Modern Technologies

Today, one of the most important means of gold production involves leaching the gold ore with cyanide. The leaching process varies depending upon the character of the deposit being mined. For example, low-grade deposits impractical to mine with old technologies are now mined profitably using a process called heap leaching. In heap leaching, crushed ore is placed on a specially designed impervious pad and sprayed with a dilute solution of sodium cyanide, which percolates downward, dissolving the gold. The resultant gold-laden solution, called a leachate or pregnant solution, is then collected, clarified, filtered, and deaerated. Zinc dust added to the solution causes the dissolved gold and silver to precipitate. The recovered gold and silver are then melted in a furnace and poured into a mold. The product, a mixture of gold and silver known as dore', is sent to a precious metal refiner where the gold and silver are separated and then refined to commercial specifications.

A smelter at Panamint City, California. Bureau of Land Management.

Build a classroom heap leach operation with a pan and a mixture of sand, gravel, and sugar cubes. Spray water over the "heap" and collect the run-off solution. Allow the solution to dry. The recrystalized sugar represents the end product of the heap leach gold extraction-process.

Visit a mining operation in your community. Afterward, discuss the mine's economic and environmental implications for the local area.

Investigate environmental concerns about mining in general and the new technologies emerging to address them.

These innovative storage tanks help protect wildlife and conserve water in a modern heap-leaching operation. The gold-bearing fluids contained in the tanks are pumped to a plant for processing before the final gold pour.

Discuss what would occur if a technological innovation should make it possible to extract gold from seawater profitably. Consider the way that nations and individuals might look at "ownership" of the ocean, competition with other uses like fishing and recreation, entrepreneurial opportunities, and environmental consequences.

Consider the possibilities for mining gold on the moon. Have students write stories about a gold rush on the moon, or salvaging gold from obsolete spacecraft orbiting the Earth.

As you can see, this glittering metal does, indeed, provide golden opportunities for learning about science as well as a range of other subjects. We have only scratched the surface of gold-related topics. Your class may wish to look at additional aspects of gold or to investigate other riches from the Earth, such as silver, copper, or borax, exploring the role each has played in science and society.

Jeremy M. Brodie
Environmental Education and Volunteer Programs
Last Updated: May 1, 1996