1. The concept and principle of amalgamation
When liquid mercury and gold particles are in contact, the chemical reaction occurs quickly, producing three compounds of AU2Hg, AUHg, AU3Hg and a solid solution of gold and mercury, so that the mercury spreads on the surface of the gold particles and then diffuses into the gold particles to form mercury. paste. The process of forming a mercury paste is called a homogenization process. The process or method of using mercury to spread rapidly on the surface of gold particles and capturing the characteristics of gold particles to separate monomer free gold from gold ore is called amalgamation.
The amalgamation method is divided into an internal amalgamation method and an external amalgamation method. In the same equipment (mill, ball mill, etc.), the method of collecting and grinding at the same time is called the internal amalgamation method, and the method of amalgamation outside the grinding machine is called the external amalgam method.
2, amalgamation equipment
2.1, external amalgamation equipment
The external amalgamation method is often used as an auxiliary operation before flotation or cyanidation. The external amalgamation equipment is placed between the grinding machine and the classifier to pre-extract the coarse gold particles in the ore.
At present, the external amalgamators commonly used in China are fixed amalgam plates, which are mainly composed of three parts: bracket, bed surface and mercury plate. Multi mercury plate made of silver-plated copper plate, a copper thickness of 3 ~ 5mm, width of 400 ~ 600mm, 600 ~ 1000mm long.
The determination of the area of ​​mercury plate is mainly based on the amount of ore treated, the nature of the ore and the role of amalgamation in the gold extraction process. In the normal amalgamation operation, the thickness of the slurry flow on the surface of the mercury plate is 5~8mm, the flow rate is 0.5~0.7m/s, and the area of ​​the mercury plate required to treat the ore t/d is 0.05~0.1m2, or the area of ​​the unit mercury plate. The processing capacity is 10~20t/dm2. If the purpose of amalgamation is to capture coarse gold, the processing capacity per unit area is increased by 5~10 t/dm2. Practice has proved that the effect of mercury amalgamation depends on the width of the mercury plate, not the length. The reason is that the wider the mercury plate, the thinner the slurry flow and the even distribution, which is beneficial to the contact between the gold particles and the mercury plate.
The inclination angle of the mercury amalgamation plate is related to the ore size and the slurry concentration. The ore particles are coarse, the concentration is high, and the inclination angle should be larger. On the contrary, it should be smaller.
2.2. Operation methods and precautions for external amalgamation operations
In the operation of external amalgamation, it is necessary to master the ore size, feed concentration, slurry flow rate, mineral acidity and alkalinity, addition of mercury, scraping of mercury paste, and prevention and treatment of "sickness" of mercury plate.
Feeding ore, the size of the amalgamation plate should not be too large, too thick and easy to rub the mercury plate, resulting in the loss of mercury and mercury paste, the particle size should be less than 3mm, the concentration should be 20~30%.
The pH and the amalgamation operation generally control the slurry pH value in an alkaline medium of 8 to 8.5.
When mercury is added and the mercury plate is put into production, the initial mercury removal amount is 15~30g/m2, and mercury is added after 6~12h. The amount of addition is in principle 2~5 times of the gold content of each ore.
After scraping the mercury paste, the mercury paste should be scraped after a period of operation. Generally, the mercury paste is scraped in each operation. When scraping mercury, the ore should be stopped, and the slurry on the mercury board should be flushed out and scraped with a hard rubber sheet. It should not be scraped very cleanly, which can enhance the ability to continue the mixing of mercury.
The prevention and treatment of "sickness" of mercury plate, the so-called "illness" refers to the phenomenon that the mercury plate has the ability to reduce the gold-harvesting capacity until it is lost due to the occurrence of stains or other causes on the mercury plate. There are two reasons for this: one is the action of sulfide and mercury. powdered mercury, mercury plate attached to the metal sulfide, mercury capture metal plate becomes ability, especially impact sulfide containing arsenic, antimony, bismuth, and even more simple way to eliminate this effect is to increase the amount of lime The PH value reaches 12 or above; the second is the role of the oxidant in the slurry, which causes the mercury plate to form red or yellow-red spots, and the effect can be eliminated by increasing the amount of lime.
3, the treatment of mercury paste
The treatment of amalgam includes three steps of washing, pressure filtration, distillation, mercury paste treatment, obtaining sponge gold and recovering mercury. Sponge gold can be sold after being roasted.
Washing is to clean the amalgam.
Pressure filtration is to separate excess mercury and obtain a concentrated gold mercury paste.
Distillation is to remove 20-50% of the mercury contained in the mercury paste after pressure filtration by distillation. The following points should be noted when distilling in a distillation tank: First, pre-filling the inner wall of the tank before loading the mercury paste coated with a slurry of graphite powder or chalk powder, talc powder, to prevent the adhesion of gold particles and the tank wall; second, loaded amalgam should not be too thick; Third, be warmed slowly, easily lead to excessive heating of mercury intense Boiling and splashing. When most of the mercury escapes, the furnace temperature can be raised to 750 ~ 8000C, and the distillation was continued at this temperature for 30 minutes in order to completely discharge the residual mercury; Fourth, the lead end of the iron pipe retorts and not collecting the condensed lower Mercury in the basin cooling water phase contact, in case of negative pressure in the tank at the end of distillation, the inverted suction tank will explode; fifth, the distillation site should be well ventilated to prevent mercury vapor from endangering human health.
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