Metal Tech News - The Elements of Innovation Discovered

A team of international researchers have developed a new mining technique that will advance humans beyond the Bronze Age when it comes to extracting copper, gold, silver, and other conductive metals out of buried bodies of ore.

Since humans began using metals on an industrial scale some 5,500 years ago, we have depended on physically digging up the metal-bearing rocks from underground tunnels or quarries, crushing the ore, and then using various techniques such as heat or chemicals to extract the metals.

The international research team has developed a proof of concept for the application of a non-invasive mining technique that involves using an electric field to control the movement of an acid within a low permeability copper-bearing ore deposit to selectively dissolve and recover the metal while it is in the ground and then pumping the metal to the surface.

The researchers believe this technique has the potential to transform the mining industry at a time when the world will be needing massive amount of copper and other metals for the transition to non-carbon energy sources and electric transportation.

Not needing to dig out rocks that contain no metals at all to get to other rocks that must also be dug out and crushed to extract the metals, the technique would make the mining of green energy metals such as copper more sustainable and economical.

"This new approach, analogous to 'key-hole surgery,' has the potential to provide a more sustainable future for the mining industry, by enabling the recovery of metals, such as copper, which are urgently needed for our global transition to a new green economy, whilst avoiding unwanted environmental disturbance and energy consumption," said Rich Crane, senior lecturer in sustainable mining at the Camborne School of Mines, University of Exeter.

Crane is among a team of 10 researchers that recently published a report on the newly developed technique, "Toward a more sustainable mining future with electrokinetic in situ leaching," in Science Advances.

While in situ mining of uranium has been around for roughly six decades and has begun to make its way into mining metals such as copper, gold, and silver, electrokinetic in situ leaching adds a new element that makes the technique for conductive elements more efficient – an electrical current.

In their publication, experts from the University of Western Australia, the Commonwealth Scientific and Industrial Research Organisation, the Technical University of Denmark, and the University of Exeter, have demonstrated that a targeted electric field can be used to dissolve and then recover copper and other metals directly from the ore.

This technique works best when the orebody is saturated with water, which happens to be a situation that makes traditional mining more difficult due to the management, storage, and treatment of the water so that the mine does not flood.

University of Exeter

The figure on the right shows an industrial-scale electrokinetic in situ leaching operation, including potential electrode configuration, renewable energy source, lixiviant (fluid to dissolve the metals) supply and recovery reservoirs, and metal recovery treatment facility. The center figure illustrates the ore interface between an individual anode and cathode. And the figure on the right illustrates the principal hydrogeochemical reactions between the lixiviant and the ore material when subjected to electrokinetic-driven electromigration.

This team says the technique they have developed would be ideal for deep porphyry deposits such as the Pebble East giant copper-gold deposit in Alaska and the deeper ore zones at the Escondida porphyry copper deposit in Chile.

The technique for extracting the metals from deposits such as these would involve drilling holes down to insert positive electrodes (anodes) and negative electrodes (cathodes) and then injecting an electrolyte material that dissolves the metals. An electric current would cause the metals ions to move through the rocks toward the electrodes via a process called electromigration.

While this technique has focused on copper and the scientists have already demonstrated it works on gold, this technique should also work on "a wide range of minerals containing silver, zinc, cadmium, lead, manganese, lithium, molybdenum, selenium, vanadium, scandium, yttrium, rare earth elements, indium, beryllium, chromium, gallium, nickel, and cobalt."

The research team has now provided a proof of concept for this new electrokinetic in situ leaching technology at laboratory scale and has verified it with computer modeling. They are confident that the idea can easily be scaled up to the commercial un-mining required to deliver copper and other metals to the green energy and transportation revolution.