Electromagnetic sorting of metalliferous ores

• Main Author: John, Rebecca Shanti
• Published: University of Nottingham 2014
• Subjects: 622
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.716489

Around 4% of global electricity consumption is used for comminution in the mining industry. Falling head grades and increasingly complex fine grained ores mean that additional material must be processed to meet the rising demand for metal commodities. Ore sorting technologies have the potential to provide a step change in energy use by rejecting uneconomic material before it enters the comminution flowsheet. Microwave sorting of ores in combination with infra-red analysis of fragments has been shown in the literature to provide upgraded feedstock for certain ores at bench scale. In this thesis, Pilot scale microwave sorting tests of porphyry copper ores indicated that deviation from intrinsic sortability is due to the presence of microwave susceptible hydrated clay minerals within the gangue, with approximately twice the mass of copper sulphides to clay minerals required to achieve equivalent temperature rise. Pilot scale radio frequency sorting tests were undertaken using a novel methodology to mitigate shape effects. They revealed significantly enhanced correlations between fragment temperature rise and clay mineral content, particularly for the higher moisture content ores. The effects of ore fragment texture on IR thermal profiles were investigated using experimentally validated numerical modelling. Whilst different fragment textures lead to the development of significantly different thermal profiles, increasing the measurement delay time between electromagnetic heating and surface thermal profiling reduces the difference between fragments of the same grade but with different textures. Testing of synthetic fragments containing varying grades of pyrite and clay indicated that semiconducting minerals cannot be heated successfully in pure electric fields. Induction heating trials showed that semi-conducting and magnetic minerals heat well in magnetic fields compared to rock forming minerals. Induction heating potential measurements showed that samples from different geological sources have different magnetic heating behaviour; coarser grains were shown to heat better than finer grains.