These metal munching bacteria might help solve mining’s toxic waste problem

You might not think you want a metal eating bacteria in your life, but if you live near an abandoned mine or smelting plant then you definitely do because if this latest breakthrough is anything to go by then this new strain of bacteria could help clean up all the toxic metals in the environment and make it a much safer place to live.

A special type of bacteria can "eat" a nail in just three days, says a biotechnologist from Chile. Nadac Reales, who studies the microorganisms from her lab in the industrial town of Antofagasta, hopes to use the bacteria to clean up mining waste in her home country, which is the top global producer of copper.

As odd as it sounds, if it pans out, her method could also help clean up the waste left behind from current and legacy mining operations in the US. That should be a major priority: mining sites dump over 50 million gallons of wastewater containing arsenic, lead, and other toxic metals into our rivers and streams on a daily basis, according to a 2019 report from the Associated Press.

Unlike the rumors about Coke or Diet Coke dissolving nails, this metal-eater is legit. In her research, Reales places regular construction nails into a liquid that contains the metal-eating bacteria, called Leptospirillum ferriphilum. After just three days, any trace of the nail is gone; what's left is a solution called a lixiviant - a liquid used in metallurgy to leach pure ore from rock sources.

These bacteria oxidize metals like iron, basically inducing the same disintegration that takes place during rusting. At first, Reales told AFP, the bacteria took as long as two months to dissolve a nail. That's still an impressive result, but it was much too slow for the practical applications Reales envisioned.

So, she sped up the reaction by starving the bacteria, effectively revving up their internal clocks to take in whatever nutrition they could in the shortest possible time. This worked, cutting the timeframe down from two months to just three days. Next, Reales told AFP, she plans to test the bacterial mix on larger pieces of metal equipment to see how it works.

That could be a game-changer for Chile's mining industry.

"Some metals can be recycled in smelting plants but others, such as HGV truck hoppers that can hold 50 tons of rock, cannot and are often discarded in Chile's Atacama desert, home to the majority of the country's mining industry," AFP reports.

Mining pollution varies by the type of operation - open-pit mining, underground mining, brine mining, etc - but all of them create their own environmental hazards. In some cases, large, solid scraps of metal are left behind from the smelting process (extracting metal from ore through heating and melting). Reales' method is likely most effective for those large slabs of metal.

More broadly, mining produces hard-to-capture metal and mineral dust, which are carried away with wastewater. When companies conduct open-pit mining, for instance, they release mineral and metal dust into the air, which can accumulate in the water and in local wildlife. The dust can also release radioactive chemicals that can flow back into the ground and further into the bedrock.

Traditional underground mining has many of the same problems as open-pit mining as far as releasing particulates into the air and water, but it can also weaken the actual ground due to the extensive tunnelling and blasts. When underground mines rely on mercury as an enabling tool to extract ore, that mercury can also leach into the ground and water.

In-situ leach mining is like underground mining except that fluid is used to help dissolve and extract ore. This is a positive in that it circumvents processes that release harmful dust and other particulate matter, but there's still leftover - usually very acidic - fluid that can damage the surrounding ground. Heap leaching is similar to in-situ leaching, but the difference is that all of the fluid is applied in the open air and is less contained.

Where does that leave Reales' technology? For that, we have to go back to the beginning - to the lixiviant left behind by the extremophile bacteria. This fluid can be used to extract copper, replacing other damaging acids and chemicals that are currently used in leach-based mining processes.

So, as long as there are discarded metal objects to dissolve, a plentiful supply of lixiviant can step in to lessen the environmental impacts of leach mining. Reales says this will make green mining more of a possibility in her home of Chile. Time will tell if her process can take shape in the US too.