With the global demand for lithium forecasted to exceed current production rates in 2022, the industry is hard at work developing not just more efficient but also more environmentally friendly methods of extraction. Furthermore, with the current production heavily concentrated in a few regions - with China, South America, and Australia being the main producers - many countries are eager to develop their own supply. One of the methods explored is extraction from geothermal fluids, an option currently pursued in a new test project in the UK.

The continuously increasing demand for renewable energy is simultaneously creating new challenges and new opportunities for the global drilling industry. One of the areas experiencing a significant increase in demand is the extraction of the rare minerals and metals intrinsic to green technologies and the renewable energy infrastructure. In particular, the rise of electric vehicles has meant that lithium, used in lithium-ion batteries, has become one of the most sought-after commodities on the planet.

A study by the University of Technology Sydney (UTS) shows that the demand for the minerals and metals could outstrip current production rates for key metals by as early as 2022. The study concludes that cobalt, lithium and rare earths are the metals of most concern for increasing demand and supply risks, a supposition which is echoed by the industry with Jeremy Wrathall, chief executive of the newly established UK venture Cornish Lithium and a mining analyst at Investec saying: "Lithium demand will exceed supply for the foreseeable future and I don't think the industry can cope."

Drilling the dirt off clean energy

With the increased demand for lithium an increased public focus on the environmental impact of the different methods of extraction has also followed. Consequently, with the main increase in demand for lithium due to come from the electric vehicle industry, it is likely that the market's major players will seek to strengthen their standing with environmentally and ethically conscious buyers by sourcing lithium from regions and sites where production is done in a socially, economically and environmentally sustainable manner.

According to the report by UTS, currently, one of the major concerns over lithium production is water contamination and shortages in Argentina, Bolivia and Chile, where lithium is extracted from continental salar brines.

Furthermore, the study by UTS shows that as demand for minerals such as lithium skyrockets, the already significant recognised environmental impact of hard rock mining, which supplies the large share of lithium sourced in Australia, is likely to rise as well. This is why Earthwork, the US non-profit organisation that commissioned the study, is calling for a shift in the clean technologies sector towards more responsible minerals sourcing.

"We have an opportunity, if we act now, to ensure that our emerging clean energy economy is truly clean - as well as just and equitable - and not dependent on dirty mining," says Payal Sampat, Earthworks Mining director. "As we scale up clean energy technologies in pursuit of our necessarily ambitious climate goals, we must protect community health, water, human rights and the environment."

By exploring new methods of profitably sourcing lithium in more environmentally responsible ways, many in the industry seem to be attempting to meet the demand.

Could Cornwall's underground provide a cleaner source of lithium?

First discovered by miners in 1864, the existence of Cornwall's lithium-enriched geothermal fluids can be ascribed to the fact that significant areas of the county are underlain by a body of lithium-rich granite. Continuous interactions with the rocks, which remain hot at depths, has resulted in lithium-enriched geothermal fluids. It is by extracting lithium from these fluids, found deep beneath the surface of Cornwall's granite, that Cornish Lithium hopes to establish a high-tech, environmentally responsible mining industry.

To establish the economic viability of extracting lithium from these waters, Cornish Lithium is currently drilling two test boreholes of approximately 1,000m deep and 120mm width. The research boreholes will intercept permeable geological structures below the area's known historic mine workings.

 

"Our geologists will take samples of geothermal waters from these permeable structures to measure the amount of lithium that they contain," explains Cornish Lithium's drilling manager, Mike Round.

Cornish Lithium believes that access to these fluids can be gained via extraction boreholes, and that lithium can be extracted at surface in a small processing plant using advanced technologies such as ion-exchange membranes or reverse osmosis.

How can it be done?

While Cornish Lithium is still at an early stage of exploration and has not decided the exact process, a number of similar proprietary processes have been developed by companies such as Posco, Rincon (formerly Enirgi Group), Veolia, Tenova, PurLucid and Eramet.

Indeed, the demand for responsibly- and locally-sourced minerals has led to much research into the developments of new methods of lithium extraction including developments which might be used to profitably extract lithium directly from lithium-rich geothermal fluids.

However, most methods depend on adsorption or ion exchange on a surface. In a paper for the World Geothermal Congress in Reykjavik, 2020 (Pálsdóttir et al. Valorization of Geothermal Waters: the Development and Testing of a Supercritical Fluid Extraction Process for the Recovery of Lithium*), Arna Pálsdóttir, a chemical engineering specialist points out some weaknesses of these methods: "Because of the dependence on surfaces, scaling can be severely detrimental to activity, and silica removal is required for the processes to operate. Additionally, there has been a lack of focus on the concentration process necessary to make geothermal waters feasible for the production of lithium products, which are generally made from brines that have been concentrated to about 4,000-6,000mg/L."

In the papers she and her colleagues present an alternative method, a supercritical fluid extraction process, stating: "Compared to conventional lithium extraction and concentration methods, a supercritical fluid extraction process is faster, more environmentally friendly and not sensitive to silica scaling. By using a lithium selective crown ether extractant dissolved in supercritical carbon dioxide the extraction process takes about an hour and results in significant concentration of lithium into an aqueous solution. It takes place across a fluid interface at pressures and temperatures sufficient to both prevent silica scaling and limit the effect of scaling if it happens. The overall extraction efficiency of lithium from a 10mg/L synthetic geothermal water solution is 30 per cent in a batch operated process, at 60C and 250 bars."

The possibility of extracting lithium with new technologies such as this unlocks new potentials for existing geothermal ventures, but also for the creation of new ventures of lithium extraction plants possibly doubling as geothermal energy or heating plants.

Lithium extraction the facts

Extraction of lithium from hard rock ore mining (spodumene, petalite, and lepidolite) requires various hydrometallurgical processes. Because of the high energy consumption and amount of materials required, it is a more costly but also more reliable process than lithium brine extraction by evaporation.

In order to extract lithium from salar brines, the salt-rich waters must first be pumped to the surface into a series of evaporation ponds where solar evaporation occurs over a number of months. Because salar brines occur naturally at high altitudes — and often in arid and remote areas — solar evaporation is a cost-effective method for precipitating salts.

However, as they are dependent on climate, solar evaporation techniques are highly unreliable, generate significant volumes of waste and, crucially use large amounts water in areas where water is already a scarce and highly valuable resource.

 

 

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 Geothermal Waters: the Development and Testing of a Supercritical Fluid Extraction Process for the Recovery of Lithium is to be presented at the World Geothermal Congress, Reykjavik, 2020.