Biomining: How microbes help to mine copper

By Katia Moskvitch
Technology reporter, BBC News, Santiago, Chile

  • Published

Say bacteria. People think infection. Or yogurts.

But in Chile, bacteria are being used to get at something this country heavily depends on: copper.

Chile is the world's biggest copper exporter, and has the planet's largest known reserves of the red metal.

The Atacama Desert, a desolate rocky plateau west of the Andes mountains, is dotted with copper mines.

Every now and then, a mining train passes through the arid landscape. Here and there the ruins of tiny towns still stand where miners used to live decades ago, their mud huts gradually falling to pieces under the baking sun.

Export of the metal is essential for Chile's economy - it amounts to about 70% of all Chilean exports - and the more copper the country digs out, the more money pours in.

The demand for the metal is continually increasing too; copper is used in most of our lives, from electrical wires and telephone lines to roofing materials, from nutritional supplements to jewellery.

It is thought that the element was created billions of years ago in the stars and then became part of the materials that formed the Earth. Volcanoes and other activity caused by the planet's shifting tectonic plates then brought it closer to the surface

Image caption,
Chile is the world's biggest copper exporter, and a mining train is a usual sight in the Atacama Desert

To get it out, you normally have to dig.

Then, to separate copper from ore - the rocks containing it - you have to crush and grind, and then apply sweltering heat and toxic chemicals.

These conventional mining methods are very energy-intensive and thus expensive, and therefore only used on sites where it is estimated that the concentration of copper - called grade - is actually worth spending that much money on its extraction.

Bacteria on board

But as people have been hunting for the Earth's minerals for centuries, high-grade copper sites have become scarce.

In the past there were deposits that contained as much as 30% of the red metal. Now many have grades of 1% to 1.8%.

But even when a mine is estimated to contain high-grade ores, the bulk of the material coming out of the pit has a grade below 1%, and is usually discarded as waste.

Unless mini-miners come to help - microbes.

Biosigma is a biotechnology venture set up by Codelco, a Chilean state-owned corporation and the largest copper mining company in the world, together with Japanese firm Nippon Metals and Mining.

Based on the outskirts of Santiago, Biosigma is one of only a handful of biomining companies around the world.

In the main lab, chemists and biologists in white coats and goggles are busy transferring colourful liquids from flasks to tubes and performing peculiar tests in front of an open oven with raging fire.

All the flasks, tubes, containers and huge tanks are full of microbes: Acidithiobacillus ferrooxidans and Thiobacillus ferrooxidans bacteria, harnessed by the firm to break down minerals in order to improve copper recovery rates and reduce operating costs.

"We know that conventional mining methods are not used for low-grade materials that simply get dumped - so the only way to get copper from them is by using new knowledge and capacities - in this case, biotech," says Ricardo Badilla, chief executive of Biosigma.

Using bacteria can result in extracting as much as 90% of the total metal at a pit mine, instead of merely 60%, he adds.

Image caption,
Bioleaching is an alternative method to traditional mining techniques

But how can microbes help get copper from a rock?

As Pilar Parada, research and development director of Biosigma, walks past a weird-looking installation with wildly shaking flasks, she says the key to success is using microorganisms that are naturally present at mining sites.

"These bacteria need very little to do their work, they use air and mainly oxygen and CO2, and use the mineral itself as a source of energy," she says.

She explains that if a mining site is left alone, microorganisms would eventually liberate copper from rocks, but it could take hundreds of years.

To speed up the process in a biomining lab, scientists use bioleaching.

Ores are placed into acid, and then researchers introduce bacteria that change the solution so that it dismantles the rock and frees copper, in liquid form.

And after a special electrochemical process, it is then turned into solid metal that can be used in the industrial applications we so much depend on.

Future of mining

Some call biomining the "mining of the future".

Indeed, it is much cheaper and greener than traditional mining - there are a lot fewer CO2 emissions and carbon and water footprints are lower than using conventional technology.

Furthermore, the toxic chemicals used in traditional mining can be extremely harmful to the environment; there have been accidents before. In the case of biomining, the bacteria are naturally occurring at mining sites anyway, and are not pathogenic.

Biomining is already in use in several countries, including South Africa, Brazil and Australia. Overall, some 20% of the world's copper production comes from bioleaching.

The practice is not limited to copper. Microorganisms are also used to extract gold and uranium. And there are other applications of biomining: scientists are working on using microbes to clean up the corrosive acid pollution left over in mining waste.

But Gabriel Rodriguez, the director for energy, science, technology and innovation at Chile's Ministry of Foreign Affairs, says that the technology needs help to develop.

"There are still not enough microorganisms for doing that job, so more research needs to be done," he says.

"And this is exactly the bet that Chile has been making in the last years.

Image caption,
The 33 miners trapped at the San Jose copper and gold mine had a lucky escape

"But our bet is also to export the technology, so that the world can move from just exploiting natural resources to adding a value with the help of biotech."

If it works, one day it might be possible to get mine for copper without digging huge pit mines. Instead, miners would simply drill two holes to introduce a solution full of microbes, and then collect it once it contains copper.

This alternative to traditional mining could even help save lives - estimates suggest that some 12,000 people die from mining accidents around the world each year.

The 33 miners who spent 69 days trapped at 700m below the surface at a copper and gold mine in Chile's Copiapo region in 2010 had a lucky escape; not everyone is that lucky.

If microbes take over, the bacteria won't die if they get trapped.

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