Experimental and numerical studies of selective fragmentation of mineral ores in electrical comminution Eric Wang, Fengnian Shi ⁎, Emmy Manlapig The University of Queensland, Sustainable Minerals Institute, Julius Kruttschnitt Mineral Research Centre, Qld 4068, Australia abstract article info Article history: Received 9 February 2012 Received in revised form 2 July 2012 Accepted 7 July 2012 Available online 16 July 2012 Keywords: High voltage pulse breakage Energy efficiency Selective fragmentation Numerical simulation An experiment was conducted in which two sulphide ores and one platinum ore were each subjected to high voltage pulses and mechanical breakage, with the same specific energy input, in order to compare the mineral modal abundance and grade in the two comminution products. The data from this experiment have provided unambiguous evidence of greater enrichment of the minerals with high conductivity/permittivity in the less than 0.3 mm size fractions of the electrical comminution product. Numerical simulations using COULOMB 3D indicated that with the existence of an electrical potential difference in the system, a high electrical field intensity was created around the boundary of the minerals with high conductivity/permittivity, causing selective fragmentation, thereby elucidating and supporting the experimental findings. © 2012 Elsevier B.V. All rights reserved. 1. Introduction World consumption of minerals is on the increase and this trend is likely to continue. However, the depletion of many high grade ore re- serves is leading to an increased need to process ores of lower grade. To liberate the valuable minerals from such ores requires fine grinding, a process which demands higher energy requirements and yields lower energy efficiencies. Addressing this comminution dilemma has become a major focus for the mineral industry. Consequently, improvements in rock breaking and mineral liberation techniques which can reduce energy consumption and improve metal production processing are being sought to address this challenge. The specific liberation process, such as the disintegration of ores by high voltage pulses, has been suggested as a possible route by which mineral liberation properties can be enhanced, relative to conventional breakage methods (Andres, 1977; Anon, 1986). In the technology of electrical disintegration, the process of liberation of minerals is determined by the locality of the split between different minerals along the boundaries. The ore fragments are immersed in a dielectric liquid (usually tap water) and experience high voltage pulse discharges, inducing the explosive breakdown of solids. The explosive breakdown is a result of plasma streamers occurring along the boundaries of minerals with different electrical conductivity and permittivity. Andres reported a number of comparative studies on the comminu- tion products of various mineral ores, including an apatite nepheline ore (Andres, 1977), diamonds that were liberated by high voltage pulses, without a single mechanical defect, that were cleanly detached from kimberlitic matrices (Andres, 1994), oxide ores containing hematite and PGM, and sulphide ores containing complex Cu sulphides and pentlandite (Andres et al., 2001a). All these results indicated that elec- trical pulses generated a higher percentage of liberated particles and a lower percentage of fine material than those obtained by mechanical comminution. Lastra et al. (2003) showed, in a comparative liberation study on a Merensky reef sample (comminuted by electrical pulse disaggregation and by conventional crushing) that the liberation of gangue was similar using either method, but the liberation of chromite, pentlandite, pyrrhotite and PGM was higher with electrical pulse disag- gregation than with a conventional jaw crusher. Ito et al. (2009) found that electrical disintegration resulted in preferential breakage of coal substances and mineral particles along their boundaries. High voltage pulse fragmentation is also used in geological applica- tion; with the advantage of allowing the liberation of minerals along the natural grain boundaries and existing deep fractures, without the unnecessary breakage of particles: a condition not achievable with con- ventional breakage methods. Chernet (2010) reported the use of high voltage pulses to release individual grains of gold, electrum and other minerals of interest, preserving their original texture, shape and size for detailed study of their morphology, surfacial features, grain size and composition. SelFrag (2008) showed an example of the selective fragmentation of a granite complete liberation and the recovery of mor- phological intact zircons and radiolarian chert. In recycling building materials, crushing concrete material with a multistage crusher or mill cannot separate the constituents, and the process also produces a large proportion of dust and small particles. However, high voltage pulses can break concrete along the boundary of the different constituents and recover sand, gravel and cement International Journal of Mineral Processing 112–113 (2012) 30–36 ⁎ Corresponding author. Tel.: +617 33655888; fax: +617 33655999. E-mail address: f.shi@uq.edu.au (F. Shi). 0301-7516/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.minpro.2012.07.005 Contents lists available at SciVerse ScienceDirect International Journal of Mineral Processing journal homepage: www.elsevier.com/locate/ijminpro