Microbes can ‘mine’ metals from toxic waste — while fighting climate change: study

Tiny organisms could help solve the massive pollution caused by mining.

Growing microbes on toxic mine waste could help companies capture pollutants while meeting the rising demand for critical minerals, a new study has found.

The paper, published on Thursday in PLOS Biology, delves deeper into the practice known as bioleaching, or the use of living organisms to pull minerals from rock, soil and waste. This process is also sometimes called “biomining.”

The researchers from Canada’s University of Waterloo found that cyanobacteria — a kind of bacteria that gets energy from light, like plants — helped bind trace metals in mine waste into more easily retrievable minerals.

As an added bonus, these techniques could help cut a sizable minority of carbon emissions from mining, the researchers wrote.

By doing so, they could help increase efficiency and reduce ecological damage from surging production of the array of minerals expected to be essential in the move to electrify transportation and the grid, the study said.

That push for electrification has long rested on a difficult paradox: Achieving the large-scale climate benefits of getting off of fossil fuels requires a huge uptick in mining — one of the most polluting sectors worldwide.

Mining is heavily polluting because it requires crushing rock to reveal ores within. These then must be pulled from the debris, often using dangerous heavy metals, in particular mercury.

Mercury is dangerous for the same reason it’s effective: It binds very effectively to metals, creating blobs of ore and mercury that can then easily be refined down into pure metal.

That stickiness, however, also means it binds into animal tissues, reaching greater and more toxic concentrations as you move up the food chain.

Sulfur and arsenic are two other toxic materials associated with metal production. Like mercury, they are easily swept into groundwater from the dumps of mining waste, known as “tailings,” according to the Environmental Protection Agency.

Those tailings contain trace amounts of valuable ores and toxic materials, but extracting one while permanently removing the other is sufficiently expensive and difficult that companies largely don’t do it, and past a certain point, regulators largely don’t make them.

Many research teams around the world are proposing using bioleaching techniques to help change that. For example, in 2020, a German team used a variety of bacteria to pull cobalt, copper and other useful metals from sulfur-containing tailings at a large copper mine.

“We can take tailings that were produced in the past and recover more resources from those waste materials,” said Jenine McCutcheon, an environmental sciences assistant professor at the University of Waterloo, in a statement.

In doing so, she added, companies can “also reduce the risk of residual metals entering into local waterways or groundwater.”

This also helps pull carbon out of the atmosphere. As the cyanobacteria grow, they speed up the process by which the pulverized rock “weathers” — pulling carbon dioxide from the atmosphere to be stored as stable carbonate minerals.

The test projects run by the researchers managed to pull down enough carbon dioxide from the atmosphere to offset about one-third of the emissions generated during mining.

That makes the technology “a potential game-changer in the fight against climate change,” McCutcheon said.

That could mean that legacy mine sites get a second life as their once-worthless tailings become cost-effective sources of new materials.

For new mines, she said, the possibilities are even greater.

Integrating bioleaching processes with cyanobacteria at the start of production could “result in mines that are carbon neutral from the get-go rather than thinking about carbon storage as an add-on at the end,” she said.

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