With demand for minerals increasing while Australian ore grades decrease, a new method for processing higher quantities of ore needs to be developed to maintain current metal production rates. 

Traditionally, mineral processing plants use a process called ‘comminution’ to crush and grind ore into fine particles to separate and extract the different mineral components.

This process uses 158 trillion kilojoules of energy every year for just Australian copper and gold – 16 times the energy consumption of a city like Brisbane.

The mining industry now faces a serious question.

How will we produce the metals society needs in a way that is economically and environmentally sustainable for the future?

The team approach this challenge with what Professor Shi calls a ‘disruptive technology’ for the industry – high voltage pulse.

High voltage pulse (HVP) technology has been left on the backbench for decades.

“In the 1950s Russians attempted to decompose water into hydrogen and oxygen and in the 1970s it was finally used in a mining context to liberate valuable minerals from ore, at a high energy cost,” said Professor Shi.

 

Many years later, the SMI-JKMRC HVP comminution team approached this research topic from a new angle. 

Instead of using HVP as a comminution tool, they use low HVP energy to selectively break the ore and change ore processability, allowing for better performance of downstream processes and savings in energy. 

Professor Frank Shi standing with SMI-JKMRC’s SELFRAG HVP Unit.
The X-ray computed tomography (XCT) image shows a chalcopyrite mineral grain (in yellow) induced HVP breakdown channels (in blue) in a synthetic rock (in grey), scale in mm. 

“We found that the high voltage pulse can find whether a particle contains valuable minerals or not,” said Professor Shi.

“Similar to how a golf club will attract lightning in a storm, high voltage pulse has a selective breakage mechanism where the ore containing high conductivity/permittivity minerals is broken while the barren rock is not.

“We can use this new technique to reject the waste at an early stage and save energy to make the mining industry more sustainable.”

In the lab, they submerged two small synthetic rocks into the water of the HVP processing vessel – one barren and one containing chalcopyrite.

Operating parameters such as electrical voltage, current, capacitance, resistance, inductance, pulse frequency, and electrode configurations were controlled to optimise the system.

When the machine started, a bang is heard as 180 kilovolts were discharged into the rocks for one pulse.

One rock remained intact, but the other was fragmented and could easily be further broken by hand.

This meant the broken rock contained valuable mineral, and shiny metal could clearly be seen on the newly exposed surface.

Fragments could fall through the holes in a screen, while the barren rock could not, allowing it to be screened out.

This is the discovery that was further developed into a novel ore grading splitting and preconcentration technique, that selectively breaks mineralised particles with high conductivity/permittivity, while leaving the barren rock whole.

In the mining industry, this barren rock is commercially valueless material called gangue. In the case of processing base and precious metals, more than 95% of the run of mine feed consists of gangue minerals without industrial value. In one instance using a particular ore, it is possible to use HVP treatment to reject 45% of the run of mine feed by simple screening and still recover 80% of the gold.

Professor Shi estimates for a 20 million tonne per annum operation, rejecting 30% of barren rocks would result in a $14 million per annum saving in haulage costs, and also bring significant benefits with respect to water use and tailing treatment.

The project also intends to reduce grinding energy consumption, which is the heart of mineral and metal extraction.

“Grinding is the single largest energy consuming process in any mineral processing plant, which is a constraint in the processing of low grade ores, and a significant barrier in the near future when even lower grade ores are treated,” Professor Shi said.

 

Ultimately, high voltage pulse will increase mining operation profitability.

The value of this research was recognised when a paper on the topic, authored by Frank Shi, Weiran Zuo and Emmy Manlapig, won the prestigious 2017 Coalition for Energy Efficient Comminution (CEEC) Research Category Medal.

“I hope it will help us to source the funding required to enable us to continue work with HVP in 2018 and onward.

“It’s just good timing, because we are currently seeking to take our research outcome from the laboratory to a larger scale, and we need the mining industry to support and fund this campaign.”

In 2018, the team will initiate a new collaborative research project focused on bridging the gap between lab-scale research and industrial-level operation and has submitted patents for innovative equipment developed to achieve this goal. Newcrest and UQ are co-funding a new flexible HVP testing facility at SMI-JKMRC to house this equipment which is scheduled for commissioning mid-2018.

Experts from various disciplines are being brought together for this project, including Dr Kym Runge, Professor Rick Valenta, Dr Christian Antonio, Dr David Seaman, Professor Emmanuel Manlapig, and collaborators from a University in China.

This project owes its success to its many investors who saw its potential – the Sustainable Minerals Institute, Australian Research Council (ARC Linkage-AMSRI and ARC LIEF projects), University of Queensland, The University of South Australia, University of Newcastle, University of Melbourne, Australian Postgraduate Award Industry, Newcrest Mining, Anglo American Centre for Sustainable Comminution, China Scholarship Council, SELFRAG AG, as well as a number of other mining companies in supporting HVP characterisation of their ore samples.

 
 
 

This project owes its success to its many investors who saw its potential – the Sustainable Minerals Institute, Australian Research Council (ARC Linkage-AMSRI and ARC LIEF projects), University of Queensland, The University of South Australia, University of Newcastle, University of Melbourne, Australian Postgraduate Award Industry, Newcrest Mining, Anglo American Centre for Sustainable Comminution, China Scholarship Council, SELFRAG AG, as well as a number of other mining companies in supporting HVP characterisation of their ore samples.

Contact details:
Professor Fengnian (Frank) Shi
The Julius Kruttschnitt Mineral Research Centre (SMI-JKMRC)
T: +61 7 3365 5913
E: f.shi@uq.edu.au