Biohydrometallurgy is a technique by which microorganisms are used to recover certain metals from ores. The technique was first used over 300 years ago to extract copper from low-grade ores. In recent years, its use has been extended to the recovery of uranium and gold, and scientist believe that it will eventually be applied to the recovery of other metals such as lead, nickel, and zinc.

In most cases, biohydrometallurgy is employed when conventional mining procedures are too expensive or ineffective in recovering a metal. For example, dumps of unwanted waste materials are created when copper is mined by traditional methods. These wastes consist primarily of rock, gravel, sand, and other materials that are removed in order to reach the metal ore itself. But the wastes also contain very low concentrations (less than 0.5%) of copper ore.

Until recently, the concentrations of copper ore in a dump were too low...