sponsor sites, and the data collected is used to optimise the performance of those mills.

Pilot-scale Site Sampling Campaigns: Due to the difficulties encountered in collecting all relevant data from industrial surveys a significant amount of work is done at pilot plant scale. Pilot plant scale is important because the charge from equipment such as tumbling mills can be emptied out to study the charge characteristics from tests performed at different operating conditions. Ore breakage characterisation studies are performed using Split Hopkinson Pressure Bars (SPHB), Ultra Fast Load Cells (UFLC) and the Julius Kruttschnitt Rotary Breakage Tester (JKRBT).

Computational Methods: Computational tools such as discrete element methods (DEM), Computational Fluid Dynamics (CFD) and Smooth Particle Hydrodynamics (SPH) are employed to study the mechanisms under pinning the motion of the charge in comminution devices. However, the computational models require validation to ensure that the data generated using these methods is reliable. Laboratory experiments are performed to generated validation data sets for computational models. Nuclear physics techniques such as positron emission particle tracking (PEPT) are used to obtain the validation data sets.