Amalgamation

AMALGAMATION (EN: amalgamation; DE: Amalgamation, Amalgamieren, Amalgamierung, Quicken; FR: amalgamation; ES: amalgamacion; RU: амальгамация) is the process of selective extraction of metals (mostly noble) from ores, which is based on the ability of metals to form alloys (amalgams) with mercury during the wetting of these metals by mercury. Amalgamation is known for more than 2000 years. The description of the process has been given by G.Agricola during the 16th century. Till the 20-ies of the 20th century.

Amalgamation is the leading process during the extraction of the precious metals. It is used since 50-ies mainly during the processing of the gravity concentrates (there are more effective for the ores the flotation and cyanidation).

The internal amalgamation is performed simultaneously with the grinding of the ore within the runner bowls or mills, the external amalgamation is performed at the gateways: during the movement of the pulp, metals are trapped by the mercury, which is deposited onto the copper (sometimes silver) sheets. They conduct the amalgamation of the gold-silver ore within the alkaline medium, of the platinum ore within the acidic medium with the presence of the zinc amalgam.

Electrical amalgamation is the type of amalgamation, during which the wettability is improved by the impact of the direct current: the negative charge is given to the mercury at the gateway, the positive charge is given to the pulp. Depending on the ratio of the mercury and metal, the amalgam at the room temperature may be liquid, semiliquid, or solid. The excess of the mercury is removed from the liquid and semiliquid amalgams by the filtration through suede under pressure.

Amalgamation has got the widest distribution for the extraction of gold. The solid amalgam, which is containing 40-60% of gold, decomposes by the heating to 750-800 degrees Celsius; mercury is distilled and returned to the process. The extraction of gold into amalgam (depends on the degree of the opening of the surface of the metal) sometimes reaches 99%; 0.1-1% of mercury remains within the spongy gold, which is obtained. The losses amount to 6-7 grams per tonne of concentrate. They subject the spongy gold to melting.

The decrease of the volume of the usage of amalgamation has been caused by the low ratio of the extraction of the certain forms of gold during the presence of sulfides, especially of the pyrrhotite. The disadvantages of the amalgamation are the difficulty of the ensuring of the occupational safety during the work with mercury, and the possibility of contamination of the environment, the advantage is the possibility of the direct and quick obtainment of gold during the single process.