Ore particle breakage behaviour in a pilot scale high voltage pulse machine

Highlights

• Three ores were tested with a pilot scale high voltage pulse machine.

• Various operational conditions on ore breakage behaviour are investigated.

• Ore properties affect high voltage pulse breakage performance significantly.

• The laboratory and pilot scale machines treating the same ores were compared.

• Optimising ore breakage performance through processing zone design was suggested.

Abstract

SELFRAG AG has developed a flexible pilot scale Pre-Weakening Testing Station (PWTS) using high voltage pulses (HVP). This provides a unique opportunity to investigate the machine setting conditions on ore breakage behaviour. A joint campaign was undertaken by the Julius Kruttschnitt Mineral Research Centre and SELFRAG AG to investigate the breakage behaviour of two copper–gold ores and one iron ore in the PWTS. The effects of specific energy, pulse voltage, cumulative discharges, feed particle size and ore particle breakage pattern (body breakage or surface breakage) were investigated. The investigation revealed that the mass-specific energy of HVP was the most significant factor affecting the breakage behaviour in the PWTS. This effect was compounded with the effects of ore properties and particle size. Comparison between the PWTS and a laboratory HVP machine indicates that there is considerable scope for optimisation of HVP performance based on processing zone design.

Introduction

Comminution remains by far the largest energy consumer in the mining industry. The high energy consumption implies both a high operational cost and a greenhouse footprint. As one of the potential technical means of reducing the energy consumption of comminution, pre-weakening of ore particles by high voltage pulse (HVP) has attracted the attention of researchers in the past few years (Usov and Tsukerman, 2006, Wang et al., 2011, van der Wielen et al., 2013, Razavian et al., 2014).

HVP breakage is a comminution method that uses high voltage pulses to initiate electrical breakdown inside ore particles that are immersed in water, generating a strong tensile force to disintegrate the particles. The research found that particle strength of a number of ores can be reduced significantly by HVP treatment using a low specific energy (Wang et al., 2011), thus reducing the energy consumption in the downstream comminution process. A number of potential applications of HVP technology in the mineral industry have been proposed, including pre-weakening the AG/SAG feed, hard particles treatment, ball mill feed pre-treatment, etc. (Shi et al., 2012). In addition, Shi et al. (2014a) demonstrated that, taking into account both HVP and mechanical breakage energy consumptions in a hybrid circuit simulation, the pre-weakening effect on energy reduction through changes in comminution circuit configurations is significant.

The initial study of pre-weakening by HVP breakage was performed with a selFrag Lab device manufactured by SELFRAG AG based in Switzerland (Wang et al., 2011). The selFrag Lab is primarily designed for the selective fragmentation of composite materials, mineralogical and geological samples in the kilogram range, rather than for pre-weakening study purposes. In order to demonstrate the benefits of HVP pre-weakening to the mineral industry, the equipment has to be scaled up to treat larger particles with more flexibility in operation settings. SELFRAG AG has recognised the need and developed a pilot scale Pre-Weakening Test Station (PWTS), which is a purpose-built R&D machine at the SELFRAG pilot plant (van der Wielen et al., 2014). In comparison with the selFrag Lab, the advantage of the PWTS is that it offers more flexibility in terms of generator setup, as well as the possibility to process continuously. Voltage and capacitance of pulse generator can be adjusted independently for the PWTS, allowing testing of same pulse energy but different voltages. Investigation of the ore particle breakage behaviour in the PWTS is helpful in further development of the HVP technology.

van der Wielen et al. (2014) conducted a detailed HVP breakage characterisation on a sample of granite with the PWTS. It was found that the relation of pre-weakening degree of the granite sample to specific energy is similar to the impact breakage product fineness-specific energy relationship described by JKMRC breakage model (Napier-Munn et al., 1996). The work helped to understand rock breakage behaviour in HVP breakage, but may not well represent ore breakage behaviour. The difference in breakage behaviour under HVP treatment between rocks and ores can be exemplified in a recent study that the content and location of the minerals with high permittivity/conductivity affect breakage behaviour of ore particles (Zuo et al., 2014, Zuo et al., 2015a). In order to obtain a thorough understanding of ore particle breakage behaviour in the PWTS, a joint campaign was conducted by the Julius Kruttschnitt Mineral Research Centre (JKMRC) and the PWTS manufacturer SELFRAG AG. This study investigated the breakage behaviour of three ore samples, two copper–gold ores and one iron ore, in the PWTS under different operating conditions. The major findings of ore particle breakage behaviour in the PWTS are presented in this paper.