UK first: Cornish Lithium trials direct extraction of key battery metal from geothermal waters

Cornish Lithium

AT the end of March, Cornish Lithium commissioned the UK’s first direct lithium extraction pilot plant, as the company pushes to produce an element that is critical to the clean energy transition. There are also plans to provide geothermal heat from the water to local industries. We caught up with members of the development team to discuss the project in more detail, including their expectations that the production process will provide significant benefits over traditional lithium extraction techniques.

Cornish Lithium’s goal is to drill a series of wells across Cornwall to pump out natural lithium-rich geothermal waters found around 2 km beneath the surface of the Earth. Modular process plants built alongside these wells will recover the lithium through a technique called direct lithium extraction (DLE) that promises faster recovery speeds, smaller industrial facilities and less energy use than traditional techniques.

Less water, less energy, less space

“DLE is an umbrella term for a whole series of processes for extracting lithium directly from waters,” says Cornish Lithium Geochemist Rebecca Paisley. Evaporative processes common in South America are typically used to recover lithium from geothermal waters.

“They pump the waters to the surface to these evaporation ponds that are 5–10 km across. It sits there for two years. You get about 50% recovery of lithium. DLE looks at removing that need for an evaporation pond. The process takes 1–3 hours rather than years.

“If we need any water in our process, because we’re bringing up geothermal water from under the surface we can make our own clean water. Compare that to in South America where you’re losing the water in an already water-scarce environment.”

There are also more traditional mining processes used to recover lithium bound up in hard rocks but these are energy-intensive as the rocks have to be crushed, ground and heated.

Given the benefits, you’d be forgiven for wondering why the technology has not been applied until now. Paisley notes that companies developing DLE technology began forming around ten years ago when it became apparent that there was going to be a significant shift to electric cars and a huge increase in demand for lithium for their batteries.

“In 2030, any new car you buy in the UK has to be electric. And it takes on average ten years from finding a deposit to mining a deposit. So that lithium needs to have been found two years ago. That is why we’re seeing a massive demand for lithium,” Paisley says.

Richard Thompson, a chemical engineer who is project managing the development of Cornish Lithium’s pilot plant, says DLE is being adapted using techniques already used elsewhere.

“DLE technology relies on three unit operations: ion exchange, absorption or adsorption. They’re all well known. They are just being adjusted to act as DLE-type technologies as well.”

The company’s £4.2m (US$5.4m) pilot plant, which has received £2.9m of Government funding, has been built at its geothermal water test site in United Downs in Cornwall and is trialling a DLE technology provided by French firm GeoLith.

Thompson says: “The commissioned pilot plant has a pre-treatment process for the geothermal water, which includes filtering, pH adjustment and temperature control. Thereafter, the water is passed through the DLE Li-Capt process provided by GeoLith, where lithium is absorbed onto fine filaments, using a selective surface chemical. Once saturated, the filaments are desorbed using hydrochloric acid, rinsed and brought back into operation. The DLE absorption, desorption and rinsing is operated as a continuous process, in a series of vessels. The concentrated lithium chloride eluate will be stored for additional refining testwork, whilst the depleted brine is disposed of in an environmentally safe manner.”

The process is operated at low pressure, around 1–2 barg. The pipework and vessels have been fabricated from PVC. Thompson says all concentrated acid and alkali pipework is pipe-in-pipe, to prevent leakage to the environment and harm to personnel.

“The pilot plant has been designed to be as flexible as possible and is contained in standard 20 ft containers, so that it can be located at different sites, as additional boreholes are trialled across Cornwall, for lithium recovery.”

Picking a partner

The team will test various DLE technologies at the plant throughout 2022.Thompson says they aim to commercialise production within two years, so there is a need to make a final decision on a technology partner by the end of the year. Thompson would not be drawn on the volumes of lithium that the company plans to produce. The operation would involve extracting water from a production well, extracting the lithium and then pumping the water back down a separate disposal well. The company would then transport concentrated lithium in solution from its decentralised processing plants to a central refinery to produce lithium concentrate.

On risks, Paisley says she is confident that the operations will not impact surface groundwaters due to the depths they are drilling; that the reagents added to remove lithium will not be an environmental issue; and notes that the company is working with relevant authorities to ensure they are complying with necessary environmental and safety requirements. From a process engineering perspective, Thompson says the key challenges are ensuring the technology they pick can cope with other components of the groundwater, including silicates, and scaling the technology for higher throughput. Paisley notes that fortunately, the geothermal waters are “incredibly benign” containing relatively low levels of iron and dissolved solids that would hamper downstream processing.

Finally, the company plans to work with others on using the 75°C water to provide heat to local industries, including in the food and water sectors.

“We’re looking at how we can work with partners across the south west. We can provide heat partly for our own processes but also to allow them to decarbonise their processes.

“It’s a really exciting time for Cornwall. The potential for the mining industry to revitalise the county has been picked up by a lot of relevant authorities, and we hope that this will be the start of something new.”