Selective breakage of mineralised particles by high voltage pulses

Abstract

Globally, the mining companies are struggling to achieve productivity improvements. This is partly attributed to the fact that the existing mechanical comminution methods disintegrate rocks in an unselective fashion whereby all the feed particles, including all the barren particles that are of no economic values, are comminuted to micro sizes to allow further beneficiation. The energy and resources devoted to the barren rocks are deemed wasted. This study explores the feasibility of applying the high voltage pulses (HVP) as a disruptive technology for selective treatment of the mineralised particles.Comprehensive test work with both real ores and synthetic particles has shown indisputable evidence of HVP propensity for particles that contain mineralisation. An improved multiple particles (MP) method has been developed. Different from the previous single particle (SP) method which forces HVP energy into every single particle, the MP method gives HVP complete “freedom” to differentiate particles by its own propensity so that the selective nature of HVP is utilized to a greater extent. The MP method is shown to result in better mineralisation deportment into the finer sizes, at a lower specific energy, than the SP method of HVP application. This enables higher metal recovery and waste rejection rates during ore pre-concentration.It is important when performing the laboratory HVP tests that the minimum quantity of ore sample required to achieve a statistically consistent HVP pre-concentration result is used. A method has been developed by firstly conducting multiple repeats of HVP tests with a small sample size. Then, numerical resampling of the experimental data was performed to produce virtual datasets of various larger quantities of ore sample. Statistical analysis on the virtual datasets was performed to establish the minimum quantities of ore sample requirement. To evaluate the sensitivity of HVP performance to the variation in sample size, a Sensitivity Index (SI) has been introduced and a mathematical description of the Sensitivity Index is presented.Synthetic particles made of grout embedded with various metalliferous minerals of different conductivities/permittivities were employed to provide further insights into the fundamental mechanisms that affect HVP breakage selectivity between particles. The effects of metalliferous grain locality in a particle, the feed particle position relevant to the electrode in the pulse treatment zone, and the interactions between various mineralised particles on HVP breakage selectivity and the energy transfer efficiency are demonstrated.In addition to the HVP selective breakage of particles, the synthetic particle study also found that HVP selectively weakens the mineralised particles using both micro (X-ray CT) and macro-scale (the JKRBT) examinations. The barren synthetic particles only exhibit minor damage in the internal structure and appear much more competent than the mineralised particles after HVP treatment. The results have suggested that barren rocks should be excluded in the downstream processes to maximise the HVP pre-weakening benefits. Using both particle surface scanning and X-ray CT internal tomography techniques, the study found that the HVP domain breakdown channel penetrated through the body of the embedded metalliferous mineral grain, rather than along its boundaries as reported in the literature, and completely disintegrated the whole mineral grains embedded in the synthetic particles.Two comprehensive case studies for two world major mining companies were conducted, which help identify the overall benefits of applying HVP for ore selective breakage in the mineral comminution circuit. The results have shown that Sample E is highly amenable to HVP pre-concentration and pre-weakening, whereas a marginal Cu pre-concentration performance and a modest pre-weakening effect was obtained with Sample F. The different response of the two ore samples to HVP treatment was reasoned from two ore-specific factors, namely material constitution heterogeneity and gangue mineralisation. Combining the findings from the synthetic particle study and the real ore case study, new understandings of HVP breakage selectivity and ore amenability to the HVP pre-treatment are generated.