Use of high voltage pulse technology to investigate the mechanism of mineral breakage and selective liberation

Wang, Hao-liang (Eric) (2012). Use of high voltage pulse technology to investigate the mechanism of mineral breakage and selective liberation PhD Thesis, Sustainable Minerals Institute, The University of Queensland.

       
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Author Wang, Hao-liang (Eric)
Thesis Title Use of high voltage pulse technology to investigate the mechanism of mineral breakage and selective liberation
School, Centre or Institute Sustainable Minerals Institute
Institution The University of Queensland
Publication date 2012
Thesis type PhD Thesis
Supervisor Frank Shi
Emmy Manlapig
Total pages 214
Total colour pages 55
Total black and white pages 159
Language eng
Subjects 091404 Mineral Processing/Beneficiation
Formatted abstract The application of high voltage pulse technology in mineral processing is fairly recent and brings potential as alternative comminution equipment. A review is given of the literature relating to the theory and applications of high voltage pulses in many industrial areas.

A novel comminution method has been reviewed and investigated by applying high voltage pulses at specific energy 1-3 kWh/t to pre-weaken mineral particles, leading to reduction in energy consumption in the downstream grinding process. Four ore samples were tested using high voltage pulses and conventional crushing in parallel for comparison. Evidence of cracks and microcracks measured with X-ray tomography and mercury porosimetry supported the principle of high voltage pulses induced damage on rocks in the electro-comminution process, which resulted in energy saving up to 24% found in this study. Ore surface texture and mineral properties affected the efficiency of high voltage pulse breakage.

Comparative comminution between high voltage pulses and conventional grinding, at the same specific energy levels, shows that electrical comminution generates a coarser product with significantly less fines than the mechanical breakage. However, minerals of interest in the electrical comminution product are better liberated than in the conventional comminution with over 95% statistical significance. There is a potential to use less energy in the electrical comminution. Distribution of the liberated minerals appear in size fractions coarser than 53µm; while in the mechanical comminution product, the liberated minerals are accumulated in the fine and very fine size fractions. Therefore there may be potential benefits in recovering the coarse liberated minerals in the electrical comminution product, prior to further grinding.

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 has 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.

Factors affecting electrical comminution performance were investigated through experimental work and numerical simulations. The effects of feed size, under-sieve classification, incremental breakage and energy input level on particle pre-weakening and mineral liberation were tested with six ore samples. Using commercial software, COULOMB 3D, simulation was used to explore the trends between the electrical field distribution/intensity, and the ore particle electrical/mechanical properties. These results were used to interpret the differences in breakage and liberation for various ores. The results showed that the induced electrical field is strongly dependent on the electrical properties of minerals, the grain size, the location of the conductive minerals in rocks, and the particle shape.

Apparently, ore texture, particle mineralogy and other electrical/mechanical properties all affect the efficiency of high voltage pulse breakage. It is emphasized that the feasibility of electrocomminution and the benefits can be achieved need to be investigated case by case.
Keyword Comminution
High voltage pulse breakage
Energy efficiency
Mineral liberation
Pre-weakening

 
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Created: Fri, 19 Oct 2012, 09:56:42 EST by Hao-liang Wang on behalf of Scholarly Publishing and Digitisation Service