Merrill–Crowe process

The Merrill -Crowe process is a separation technique to remove gold and silver and copper from a cyanide solution.

The separation of the rock from the gold - cyanide solution is obtained by filtration or counter-current decanter. Thereafter, the solution is passed through special filters, which are usually made ​​of diatomaceous earth. The atmospheric oxygen contained in the solution is then removed in a vacuum release system. Hurls In this system, for example, a rotating distributor disk the solution evenly as a thin film on the inner vessel wall. Expanding by the vacuum in the tank and burst, the air bubbles contained in the solution and are filtered off with suction from the vacuum pump.

Subsequently, zinc dust is added to the purified, oxygen-free solution. Since zinc against gold has a higher chemical affinity for cyanide, the gold settles out. If silver or copper to be present in the solution, this set by the addition of zinc dust also.

The remote precious metal is filtered from the solution and treated with sulfuric acid to give zinc remains in solution. This solution is filtered again and melted the remaining gold billets. Further purification of the rough bar is carried in a metal refining process that removes the metal impurities contained in the gold, such as copper or silver, and produces the desired degree of purity of the gold.

The basic process was invented by Charles Washington Merrill around 1900 and patented; later he was by Thomas B. Crowe, who worked for the Merrill Company, improved.

Today Electrometallurgy is an alternative to the Merrill -Crowe process.