Metals Recovery Using Ionic Liquids

Argo Applied Technology is looking at Deep Eutectic Salt technology to change radically the way metals could be processed in the future. Daniel Major explains this exciting new recovery method.

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Daniel Major, the head of applied technology at London-based Argo Applied Technology, first presented the DES technology at Mines and Technology Toronto in October 2018. We caught up with him to hear his views on the latest mineral-processing technology.

Delegates at Mines and Technology (M&T) in Toronto were interested to hear about Deep Eutectic Salt (DES) technology. Can you explain what is causing the excitement?

DES has the potential to change radically the way metals could be processed in the future, being able to dissolve metals to higher purity than water-based systems, and so reducing refining and smelting requirements.

The technology is a non-toxic, non-caustic subset of Ionic liquids, which are salts that are liquid at low temperatures. These anhydrous liquids are composed of ions and, like high temperature molten salts, are electrolytes and powerful solvents. In contrast to aqueous liquids, where the solubility of metals is limited by the tendency for water to combine with metal ions and precipitate oxides and hydroxides, much higher metal concentrations can be achieved in water-free ionic liquids.

How do these unique features help metals recovery?

The features of Ionic liquids provide potential for high selectivity in both metals dissolution and recovery. These liquids have a wider electrochemical window than aqueous solutions, and so can operate beyond the potential range of aqueous solutions. This makes electro-winning of more reactive metals possible, whilst avoiding the evolution of gas at the electrodes.

How long has this technology been under development?

DES has been under development for over 20 years, and is moving towards commercialisation in a number of industries. This includes the electro-deposition of chromium, extraction of natural products in cosmetics, metal fluxes and electropolishing, but is only now being directed towards mining and the processing of ores. Based on the experience of Argo's technical team, there are some areas where we can see benefits and potential growth for DES, and these are the initial targets as we continue to develop DES.

Can you be more specific about these targets?

The technology is non-toxic and based bio-degradable salts, such as choline chloride and urea. In the gold industry, for example, this will replace the use of cyanide and mercury in processing ore to create refined gold.

The process also enables dry processing, producing water-free solvents that can be recycled, and so reducing water consumption as well as waste in processing. The inputs to the DES process are cheap — being available in industrial quantities and globally.

The high selectivity will improve recovery rates. In the case of gold, recoveries are 80x faster than with cyanide (at 25°C). There is also the potential to recover more products economically.

So is the process fully proven?

DES has already been proven to dissolve a large number of industry standard minerals — including Au, Ag, Pt, Pd, Ni, Cu, Mn and Cr. Refractory minerals can also be dissolved, for example pyrite and chalcopyrite.

What is the next stage?

There may be potential to build a single plant for oxide and sulphide gold ore. In addition, once in solution, different techniques can be used to extract individual metals. Hence, we are looking at the potential of dissolving the metals from complex ores, such as PGMs, and be able to extract the metals and avoid the complex smelting and refining process currently employed.

There is the potential ability to improve in-country beneficiation of ores to near final product.

So an exciting development? 

Absolutely. As the late Professor Oren Harari wrote in one of his management books, "The electric light did not come from the continuous improvement of candles". Similarly, DES is a truly disruptive technology that could change the way that the world processes metal.

Chris Hinde

Chief Commentator, Mining Beacon

Previously editorial director of Mining Journal, and more recently head of S&P Global Market Intelligence's metals and mining team, Chris is now Mining Beacon's editor-in-chief and lead commentator. He posts two blogs every week, one on Monday reviewing market conditions over the prior week, and a second on Thursday looking at issues on the global mining scene. There is also a quarterly blog on business opportunities in the sector.