A New Zealand Startup Is Using Microbes to Suck Solid Gold Out of E-Waste

Microscopic organisms can extract precious metals from discarded devices

Photo: Johner Royalty-Free/Getty Images

The world produces 50 million tons of e-waste each year — equivalent to 4,500 Eiffel Towers or 125,000 jumbo jets — from old computers, discarded screens, broken smartphones, and damaged tablets. E-waste is the fastest growing waste stream in the world, but it also holds metals crucial to tech that could soon become short in supply.

As our reliance on tech increases, there’s a growing need to reduce e-waste while conserving metals vital to building tech products. The solution may lie in the tiniest of organisms: microbes. These microscopic life forms can extract metals such as cobalt, gold, and platinum from the devices we toss into landfills.

“Microbes can facilitate some processes that would otherwise require high temperatures and other extreme conditions,” says Anna Kaksonen, who leads the Biotechnology and Synthetic Biology Group of the Commonwealth Scientific and Industrial Research Organisation, Australia’s national science research agency. “In some cases, they provide a more sustainable alternative than traditional pyrometallurgical or hydrometallurgical processes.”

Inside Mint’s pilot plant in Auckland. Photos: Mint Innovation

Pyrometallurgy applies heat to recover metals, while hydrometallurgy uses chemicals. Bioleaching, meanwhile, employs microbes to do the job. It isn’t a novel technique — mining operators use it to extract metals from ores — but it isn’t widely used in e-waste recycling yet because it’s typically slower than conventional extraction and can’t recover as much metal as other methods. However, it holds promise as a greener process for rescuing e-waste, since heat-based methods use a lot of energy and release dangerous gases, and chemical methods produce toxic waste streams.

New Zealand-based startup Mint Innovation is one company attempting to bring microbes to the mainstream. “It came out of the idea that microbes can take a waste product and turn it into something valuable,” says Thomas Hansen, the company’s commercial manager. “Electronics have a lot of waste, so what if we could get precious metals out of them? What if we could get gold out of electronic waste?” Co-founder and CEO Will Barker previously worked at LanzaTech, a company that uses bacteria to turn factory carbon emissions into fuel that is also based in New Zealand, where waste minimization is a priority.

The company starts its gold-retrieving process by grinding printed circuit boards, RAM sticks, processors, and other metal-bearing parts of electronic devices into a sand-like powder, which goes through a leaching process that produces a liquid with all the metals dissolved in it.

“We first dissolve all the reactive base metals — such as iron, copper, and aluminum — and recover them through various processes. We use electrolysis to get copper out, for example,” Hansen says, referring to the process of using electric current to extract metals.

After that, they use microbes to extract more precious metals. “Once the base metals are out, it’s easier to get gold,” explains Hansen. “Gold is challenging to deal with chemically because it’s unreactive — it’s the last metal that gets dissolved and the first to fall out of solutions.”

“Electronics have a lot of waste, so what if we could get precious metals out of them? What if we could get gold out of electronic waste?”

The team adds aqua regia (Latin for “royal water”), a mixture of acids strong enough to dissolve gold — to the solution, then it adds the key ingredient: Cupriavidus metallidurans microbes. These tiny organisms act as a sponge, sucking up and absorbing the dissolved gold.

Next, the solution is passed through a centrifuge, which spins out the gold-heavy microbes to produce a purplish goo. “Because gold becomes purple on a nanoparticle level, you get this stuff that looks a bit like Silly Putty, with a few impurities but mainly the organic structures of the microbes and the gold,” says Hansen. This organic matter is burned off, leaving a metallic ash that undergoes traditional metallurgical processes to turn it into solid gold.

Gold is just the tip of the precious-metals iceberg. “The microbes have an affinity for other metals such as palladium, platinum, and rhodium,” Hansen says. “We want to look at not just e-waste, but any waste stream with valuable metals in it like incinerator ash from municipal waste. That might mean using different microbes or slightly changing our chemistry.”

A vanilla ice cream-like texture after the microbes have been added to the solution.
A Silly Putty-like, purplish goo after the microbes have absorbed the gold.

Researchers elsewhere are already experimenting with different organisms and approaches. A team at the Idaho National Laboratory (INL) use Gluconobacter oxydans bacteria, which produce organic acids that dissolve rare earth elements, for bioleaching. Meanwhile, researchers at the National University of Singapore (NUS) use Chromobacterium violaceum bacteria, which are capable of producing hydrogen cyanide. When placed in a solution containing gold, these bacteria bind to gold atoms and grab them.

A key difference in these approaches is that, while the INL and NUS researchers only use microbes for bioleaching, Mint Innovation uses chemicals too.

“Our understanding is that Mint Innovation is not actually using bioleaching, but rather conventional chemical leaching to extract metals from e-waste into solution, and then using microorganisms to selectively recover target metals from the aqueous metal mixture,” says Yoshiko Fujita, a senior scientist at INL. “Our research has focused on using organic acids produced by microbes from agricultural waste.” These organic acids act as a liquid medium to selectively extract metals, removing the need for additional chemicals.

The INL team has applied their approach to lithium-ion batteries, recovering cobalt, nickel, and manganese. Their ultimate goal is to support private companies who want to adopt their technology on a commercial scale, so they’re looking into ways to make it profitable.

Mint Innovation is looking to build “biorefinery” plants in cities, working with local recyclers to collect e-waste, recover metals, and make them available for reuse. The company has a pilot plant in Auckland, testing its processes on recycled IT equipment. Scaling up and going global may prove difficult, however: Alex Payne, a publicist for New Jersey-based recycling company TerraCycle, cautions that, “it may be difficult for companies to adapt to new regulations and navigate the intricacies of local environmental policies when attempting to build a physical recycling plant.”

And because it’s still partially reliant on chemical leaching, Mint Innovation must still figure out how to recycle its chemicals in addition to reducing waste and driving down its energy use.

There are kinks to work out, but the company’s closed-loop system — “the ideal recycling process in terms of supply chain sustainability,” says Payne — could be very valuable if it’s as efficient as advertised. The hope is that it’ll encourage others to prioritize recycling e-waste, too.

“With our solution, we can pay recyclers more money for the waste, then they generate more revenue from their recycling activities,” says Hansen from Mint. They’re incentivized to recycle more, and if we can incentivize better behaviors, then we can do a lot of good.”

Filipina. Freelance writer. Chocoholic. Words @ The Boston Globe, The Atlantic, BBC Travel, and more.

Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store