One method of precipitation is to add a different metal to the solution. The added metal dissolves and causes the gold to precipitate out of solution. The precipitate is collected and impurities are removed in a refinery. Another method of removing the gold from solution is to add a metal cathode. When an electrical current is applied, the positively charged gold precipitates onto the negatively charged metal cathode. In a refinery, the gold is melted off the metal cathode and impurities are removed from the melt. The remaining molten gold is poured into a mold and cooled [Ripley, Redmann, and Crowder, 1996].

Cyanide leaching produces many hazardous waste products that must be disposed of properly. Some of these hazardous materials are acids and heavy metals, but the most hazardous compounds are the cyanide compounds. The cyanide compounds are extremely toxic to most animals and can destroy an ecosystem if significant amounts of the solutions escape. If the solutions get into soils, plants absorb the cyanide-bearing solutions [Noble and Howe, 1980]. Cyanide accumulates in the plants and often proves deadly for grazing livestock.

Only with careful handling of wastes are these hazards kept from the environment. The Homestake Mine in Lead, South Dakota, is an example of a mine using cyanide leaching techniques that operates without having a negative environmental impact. The Homestake Mine produces about twelve tons of gold each year [Bachman and Caddy, 1990]. Large amounts of gold also result in large amounts of hazardous waste. At the mine, the Grizzly Gulch tailings dam is used to settle out hazardous solids and offers a large reservoir for hazardous liquids to degrade naturally. To prevent water from infiltrating the reservoir and creating more contaminated water, a trench was dug around the mine to capture surface runoff. Another trench was dug downstream to capture ground water flowing from under the reservoir. These trenches act as safety measures that isolate hazardous materials from the surrounding environment. In an effort to further reduce the amount of contaminated liquids, Homestake Mine uses water from the tailings dam in gold extraction processes. Recycling reduces the amount of fresh water that becomes contaminated by mine wastes.

Homestake Mine has shown that with careful planning and safety measures, a cyanide leaching operation does not have to contaminate the surrounding ecosystems.