The method of the current gold ore amalgamation amalgamation amalgamation inner and outer amalgamation two methods, the amalgamation of the ore is pulverized and mixed with mercury in the Grinding Equipment simultaneously mixing the mercury method. Commonly used internal amalgamation equipment include a rolling mill, a rake mining machine, a mercury mixing cylinder and a special small ball mill , a rod mill and the like. The mercury mixing method in the external amalgam equipment room is carried out outside the grinding equipment. The commonly used external mercury Mixing Equipment mainly includes a mercury-mixing board and a mercury-mixing machine with different structures. When the content of copper , lead and zinc minerals in gold-bearing ore is very small, the ore contains no sulfides for pulverizing mercury. When the size of gold is coarser and the method of gold extraction is the main method of gold extraction, it is generally used for internal mixing. Mercury is gold. The external amalgamation method is only used as an auxiliary means to recover some of the fine-grained gold and mercury paste overflowing from the internal amalgamation equipment such as the radon. Gold mines often use internal amalgamation to separate gold from other heavy minerals. The internal amalgamation equipment is also used to treat re-selected coarse concentrates and other gold-containing intermediates, and the internal amalgamation equipment is ground while mixing mercury to recover gold particles. When the size of the gold is fine, and the flotation or cyanidation method is the main method of gold extraction, the gold is generally extracted by the external amalgam method, and the mixture is mixed in the ball mill grinding cycle, the classifier overflow or the thickener overflow cycle. Mercury plate to recover monomeric natural gold particles. Under these conditions, amalgamation is rarely carried out in a ball mill.
Mercury in the amalgamation tank
First, the re-elected fine sand is fed into the amalgamation cylinder (machine), and an appropriate amount of mercury is injected into the mercury-mixing cylinder. At the same time, water and lime are added for grinding and amalgamation (the amalgamation method is based on gold particles). It is easy to be selectively wetted by mercury, and then the principle of gold amalgam is diffused into the gold particles to collect gold, and finally the gold forms a solid solution mercury paste in the mercury. The monomer in the ore after being crushed and pulverized is dissociated. Gold is immediately included in the mercury solution to form a mercury-gold combination. Mercury is collected every 4 to 10 hours. After the machine is shut down, the sealing cover is opened, and the discharge cover with the boring hole is replaced. The belt is slowly moved by hand to make the discharge opening rotate downward. The soft mercury paste and slurry in the mercury mixing tube flow under the action of gravity and water flow. Collect the water in the bottom of the rack (add a certain amount of mercury to the bottom of the mill when the mercury paste is collected, make the mercury paste soft and easy to collect); use a spoon to pour the slurry in the large pot into the small plastic pot. , turns on the water and continue washing, while stirring the slurry small pots, (since the density of water, 13.6 g of silver cc, density 1.45 g cm ore, a great density difference, in the medium, is much greater than the settling velocity of the mercury amalgam ore, the ore Spill out with water, leaving a pure mercury paste) until the pelvic floor is left with only amalgam. Then apply a mercury paste, put on a rubber glove and add water in the water tray to repeatedly rinse the mercury paste to wash out the impurities until the mercury paste is bright and clean; collect the cleaned soft amalgam and use the dense woven fabric to remove excess mercury. Extrusion to obtain a hard mercury paste; finally, amalgam distillation is performed to obtain a high gold content sponge gold.
Mercury mixing machine
The treatment of amalgam includes three main steps of washing, pressure filtration and distillation. After the mercury paste is treated, sponge gold and mercury are finally obtained. After the sponge gold is smelted, gold and silver alloy ingots can be obtained and sold to a bank or sent to a refinery for refining. The recovered mercury returns to the amalgamation operation.
1. Washing of mercury paste
Mercury paste collected from amalgamation equipment, such as mercury amalgamation, amalgamation chute, thorium mining machine and amalgamation tank, can be sent after washing to remove heavy sand, gangue and other impurities Pressure filtration.
The mercury paste scraped from the mercury-mixed plate is relatively pure and the treatment is relatively simple. Washing is carried out on the console. A thin copper plate is placed on the operation table, and a wooden strip of 20-30 mm is nailed around the table to prevent the mercury which is dispersed during operation from being spilled onto the ground. A hole is drilled in the table, and mercury that flows during operation can flow through the hole to the mercury susceptor. The mercury paste scraped from the mercury plate is repeatedly washed in the porcelain plate and water is added. The operator puts on the rubber glove and continuously rubs the mercury paste with his hand to wash the impurities in the mercury paste to the utmost extent. Mixed amalgam in the scrap iron magnet can be used to suck out. In order to make the mercury paste soft and easy to wash, it can be diluted with mercury. Washing the mercury paste with hot water can also make the mercury paste soft and easy to wash, but it will accelerate the evaporation of mercury and endanger health. It is not advisable to use hot water to wash the mercury paste if the safety measures are not available. The mercury paste with high impurity content is dark gray. The washing operation should wash the mercury paste until it is bright and smooth, then wrap the mercury paste with a dense cloth and send it to the pressure filter.
Mercury pastes obtained from amalgamation cartridges and mercury traps contain large amounts of impurities such as heavy sand minerals and gangues, usually separated by short chutes or gold pans to separate the mercury paste from other heavy minerals. Mercury pastes produced in various mechanical washing and mixing amalgamation tubes, such as amalgamation plates and small cyclones, are more commonly used abroad. Figure 1 is a structural diagram of a sharp-bottom gold pan used in many gold mines in South Africa. The disc has a diameter of 900-1200 mm, the bottom of the disc is concave, and the circumference of the disc is 100 mm high. The rear of the disc is connected to the crank rod, and the front end of the disc is supported by the scroll. On the guide roller, through the bevel gear transmission, the disc is horizontally moved by the crank mechanism, and the mercury paste produced by the mercury-mixing cylinder is placed in the disc, and the mercury paste is applied due to the rotary motion of the disc and the flushing of the water flow. The gangue entrained in the middle is sent to the front end of the disc to be discharged through the chute, and the mercury paste having a large density (specific gravity) is collected in the center of the disc and discharged through the discharge port. Each 1200mm diameter tipping gold pan can handle 2-4t amalgamation cylinder products daily.
The structure of the heavy sand separation disc developed in China is similar to that of the sharp bottom gold pan. The diameter of the disc is 700mm, the height is 120mm, the working time is 1.5-2.0h, and the product of 60-120kg amalgamation can be processed at one time.
There is also a mercury paste separator in foreign countries. The structure is shown in Figure 2. The separated material is sent to the receiving hopper, and the coarse-grained gangue is removed through the screen. The fine-grained material passing through the screen falls into the front-end trap. Box, in this box, the material is flushed with water, so that the fine-grained gangue particles enter the terminal trap box through the stage grid, and the mercury paste is left in the front-end trap box and the grid, and is cleaned up by mechanical equipment. The amalgam is sent for washing, and the washing method is the same as the method of washing the mercury amalgam.
2. Pressure filtration of mercury paste
The washed mercury paste still contains a large amount of excess mercury, ie free mercury, which can be removed by pressure filtration. The washed amalgam is sent to a pressure filter with a dense canvas to remove excess mercury and to obtain a concentrated solid mercury paste (hard mercury paste). In small-scale production, manual pressure filtration is also used, and it can also be squeezed by a screw filter press or a lever filter press. Plants with large amounts of mercury paste work with pneumatic and hydraulic filter presses.
The structure of the screw filter press commonly used in gold mines is shown in Figure 3. The chassis is drilled with holes and can be removed. During operation, the wrapped mercury paste is placed on the chassis and fixed firmly with the cylinder. The hand wheel is rotated to push the screw to push the piston down to squeeze the mercury paste. The excess mercury in the mercury paste is extruded through the circular hole in the chassis. It flows out and collects in a container at the lower part of the filter press. The hard mercury paste can be removed by removing the chassis.
The solid mercury paste produced by pressure filtration contains 20%~50% of gold, and its gold content mainly depends on the size of the amalgamated gold particles. When the gold particles are larger, the gold content is as high as 45% to 50%, and the gold content is reduced to 20% to 25%. In addition, the gold content of the hard amalgam is also related to the pressure of the filter press and the density of the filter cloth.
Mercury recovered by mercury paste filtration often contains 0.1% to 0.2% gold and can be returned for amalgamation. The gold recovery capacity of recovered mercury is higher than that of pure mercury. Especially when the mercury amalgamation plate fails, it is better to use the mercury recovered by mercury paste pressure filtration. When the mercury-mixed gold particles are extremely fine and the filter cloth is not dense, the gold content in the recovered mercury is high, so that after the mercury is recovered for a long time, the gold will precipitate and sink to the bottom of the container.
3. Distillation of mercury paste
The pressure-filtered amalgam still contains a considerable amount of mercury, some of which form a solid solution or compound with gold, and the other part is free mercury that has not been filtered by pressure filtration. Generally, the mercury content is 20% to 50%. The separation of mercury from gold in a solid mercury paste is achieved by distillation by means of a large difference between the vaporization temperature of mercury (356 ° C) and the melting point of gold (1063 ° C). In order to vaporize mercury in the mercury paste, it is not only possible to heat it to the boiling point of mercury (356 ° C), because this temperature can only vaporize free mercury; and those compounds and solid solutions of mercury and gold have not yet been decomposed. In order to completely decompose the compound, it is necessary to heat to 420 ° C; in order to decompose the solid solution, it is heated to about 800 ° C.
The solid mercury paste produced by the gold plant can be distilled periodically. The solid mercury paste is placed in a sealed cast iron can (pot) during operation, and the top of the can is connected to an iron tube equipped with a condensing tube. The tin (pan) is placed heating furnace coke, coal gas or electric heating, when the temperature is slowly increased to 356 deg.] C, i.e. mercury amalgam vaporized and escape along the iron pipe, condensed and spherical droplets Recycled in a container filled with water. In order to fully separate the mercury in the mercury paste, many gold-selecting plants control the temperature of the steamed mercury to 400-450 ° C, and the temperature of the late-stage steaming to 750-800 ° C, and keep it for 30 min. The time for steaming mercury is about 5~6h or longer, and the recovery rate of mercury in steaming operation is usually more than 99%.
The size of the distillation equipment depends on the scale of production. Most small mines use distillation tanks, while large mines use distillation furnaces. The structure of the small distillation tank is shown in Figure 4, and its technical specifications are listed in the table below.
The distillation operation is to put the mercury paste into the iron can, and after heating the sealing cover, gradually heat it to 400 ° C (generally heating for 2 to 4 hours), then the free mercury escapes; continue to heat up to 800 ~ 850 ° C, at this temperature Hold for half an hour to fully evaporate the mercury and completely decompose the mercury gold compound. At the end of the distillation, the residual amount of mercury in the gold does not exceed 0.1%. Mercury vapor is cooled along the condenser into cold water and recovered. The mercury recovered by distillation is filtered to remove impurities entrained in the machine, and then treated with 5% to 10% of dilute nitric acid (or hydrochloric acid) to dissolve the base metal contained in the mercury, and then returned to the amalgam operation for reuse.
The sponge produced by distillation has a gold content of 60% to 80% (sometimes as high as 80% to 90%), and contains a small amount of mercury, silver, copper and other metals. Melting impurities contained in the next step, is removed by a solvent (such as soda, borax, saltpeter) oxide slagging. Generally, graphite crucible is used to melt into a combined gold in a diesel or coke oven. If the content of gold and silver in sponge gold is low, and the content of impurities such as silica and iron is high, sodium sulphate and a small amount of sodium nitrate and borax may be added during smelting to oxidize and slag, and a large amount of impurities are removed, and then fused gold is cast. . In large gold mines, sponge gold can also be smelted in a converter or an electric furnace. When the content of impurities in the sponge gold is high, it is also possible to remove a large amount of impurities by acid leaching, alkali leaching, etc. before melting the ingot. Sponge gold with a total amount of gold and silver of 70% to 80% can be cast into an alloy plate for electrolysis purification.
The following points should be noted when distilling solid mercury paste in a distillation tank:
â‘ before canning amalgam should be pre-coated with a distillation tank wall St. pasty white powder or graphite powder, talc, iron oxide powder, to prevent post-distillation gold particles adhered to the wall of the tank.
2 The thickness of the mercury paste in the distillation tank is generally 40~50mm. If the thickness is too large, the mercury distillation will be incomplete, and the distillation heating time will be prolonged. When the mercury paste is boiling, the gold particles are easily sprayed to the outside of the tank.
3 Mercury paste must be pure, can not be mixed into the packaging paper, otherwise, mercury recycling will occur when mercury is recycled. When the mercury paste is mixed with heavy minerals and a large amount of sulfur, the bottom of the tank is easily perforated, resulting in loss of gold.
4 Since the decomposition temperature of AuHg2 (310 ° C) is very close to the vaporization temperature of mercury (356 ° C), the temperature should be slowly increased when the mercury is evaporated. If the sharp rise in the furnace, AuHg2 that is still in the decomposition of mercury into the sublimation stage, could easily lead to mercury fierce boiling and splashing phenomenon. After distilling most of the mercury escapes, the furnace temperature can be increased to 750 ~ 800 ℃ (due to a decomposition temperature of 402 Au2Hg deg.] C, the decomposition temperature is 420. Au3Hg deg.] C), and incubated 30min, so as to completely discharge the residual mercury in the tank .
⑤ deriving iron pipe end retorts should maintain a certain distance from the surface of the water collection basin cooled mercury to prevent mercury vapor during the late negative pressure inside the tank, and the water condensed mercury is sucked back into the tank explosion.
â‘¥ steam mercury should maintain good ventilation to avoid the escape of mercury vapor endanger the health of workers.
Large gold mines can use distilled furnaces to steam mercury, and there are many types of distillation furnaces. Figure 5 shows one of them. The distillation cylinder of the furnace is cylindrical, with a diameter of 225~300mm and a length of 900~1200mm. The front end of the distillation cylinder has a sealed door, and the other end is connected with the lead-out iron pipe. The iron pipe has a cooling water jacket. The mercury paste is placed in a tin box covered with a porous iron sheet, and the iron box is placed in a distillation tank. Fig. 6 is a structural view of an electric furnace for distilling a mercury paste.
Frequently encountered problems with amalgamation
In order to improve the recovery of gold amalgamation of the need to strengthen the operation management of mercury plate. The main operational factors affecting the effect of mercury amalgamation are the ore size, ore concentration, slurry flow rate, mineral acidity and alkalinity, the additional time and amount of mercury added, the time of scraping the mercury paste, and the prevention of mercury plate failure. It is summarized as follows:
1 feed size. The suitable ore size of the mercury plate is 3.0-0.42 mm. When the particle size is too coarse, not only the gold particles are difficult to dissociate, but also the coarse ore particles easily rub the surface of the mercury plate, causing the loss of mercury and mercury paste. For ore containing fine gold, the ore size can be as small as about 0.15 mm.
2 feed concentration. The concentration of the mercury plate is 10%-25%, and the concentration of the slurry is too large, so that the fine gold, especially the tiny gold piece which becomes the ship type during the grinding process, is difficult to settle to the mercury plate. Too small a feed concentration will reduce the mercury plate productivity. However, in the production practice, the concentration of the slurry of the mercury plate is often determined by the concentration of the slurry in the subsequent operation, so sometimes the concentration of the mercury plate is as high as 50%.
3 slurry flow rate. The slurry flow rate on the mercury plate is generally 0.5-0.7 m/s. When the ore amount is fixed, the slurry flow rate is increased, the thickness of the slurry layer on the mercury plate is thinned, and the heavy metal sulfide is easily deposited on the mercury plate, which deteriorates the amalgamation operation condition, and the flow rate is too large, which also reduces the gold recovery rate.
4 mineral acidity and alkalinity. Mercury in an acidic medium can clean the surface of mercury and gold particles and improve the wetting ability of mercury to gold. However, the slime is not easy to aggregate and contaminate the surface of gold particles, which affects the wetting of gold by mercury. Therefore, the amalgamation operation is generally carried out in an alkaline medium having a pH of from 8 to 8.5.
5 additional time and additional amount of mercury. After the mercury plate is put into production, the initial mercury addition amount is 15-30g/m2. After 6-12h operation, the mercury is added. The amount of each supplement is in principle 2-5 times of the gold content per ton of ore. Usually add 2-4 times a day. Recently, it has been found that increasing the number of mercury additions can increase the recovery rate of gold. For example, the number of mercury additions in a gold mine in the former Soviet Union has increased from twice a day to six times a day, and the recovery rate of mercury amalgamation work can be increased by 18%-30%. China's production practice shows that the additional time of mercury and the amount of mercury added should maintain a sufficient amount of mercury throughout the amalgamation cycle, and amalgamation can be performed throughout the process of slurry flow through the amalgam plate. Excessive amounts of mercury will reduce the elasticity and consistency of the mercury paste, which will easily lead to the loss of mercury paste and mercury with the slurry; the amount of mercury is insufficient, the mercury paste is hard, loses its elasticity, and the ability to capture gold decreases.
6 shaving the paste time. Generally, the time of amalgam scraping is consistent with the time of supplemental mercury. In order to facilitate management, gold mines in China generally scrape mercury paste once per job. When scraping the mercury paste, stop the ore, rinse the mercury plate, and scrape the mercury paste from the lower part of the mercury plate with a hard rubber plate. Some foreign mines heat the mercury plate before scraping the mercury paste, making the mercury paste soft and easy to scrape. In some mines in China, some mercury is sprinkled onto the mercury plate before the mercury paste is applied, which can also make the mercury paste soft. Practice has shown that the amalgam scraping is not necessarily thorough, and it is beneficial to leave a thin layer of mercury paste on the mercury board to prevent the mercury board from malfunctioning.
7 mercury plate failure. Mercury plate failure due to improper operation can cause the mercury plate to reduce or lose the ability to capture gold. This phenomenon is called mercury plate failure. Its manifestations are mainly mercury plate dry, mercury paste hard, mercury micronization, mercury powdering and oil pollution. The causes and main preventive measures for mercury plate failure are:
The mercury plate is dry and the mercury paste is hard: often because the amount of mercury added is insufficient, the mercury paste is in a solid solution state, causing the mercury plate to dry up and the mercury paste to be hard. Regular inspections and timely addition of appropriate amounts of mercury can eliminate this phenomenon.
Mercury micronization: Mercury micronization sometimes occurs when mercury is recovered by distillation. At this time, mercury can not be spread evenly on the mercury plate. Mercury is easily taken away by the slurry flow, which not only reduces the gold capture ability of mercury, but also causes the loss of gold. When using mercury recovery, the state of mercury should be checked before use. In the case of micronization, the sodium metal can be carefully added to the mercury before use to restore the agglomerated mercury.
Mercury pulverization: The action of sulfur and sulphide in the ore and mercury can cause mercury to pulverize and form black spots on the mercury plate, which causes the mercury plate to lose its ability to capture gold. When a sulfide ore containing arsenic, antimony, bismuth, this phenomenon is particularly remarkable. Oxygen in the slurry oxidizes the mercury and creates red or yellow-red spots on the mercury plate. Commonly used chemicals abroad to eliminate such failures. Gold mines in China often use the following methods to eliminate mercury powder failure: a) increase the amount of lime, increase the pH of the slurry to inhibit the activity of sulfides; b) increase the amount of mercury added, so that the powdered mercury is lost with excess mercury; c) increase the pulp When the flow rate causes the ore particles to wipe off the marks on the mercury plate and the polymetallic sulfide in the ore, the phenomenon that the polymetallic sulfide adheres to the mercury plate to deteriorate the mercury amalgamation often occurs. At this time, the amount of lime is increased and the pH of the slurry is increased. (Sometimes up to 12 or more) to remove copper ions and grease, and to add lead salts to remove sulfur ions, can reduce or eliminate the adverse effects of polymetallic sulfides.
Oil pollution: The oil mixed into the slurry will deteriorate the amalgamation process and even interrupt the amalgamation process. Special care should be taken during operation so that oil is not mixed into the slurry.
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