There’s gold in them trees! Science looks to plants to find new sources of rare minerals.

Researchers at the Australian National University (ANU) are exploring how to clean up polluted water while extracting rare minerals, metals and scarce nutrients in the process.

But why start from scratch when nature has already solved the problem?

“Prospectors already look for a golden tinge to gum leaves,” plant scientist Associate Professor Caitlin Byrt told Cosmos. “Gum trees will take up and accumulate gold in their leaves. So it’s a cheap, fast, easy way to survey for new gold deposits.”

Chopping down entire eucalypt forests for a few ounces will never be economically or environmentally sustainable, nor squeezing the local koala population.

But modifying and replicating the natural processes within the trees that draw up, separate, transport and store minerals could solve a multitude of problems.

That’s the goal. And a basic understanding of how it all works has been established.

Now it’s time to turn that into a functional reality, Byrt says.

True blue ingenuity

What’s Adblue, the diesel additive got to do with it?

Australia recently experienced a crisis in the supply of the diesel additive AdBlue. Only a handful of nations, including Russia and China, produce it. The transport industry says it was plunged into crisis when it forecast a shortage.

“AdBlue is a combination of super pure water and super pure urea,” says Byrt. “But humans release a couple of grams of urea and lots of water daily as a waste product.

“What if we can get creative – where every Outback truck stop can collect deposits from drivers and return something for their diesel tanks?”

Simply put, the molecules crucial to the world’s economy are everywhere.

The numbers are enormous.

Globally it’s estimated there are three million tonnes of phosphorus, 16.6 million tonnes of nitrogen and 6.3 million tonnes of potassium locked away in urban wastewater. This includes enough organic molecules of ammonia and hydrogen to power 158 million households.

Then there’s industrial wastewater. The Australian mining industry generates 500 million tonnes each year. 

“Industrial wastewater can end up being a toxic mess,” says Byrt. “Wastewaters rich in metals like copper, lithium and iron need to be processed to recover these resources.”

Each element is immensely valuable – but only in a pure form.

The challenge is finding efficient, cost-effective ways to extract them before readily available mine deposits are depleted.

At the same time, the world’s water supplies are becoming increasingly stressed. Polluted water can’t be allowed to sit idly by.

Dr Byrt believes that represents an opportunity.

Green technology to find rare minerals

Whether algae or an acorn tree, plants are super-efficient solar-powered refineries.

Their cell membrane components can identify specific molecules, separate them from their surroundings and transport them to their desired location.

That’s what plants do. That’s how they live.

And that’s precisely what’s needed in mineral extraction and water purification.

“We’ve been studying how plants can separate different target molecules and manage them differently inside the plant tissue,” says Byrt. “But that was all for crop engineering applications, like drought resilience, salt tolerance and for advancing fundamental plant biology.”

This research is being given new applications.

“Separation processes allow you to take something that’s a problematic environmental waste and extract target resources,” says Byrt. “It has potential to enable a circular economy where those resources are reused, and you get clean water as an end product.”

That’s because plants compartmentalise their resources.

Take sugar cane. Squeeze it, and you get a sugar-rich liquid. Crush the stem, and you get a source of fibres. And the roots contain a whole separate collection of materials.

What if those otherwise unused parts of the plant could capture a valuable local mineral?

“We can engineer new membrane technologies with precision separation functions that don’t exist in any other technology. And we can do that by borrowing from what plants have already evolved.”

It’s not quite the same as plucking gold nuggets from a berry bush, says Byrt.

But it is a win, win, win scenario.

“You’re fixing carbon while using solar radiation to power the process. You’re creating a natural living environment, and you’re collecting a vital resource,” she says. “Toxic waste dumps could become lush green lithium mines. And community sewage systems are a convenient source of increasingly hard-to-find potassium, phosphorus and nitrogen.”

Hyperaccumulators

Some plants already harvest minerals and molecules on an almost industrial scale.

“There are species that can accumulate and compartmentalise up to 17 per cent nickel,” Byrt says. “So it’s entirely feasible that a hybrid accumulator could be used as solar-powered, carbon-capturing harvester in an area with a lot of gold particles spread through the environment.”

Unwanted money sinks could also become valuable commodities.

“People have said anecdotally that there may be $2 million worth of material trapped in any given mine tailings dump, but it’s creating $4 million worth of environmental headaches,” Byrt explains.

It’s only waste because it’s a messy mix of materials. And separating it has not previously been economically viable.

“It’s only valuable when it’s pure,” says Byrt. “So it’s the separation challenge that we’re trying to overcome.”

Hyperaccumulating plants already have the techniques.

It’s now a matter of adapting that into an upscaled technology.

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Also in Cosmos: When Machines Exceed Humans

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But plants themselves can’t always be the solution.

“There are some industries, like mine tailing waste, where you just can’t grow anything,” Byrt says. “There’s no living thing that’s going to survive what you’re dealing with.”

But plant know-how can still provide a solution.

“We will be borrowing from mechanisms in living organisms and converting them into machines,” she says.

Molecule manipulators

We already do this to a limited extent.

Desalination plants use membranes to take the salt out of seawater. And the US Army has shipping-container-sized portable units which can process 17,000 litres of dirty water a day into drinking water.

“Plants can already do those functions naturally,” says Byrt. “But each plant can’t do what every other plant does. It’s a matter of knowing which plants will survive what conditions and which ones will enable a particular process.”

Many species and subspecies have evolved different molecular mechanisms to suit their unique conditions.

“That means if you just take a copper-accumulating plant and expect it to work harvesting nickel-rich soil, it’s not going to work. You need the right combination of biological functions.”

The ANU research team is focusing their research on 10 target molecules.

Most are spread across nutrients such as nitrogen, phosphorus and potassium.

“Those molecules, those elements in their ionic form, come in a multitude of different complexes,” she says. “Each of these will need a specific separation process designed for it.”

The minerals being studied remain confidential for now, she adds.

“What our team do is understand, at a molecular level, what the parts of a plant are doing,” Byrt explains. “Each diverse cell type has its own biochemistry – the capability to have enzymes that might interconvert different molecules in different forms. It has also got its own membrane transport functions – allowing it to take up one thing and release another.”

Understanding this will allow anything from an algal bioreactor, a crop, a grove of trees, or a processing facility to be tuned to a particular product.

“It’s hidden in plain sight. Nature has already solved issues related to managing those sorts of resources,” Byrt concludes. “Once understood, billions of years’ worth of accrued evolved biological capability can be applied to new technologies.”