'Biomining': metal-munching microbes may help recover mineral ore

TOMORROW'S gold may be mined by bugs - real gold bugs. Advances in the rapidly emerging field of biotechnology are leading to the development of new drugs and ''supercrops'' - plants, for instance, that may thrive without fertilizers.

But quietly, some researchers are also working to harness this new technology for more esoteric but still important chores, including mining metals and minerals.

The thrust: to use existing bacteria and genetically engineered organisms to help refine and recover metals such as gold, silver, copper, and uranium - and to help clean up industrial pollutants.

Most of the research is experimental enough that metal-munching microbes won't be working alongside draglines for several years yet, if then. But, by one estimate, ''biomining'' could be a $5 billion-a-year enterprise by the turn of the century.

''The level of effort nationwide has really been intensifying the past couple of years,'' says John Spisak, vice-president of operations at Denver-based Anschutz Mining Corporation.

The allure of microbial mining lies largely in what it won't do. In theory, it will allow companies to extract metals without all the smoke-belching of smelters. It also is a less energy-intensive process. And it offers the potential of recouping riches from low-grade, uneconomic ores.

The idea is far from new. Bacterial methods are used to mine some uranium, mainly in Canada. These methods have long been used to ''leach'' copper from low-grade ores. Biological processing accounts for as much as 20 percent of the copper produced in the US each year.

Organisms already present in the ore usually do the work. First, water is sprayed over piles of low-grade ore or tailings to encourage the growth of the metal-extracting microbes. The water picks up oxygen from the air and acids from the rock as it percolates through the rubble. Both are essential for the bacteria to flourish.

The solution is recycled through the pile or tailings, causing the organisms to multiply. These then break down the metal-containing minerals in the rock, which dissolve into the solution. The effluent is treated to remove the copper when the concentration becomes high enough.

What scientists want to do now is apply the technology to higher-grade ores as well as other minerals. Scientists at BC Research, for instance, a firm in Vancouver, British Columbia, believe they have devised a copper extraction process that will compete with conventional smelting and chemical refining techniques.

Other researchers are focusing on using bacterial methods to recoup other metals. Anschutz Mining, for example, recently carried out tests on microbial recovery of cobalt, nickel, and copper. The results were ''promising,'' says Mr. Spisak, though similar work on tungsten proved disappointing.

Another area - precious metals - may hold the most near-term promise for bacterial rock crunching. Given the depressed state of the metals market in general, many researchers are looking at areas where the payoffs may be biggest. Work on recovering gold, silver, and platinum from ores and low-grade tailings is moving ahead in South Africa, Canada, and the United States among other places.

Booty can also be found, however, not in just what miners dig up, but in what they discard. Thus interest is mounting to use microbes in retrieving precious and strategic metals from waste water. There's plenty of potential here: Some 25 different industries flush about $100 million worth of gold, silver, and other metals into waste streams each year. Likely targets for clean-up: photographic and electronics firms, jewelerymakers, mining companies, and foundries.

If metals can be plucked out for salvage, they can also be removed for pollution control - another focus of microbial research. Organisms have long been used for devouring organic wastes in municipal waste-treatment systems, and , more recently, in cleaning up toxic chemicals. Now solutions are being sought to absorb toxic metals. Advanced Mineral Technologies Inc., a small New Mexico firm, expects to hatch a commercial waste-water treatment system within two years.

None of these elixirs, however, will yield results overnight. Different bacteria will have to be found for different minerals and deposits. And these strains of bacteria are also subject to the vagaries of the natural world: They have to be made to withstand cold, heat, and the toxic materials naturally present in the environment. ''There is not one nice little recipe involved like making biscuits,'' says Don Seidel, a US Bureau of Mines researcher in Salt Lake City.

The mining industry, for its part, doesn't have the money to tinker with new technologies - even if it is interested in trying them. A few companies remain dubious, anyway. Republic Steel Corporation looked into using microbes for cleaning up acid streams at its coal mines. ''It was too complicated for our operations,'' says Edwin Kawasaki, Republic's assistant research director.

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