Summary of Mercury Amalgamation Gold Extraction Process

1. Mercury Amalgamation Gold Extraction Process Principle

The principle of gold extraction by using mercury (amalgamation method) is mainly that after the mercury is added to the slurry, the surface of the gold particles is wetted by mercury, and then the mercury diffuses into the interior of the gold particles, causing a chemical reaction. Au+2Hg=AuHg2. Finally, the solid of Au3 Hg will form. When the obtained solid matter is heated, the mercury will volatilize into an elemental form, and the gold will exist in the form of sponge gold.

2. Mercury Amalgamation Gold Extraction Process Types

Mercury amalgamation gold extraction process is generally divided into two types, mainly internal mercury amalgamation method and external mercury amalgamation method.

（1）Internal Mercury Amalgamation Gold Extraction Process

Internal mercury amalgamation gold extraction process refers to extracting gold from the inside of the grinding equipment. The extraction of gold is accomplished by adding mercury while the grinding operation is being carried out. The internal mercury amalgamation is mainly used to process ore with high grade, which is one of the commonly used methods for processing gravel mine. The extraction of gold becomes easier when other impurities in the gold ore are low in content, the dissemination size of gold is coarse and there is no sulfide that will pulverize mercury. At this point, the gold can be extracted by internal mercury amalgamation while grinding the ores. The commonly used equipment mainly includes the special small ball mill, mixed mercury barrel, ore pound, and roller and so on.

（2）External Mercury Amalgamation Gold Extraction Process

External mercury amalgamation gold extraction process refers to extracting gold outside of grinding equipment. It is mainly used to extract part of free gold. Especially when the dissemination size of gold is fine, it can use this method for gold extraction. The commonly used equipment generally includes mercury mixing board and mercury mixing machinery of various structures. The mixed mercury plate is usually assembled in ball mill, classifier or bushy machine, which is used to extract monomer native gold pellets. In addition, external mercury amalgamation method and internal mercury amalgamation method can be used in combination, which can extract some gold granules and mercury paste from internal amalgamation equipment, and improve the recovery rate of gold.

3. Mercury Amalgamation Gold Extraction Process Characteristics

(1) Advantages

Simple equipment, small floor space, low investment, energy saving, low production cost, uncomplicated process flow, easy operation and good economic benefits.

The mercury amalgamation gold extraction process has a particularly large enrichment ratio. It can obtain gold amalgam with about 30% grade from raw ore containing 2-3 g/ton of gold, and the gold amalgam can be refined into gold with more than 70% grade in the mine, which greatly reduces the transportation of semi-finished products in mines.

(2) Disadvantages

Mercury is a highly toxic substance, which needs to be handled carefully during use, and the sewage it produces must be strictly controlled. The pollution of mercury to the environment is also the key controlling target of environmental protection departments in various countries over the years. Mercury pollution will spread over large areas with mediums such as atmosphere and water, making it more difficult to control.

4. Mercury Amalgamation Gold Extraction Process Case

The metal minerals in a gold-copper-pyrite mine in China account for 10%-15%, mainly chalcopyrite, pyrite, magnetite, and gangue minerals are mainly quartz and chlorite gneiss.

The average grade of copper raw ore is 0.15-0.20%, the average grade of iron is 4-7%, the average grade of gold is 10-20g/t, and the grade of silver is about 2.8 times that of gold. The plant uses amalgamation method to extract gold, and the total gold recovery rate of the mine is 70%.