Rock-Eating Bacteria "Mine" Valuable Metals

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A fairly simple process called heap bioleaching, in which copper sulfide ore is crushed and put on an impermeable pad, has also increased the bacteria's usefulness.

An acidic solution containing bacteria is applied and allowed to percolate through the heap, draining into a collecting pool.

In a few months, the bioleaching is complete, with 80 to 90 percent of copper extracted from the ore. The process can be used on ores that contain only 0.5 to one percent of copper, too little for conventional refining.

Miniscule Miners

Meanwhile, recent advances in molecular technology have allowed scientists to try to optimize the growth and function of the metal-loving microbes.

Earlier this year, lead researcher Tomita began collaborating with scientists from the Chilean venture firm BioSigma.

BioSigma was set up in part by Chile's state-owned Codelco, the world's largest copper producer.

Their goal is to make the miniscule bacterial miners speedier and more efficient by identifying key genes, proteins, and metabolites.

Tomita and colleagues, for instance, now have a better understanding of the bugs' digestive systems.

The effort has so far sequenced the genomes of three organisms that rely exclusively on either iron or sulfur—or both—as an energy source. Scientists can then grow and identify the bugs.

"We are now able to know what microorganisms are present in a sample and how many of them are alive and doing their job," says Ricardo Badilla, general manager of BioSigma. "These tools enable us to control and modify a bioleaching operation at the industrial level."

The first full industrial plant using microorganisms will begin operations by the end of 2009, and Codelco hopes to be producing over 100,000 tons of copper annually from bioleaching in the next ten years.

Environmental Boon

Bioleaching may also soften the environmental blow of the mining industry, experts say.

"Bioleaching and biooxidation processes are alternatives to conventional smelting processes, which discharge large amounts of carbon dioxide, sulfur dioxide, and several kinds of toxic materials [such as] arsenic," said Chihiro Inoue, an environmental studies professor at Tohoku University in Japan.

The methods also consume large amounts of energy resources, he added.

BioSigma's Badilla agreed bioleaching reduces the "adverse impact of mining into the environment."

"There is a tenfold decrease in gaseous emissions, a twofold reduction in energy consumption, and a fivefold reduction in water consumption in comparison with conventional … technologies," Badilla said.

Bioleaching is also cheaper: A typical operation costs only half as much as conventional smelting and refining.

But a lot more research is needed, Badilla added.

"It may take more than 15 years before bioleaching starts to gradually replace conventional technology as the process is improved."

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