Puricare Industrial Enterprises: GOLD AND SILVER RECOVERY - Mercury Amalgamation - Amalgamation is a concentrating process in which metallic gold or silver, or an alloy of the two, is mixed with mercury, either in a amalgamation drum, or on an amalgamation table, where the precious metal bonds with the mercury to form the metal laden mercury AMALGAM and the waste (barren) ore pulp are caused to travel different paths to effect separation.

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Gold And Silver

Recovery

Mercury Amalgamation

Amalgamation is a concentrating process in which metallic gold or silver, or an alloy of the two, is mixed with mercury, either in a amalgamation drum, or on an amalgamation table, where the precious metal bonds with the mercury to form the metal laden mercury AMALGAM and the waste (barren) ore pulp are caused to travel different paths to effect separation.

The ore containing the precious metals should be ground fine enough to allow the maximum exposure of the gold or silver surface to the mercury (usually between 100 mesh and 325 mesh).

Often, water is used as the ore is mixed with water to help disperse the ore and to promote a better precious metal to mercury interface.

Sulfide precious metal ores are difficult to amalgamate using mercury, due to the complex iron-sulfur-gold and other metals present, which do not allow the gold to come into contact with the mercury.

It is not uncommon for only 20% to 30% recovery of gold and silver by mercury amalgamation from sulfide ores.

Precious metals are recovered from the mercury by retorting the mercury.

Retorting consists in distilling off the mercury from the amalgam and is done in a cast iron retort or steel retort, a vessel having a cover which can be fastened on so tightly that no fumes of mercury escape, except by the condenser, which leads from the cover to a vessel containing water, where the fumes of mercury are condensed to a metallic state.

The condenser has a water jacket surrounding it, through which a small quantity of cold water is continuously passed during the operation.

The open end of the vapor pipe must be lower than where it emerges from the discharge of the retort, and its open end is submerged in water during the distilling operation.

The retort should not be filled much over half full, of amalgam, as room is required for the vaporized mercury.

It is good practice to make the amalgam into several small balls, thus allowing the mercury to vaporize more rapidly.

The distillation is performed at a very low temperature and heat applied very gradually, until 1,500 deg F is reached.

It usually takes 2 hours to retort the amalgam, once the 1500 deg F temperature is reached.

DANGER! It should be noted that mercury is very poisonous to humans and many forms of life.

The warning below is from the material Safety Data Sheet, which comes with every shipment of mercury.

MAY BE FATAL IF INHALED OR SWALLOWED.

CAUSES RESPIRATORY TRACT, EYE AND SKIN IRRITATION.

MAY CAUSE EYE AND SKIN BURNS.

HARMFUL IF ABSORBED THROUGH SKIN.

CONTAINS MATERIAL WHICH CAUSES DAMAGE TO THE FOLLOWING ORGANS: KIDNEYS, GASTROINTESTINAL TRACT, RESPIRATORY TRACT, SKIN, CENTRAL NERVOUS SYSTEM, EYE, LENS OR CORNEA.MAY BE HARMFUL TO ENVIRONMENT IF RELEASED IN LARGE AMOUNTS. VERY TOXIC TO AQUATIC ORGANISMS.

WARNING: This product contains a chemical(s) known to the State of California to cause birth defects or other reproductive harm.

The essential operating requirements of the process are maintenance of an interface that is essentially gold, mercury, uncontaminated by either liquid or solid films; and presentation to this interface of precious-metal particles with clean metallic surfaces.

Contamination of the interface occurs in a variety of ways. The most usual cause of contamination is an oil that is or contains a fatty acid or a GREASE.

Most machine and cylinder oils and greases used around mines and mills fall into this category.

Clean, free gold from primary unoxidized ores is bright and clean and, if brought into contact with clean mercury, amalgamates readily and quickly.

Gold from oxidized ores, on the other hand, is almost invariably TARNISHED (lightly filmed with a non-gold-bearing film), and frequently COATED (rusty) with a heavy film in which oxides of iron are an important part.

Tarnished gold does not amalgamate readily; coated gold will not amalgamate at all.

Preparation, in such cases, must be such as will remove the tarnish and coating; mechanical means (grinding) is almost invariably the method employed.

Amalgams are defined as alloys of mercury and other metals.

Considerable evidence is cited (Rose) for the existence of a series of compounds of gold and mercury ranging from AuHg2 to Au8Hg.

Mercury filtered from amalgams contains about 0.14% Au at normal temperatures and 0.65% at 1000 C. these figures are taken to indicate solubility.

Information is from Taggart, and Charles Kubach, Mining and Mineral Process Engineerhttp://mine-engineer.com/mining/minproc/MercAmal.htm

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