Scientists at the U.S. Bureau of Mines may have discovered a way to deal with cyanide-contaminated waste from mining operations. A bacteria that occurs naturally in mine water has been found to feed on cyanide. Researchers are using the bacteria, Pseudomonas pseudoalcaligenes, to break down cyanide in heap leach solutions into carbon dioxide and ammonia. The heap leach process uses cyanide-containing solutions to dissolve gold and silver from low-grade ore. During heap leach operations, solutions are recovered and reused. The difficulty comes when mining companies want to close their mines and must dispose of the cyanide-contaminated solution without allowing it to leach into soil or groundwater. By adding nutrients, such as yeast extract, researchers can increase the bacterial population and speed up the rate at which organisms destroy cyanide. According to Richard Lien, the bureau's principal investigator for the project, two ongoing field tests in Nevada are growing the bacteria in activated carbon reactors, then circulating the solution through the reactors. A newer project, Lien says, involves applying the bacteria directly to a spent heap.