Seloxium seeks to pluck precious metals from mine effluent

If everything goes to plan at the start-up Seloxium, mining companies and others seeking to recover precious metals and rare earth elements from wastewater will soon have the option of better—and cheaper—technology.

Spun out of the University of Oxford in 2022, Seloxium is commercializing Selectal, a liquid-phase polymer that can be combined with additives such as surfactants to selectively isolate metals in effluent from sources as diverse as agriculture, mining, and heavy industry.

Seloxium won’t disclose the polymers and other reagents it works with but says it tailors them to bond preferentially to a specific target metal—say, gold or platinum—in a given effluent. Next, the metal-laden particles are filtered from the wastewater; the purified and concentrated target metal is then isolated from the polymer and precipitant.

Existing approaches such as electrochemistry, ion-exchange resins, and membrane filtration come up short in one way or another, says Seloxium cofounder and CEO Christian Peters, who has a PhD in water treatment. “You need a technology that has three things: it has to be extremely fast to handle the large volumes; it needs to be robust and not foul up; and it needs to be very selective.” Selectal checks all the boxes.

Two of Seloxium’s cofounders, industrial chemist Steve Colley and University of Oxford professor Nick Hankins, are among the inventors on a worldwide patent published in 2022 that forms the basis of the company’s technology. In the patent description, the inventors state that their technology could cost-effectively treat effluent at concentrations as low as 1 mg/L. The Oxford connection runs deep in the company. Peters is a fellow at the university and supervises PhD students there.

Seloxium’s initial target is mining effluent, which is complex and contains mixtures specific to each mine. This complexity makes mine wastewater difficult to process. “It can take weeks to months to find the right reagents that work under certain conditions,” Peters says. “We have tested many real-world samples from customers in the rare earth, gold, and platinum group metals space and have successfully demonstrated several proof of concepts.”

Seloxium is one of a number of start-ups around the world developing chemistries for extracting precious metals from mining effluent. Salt Lake City–based GlycoSurf, for example, is extracting rare earths and other critical minerals using glycolipid surfactants. In one project, GlycoSurf developed a surfactant that binds with a target metal, forming bubbles that are laden with the metal. To separate it from the effluent, “we collect the foamate,” GlycoSurf CEO Chett J. Boxley says in an email.

Seloxium has proved its technology at pilot scale by recovering rare earth metals and aluminum from mine effluent, as well as platinum group metals from industrial waste, at its facility in Wilton, England, on a site formerly owned by the chemical pioneer ICI. In the tests, the company recovered 96–98% of a target metal present at parts per million concentrations in thousands of liters of effluent in a single step, according to Peters.

“We are at the stage of starting to test tonnage scale,” Peters says. Beyond this scale, Seloxium will seek to build modular reactors on its customers’ sites. Because its reagents must be tailored to a specific effluent, Seloxium expects that it will become an active partner with customers rather than a technology licensor.

Seloxium’s staff of just under 20 people is packed with chemists and engineers. Even the office manager, Hans Cook, has a master’s degree in chemistry. In an indication of where the company is headed, several Seloxium employees were involved with the mining industry before joining.

Peters and his colleagues have raised $10.8 million from investors, including the precious metals refiner MKS Pamp, and have secured three grants totaling about $4.0 million from the government agency Innovate UK. To take its processes to commercial scale, Seloxium plans to raise up to $27.0 million more in series A funding. Some of that money will pay for additional staff. “We will need skilled operators, engineers, and project managers,” Peters says.

Seloxium runs wet labs in Oxford. In addition to coming up with the right reagents for purifying a target metal in a particular effluent stream, the research team there has been exploring how to recycle the reagents. “But that’s not something we have scaled to date,” Peters says.

Seloxium also has ambitions to help mining companies reduce their environmental and financial liabilities by making it cost effective for them to recover precious metals from sludge in dammed-up tailing ponds. Thousands of such ponds exist around the world.

“These dams have broken in South America, South Africa and have killed people,” Peters says. “They are a huge liability. We want to change these tailings from a liability to assets.”

Alex Scott is a C&EN business reporter covering all chemistry-related issues in Europe.

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