How to purify gold

When gold is mined, it often contains other metals, such as zinc, copper silver or iron. To get rid of the impurities, gold processors must purify their gold.

Before gold is purified, it must be extracted from ore. One method of extraction is amalgamation. This process uses mercury to dissolve gold from an ore.

In amalgamation, mercury is applied to an ore, the mercury picks up the gold from the ore and the result, called an amalgam, is then distilled. The mercury is boiled off from the amalgam to remove it from the gold. This is a very expensive process, as mercury is toxic and environmentally hazardous and must be handled with great care.

Cyanidation can be used to separate gold from ores in a process known as vat leaching.This involves contacting gold ore with a solution of sodium cyanide in large vats or tanks. The gold present in the ore then enters into solution. Lesser quality ores must be subjected to heap leaching, which requires repeated spraying of ore with cyanide solution over a longer period of time.

Once gold is extracted from ore, it must be purified. There are two methods most commonly used in this process, known as the Miller and Wohwill processes. The Miller Process melts gold and blows gaseous chlorine into the molten gold. The impurities present in the gold form a layer of chloride compounds on the surface of the liquid gold that can be removed.

The Miller process is easy and can be employed quickly, but will only produce 99.5 percent pure gold. The Wohlwill process is more expensive, but produces purer gold.

In the Wohlwill process, electrolysis is used to purify gold. Impure gold is placed in a solution of hydrochloric acid and gold chloride. An electric current is then passed through the gold, causing the impurities in the gold to move into the solution or sink to the bottom of the tank as sludge. This process can produce gold with a purity of about 99.99 percent, but also is costly.

Gold has become a hot investment commodity in recent years as investors have flocked to the precious metal as a means of hedging against declining stocks and other investments. In fact, the price of gold has appreciated considerably in the last four years and recently passed the $1,300 per ounce mark.

Because of the gold boom, gold refining and processing companies are likely to see increased profits as demand for high quality gold increases. For investors, gold-related companies may be a solid investment during these troubled economic times.

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