Liquid Mining: Olympic Dam in a Test Tube

16 January 2013

New minerals research at the South Australian Museum is set to change the face of the mining industry.

South Australian Museum Head of Earth Sciences Professor Allan Pring and his team are working on the concept of 'liquid mining'. "Imagine being able to get copper out of an ore body without having to dig any holes – that's the holy grail that we are working towards," says Professor Pring.

The disturbance mining can cause to the natural environment is one of the most controversial aspects of the industry. The South Australian Museum team is working on a method to inject liquid into underground ore deposits and dissolve the minerals out of the ground, meaning very little natural disturbance at all. They are studying the precise chemical and physical conditions that help form valuable ore deposits, like those at South Australia's Olympic Dam, 560 km north of Adelaide.

Around 180,000 tonnes of copper are produced from Olympic Dam each year, a number that could triple if the mine is expanded. "The processes that form huge ore bodies like Olympic Dam, which is approximately 6km long and 3km wide, actually operate at the atomic or molecular scale," says Professor Pring.

That's why scientists at the South Australian Museum are also able to make copper in our laboratories. While the amount is much smaller, it has enormous potential. Usually, minerals are made in labs by combining solid materials under high temperature and sometimes, under high pressure. However, the South Australian Museum team's approach is much more unique – it's working to make minerals from water-based solutions.

"If we can form a mineral from an aqueous solution, then we will know the conditions needed for a mineral to become stable. We can then work out the reverse process needed to make the mineral unstable, and move," says Professor Pring says.

This potential breakthrough would help mining companies extract the prized minerals from the ground. Specially-designed liquids could be injected into an ore deposit and then target a particular mineral, dissolving it out of the ore. The liquid could then be pumped to the surface where the metal could be easily collected.

'Liquid mining' is not as far-fetched as you might think. Professor Pring says perfecting the chemical solution will take place in the next decade. Additionally, the mining industry is not the only sector to benefit from Professor Pring's research: it could also improve efficiency in the geothermal and oil industries.

"If we can work out the right solution that will dissolve certain minerals, then we will effectively be able to open and close rocks," Professor Pring says.

The South Australian Department for Manufacturing, Innovation, Trade, Resources and Energy (DMITRE) recognises the exciting possibilities of this research. Deputy Chief Executive of Resources and Energy at DMITRE, Dr Paul Heithersay said improving the understanding of how economic minerals are formed, could lead to benefits locally and abroad. "A fundamental understanding of the formation of ore minerals allows new exploration techniques to be devised and new technologies for ore liberation to be developed," Mr Heithersay says.

Specifically, the South Australian Museum team is working to create copper and gold ores and the associated iron sulphides. The researchers need to be resilient – it can take hundreds of experiments before they find the right combination of temperature, pressure, time and chemical solutions to create the mineral. The temperatures used range from 200–500°C and the pressures needed are extraordinary – from 30 to 1000 bar. The highest pressures used are equivalent to around 400 times the pressure in a car tyre, or about 160 times the pressure inside a champagne bottle.

Fortunately, once the right combination has been discovered, the minerals can be made quite quickly. Copper and iron sulphides are now made at the South Australian Museum within just a week. While only less than a gram of copper is made by each reaction, the implications are far-reaching for the copper mining industry.

"When you're mining ore that contains copper at low concentrations – a fraction of a per cent – then you have to move an awful amount of rock to get the copper out. You end up with huge piles of waste rock that are ground to a fine powder. Not having to use the energy to do all of that would improve mining enormously," said Prof Pring.

Once the right conditions for mineral formation have been identified in the laboratory, then this can be used with knowledge of local geology to better predict the distribution and grade of ores within the landscape. This will lead to better exploration outcomes as well as increasing the efficiency of mining, ore treatment and waste rock management.

There are also enormous potential results for the geothermal industry. Geothermal systems use hot rocks in the earth to heat water and the heat is harnessed to create energy/electricity. Water is pumped through minute cracks in the rocks and often travels at high pressure, moving at around 70 litres per second.

The ability to open and close rocks using liquid solutions would help to increase the capacity and efficiency of geothermal energy systems. Channels within the rock could be created by using specific liquids to dissolve portions of the rock and improve water and heat transfer within the rocks. Similarly, a liquid could be designed to absorb both heat and specific metals from the rocks, effectively mining and creating energy at the same time.

"If you know under what conditions the mineral will dissolve, and you know the rock type, you can create channels in the rock. These are just big enough for water to flow through, in the case of geothermal energy, or for fluids to come out as in oil extraction," Professor Pring says.

If rocks could be 'opened' or cracked, then oil extraction rates could also be improved. At the moment only about 50% of the oil in reservoirs can be extracted. The remaining oil is often trapped within small pores in rocks and cannot be pumped out. If the pores within the rock could be broken open by a tailor-made liquid, then the remaining oil would be released for extraction.

"It's like a giant jigsaw puzzle. We're working in one area and we can see how our work will impact on many other areas," Professor Pring says.

His research is supported by the outstanding mineral collection at the South Australian Museum. The South Australia Museum's Mineral Sciences Collection is currently valued at $13–$14 million and houses more than 35,000 specimens. Haematite and magnetite from the collection, originally from the Iron Monarch mine in South Australia, is dissolved into solution for the experiments. At least a kilogram of solid material is needed and if this can't be sourced from within the current collection then additional pieces are acquired. It is important that all of the material used comes from the same piece of rock to help standardise the experiments.

With copper production worth more than $6 billion a year and crude oil production worth around $8.7 billion a year in Australia alone, the small scale mineral production at the South Australian Museum has Olympic Dam-sized implications.