Mercury mixing process (3)
3 mercury plate production. Production of mercury plate may be a copper plate purple, silver and silver-plated copper plate three materials.
Production practice shows that the silver-plated copper plate has the highest mercury-mixing efficiency, and the gold recovery rate is 3%-5% higher than that of the copper plate. Although the silver-plated copper plate adds a silver plating process, it has a series of advantages, such as avoiding the formation of colored copper oxide film and its derivatives, which can reduce the surface tension of mercury, thereby improving the wettability of mercury to gold. At the same time, due to the pre-formation of silver amalgam, the surface of the mercury plate has great elasticity and wear resistance. The silver amalgam has greater resistance to the interference of the acid and sulfide in the slurry than the simple mercury. Therefore, silver plated copper plates are commonly used in the industry as mercury plates. Although the use of a copper plate as a mercury plate can eliminate the silver plating process, the price is lower than that of the silver plated copper plate, but it needs to be annealed before use to make the surface loose and rough, and the gold-harvesting effect is worse than that of the silver-plated copper plate. The sterling silver plate does not need to be silver plated, but it is expensive, the surface is smooth, the amount of mercury is insufficient, and the gold-harvesting effect is worse than that of the silver-plated copper plate.
The production of silver-plated copper plate includes three steps of shaping the copper plate, preparing the plating solution and electroplating:
a) Copper plate shaping: Cut the 3-5mm thick electrolytic copper plate into the desired shape, remove the surface oil stain by chemical method or heating method, flatten with hibiscus, remove burrs, marks and polish with wire brush and fine sandpaper. Post-plating.
b) Preparation of plating solution: The plating solution is a silver potassium cyanide aqueous solution. The composition of 100 L electroplating solution is: 5 kg of electrolytic silver, 12 kg of potassium cyanide (purity of 98%-99%), 9-11 kg of nitric acid (purity of 90%), 8-9 kg of salt, and 100 L of distilled water. The basic reaction when preparing the electrolyte is:
2Ag+4HNO 3 →2AgNO 3 +2H 2 O+2NO 2
AgNO 3 +NaCl→AgCl+NaNO 3
AgCl+2KCN→Ag(CN) 2 +KCI
The preparation method comprises dissolving electrolytic silver in dilute nitric acid (electrolytic silver: nitric acid: water = 1:1.5:0.5), heating to 100 ° C, and evaporating to obtain silver nitrate crystal; dissolving silver nitrate in water and adding it under stirring Saline solution until no white precipitate appears in the liquid, then wash the precipitate to neutral; dissolve potassium cyanide in water, add human silver chloride to make silver plating 50g / L, cyanide 70g / L plating liquid.
c) Silver plating of copper plate: The plating tank can be made of wood, ceramic, cement or plastic plate, and is rectangular, and its volume is determined by the size and quantity of silver-plated copper plate. The mercury plate of a gold mine in China is 1.2m long and 0.5m wide. It uses a wooden plating tank with a length of 1.6m, a width of 0.5m and a height of 0.6m.
When electroplating, the electrolytic silver plate is used as the anode, the copper plate is used as the cathode, the electrolytic cell is pressed 6-l0v, the current density is 1-3 A/cm 2 , the plating temperature is 16-20 ° C, and the thickness of the silver plating on the copper plate should be 10-15 μm. .
2) Operation of amalgamation plate In the gold selection process, the mercury-mixing plate is mainly set in the grinding and grading cycle, and the coarse-grained free gold is directly recovered from the ball mill discharge. At this time, the recovery rate of the mercury-mixing operation gold is high, and some mines have a high recovery rate. Up to 60%-70%. A gold mine in China has captured 1.5-2.0mm coarse gold on the mercury plate, indicating that this formulation is reasonable. Some mines use mercury plates outside the grinding and classification cycle to recover free gold from the cascade overflow. Practice has shown that the recovery rate of this formulated amalgamation work gold is low, and some mines only reach 30%-45%. [next]
In order to increase the recovery rate of gold during amalgamation, it is necessary to strengthen the operation management of mercury plates. 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 amount of mercury added is 15-30g/m 2 . After 6-12 hours of 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. [next]
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 grease and copper ions, to remove sulfur plus lead salt ions can reduce or eliminate adverse effects of sulphides.
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.
3) Feeding the tank and the mercury trap The front end of the mercury amalgamation plate is set to the mine tank (slurry distributor), and the mercury trap is installed at the end.
The ore box (slurry distributor) is a rectangular wooden box, and a plurality of small holes having a diameter of 30-50 mm are opened on the side of the mercury plate so that the slurry flowing out of the hole is covered with the mercury plate, generally before each small hole The nail has a movable diamond-shaped block, and the direction of the block is adjusted to make the slurry evenly cover the surface of the mercury plate.
The mercury trap is installed at the end of the mercury plate to capture mercury and mercury paste that is lost with the slurry. The pulp is decelerated in the mercury trap, and the difference in density (specific gravity) is used to separate the mercury and the mercury paste from the gangue. There are many types of mercury traps, the simplest of which is shown in Figure 7.
The tank is equipped with a partition. The slurry flows into the tank from the mixed mercury plate, and is discharged from the overflow through the gap under the partition. The mercury and mercury paste deposited on the bottom of the tank are periodically removed. Generally, the ascending flow rate of the slurry in the mercury trap is 30-60mm/s, when the material density (specific gravity) is large and the particle size is coarse, in order to improve the mercury capture effect, a hydraulic mercury trap is often used. There are various types. Figure 8 shows a kind of hydraulic mercury trap. Water is added from the lower part of the mercury trap to cause pulsating water flow. The frequency is 150-200Vmin, which can improve the stratification of mercury and mercury paste and gangue. And separation effect.
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4) In addition to the commonly used mercury-mixing plates, other mercury-mixing machines also have short-cone hydrocyclone for fine gold-grain mixed mercury, and mercury plates are laid on chutes and shakers. In addition, some new models have been developed at home and abroad in recent years. Mercury amalgamation equipment, which mainly has the following types:
1 swirling amalgamator. It is made according to the principle of hydrocyclone. It is used in the second section of the grinding circuit in the gold mines of the United States and South Africa. The slurry is pressed into the mercury-adding equipment and rotated in the tangential direction. The pulp and mercury are subjected to strong agitation and are constantly moving. It promotes the contact of gold particles with mercury to achieve amalgamation, thus enhancing the amalgamation operation and increasing the recovery rate of gold.
2 continuous amalgamator. The continuous swirling amalgam mixer developed by the United States, the slurry is fed by the feed pipe, and under the action of water, it is swirled and mixed with mercury. The mercury can be recycled, and the mercury paste is periodically discharged. The slurry after the mercury is lifted by the siphon and discharged from the mine. The tube is discharged and can be continuously operated. In the process of swirling amalgamation, the surface of the gold particles is subjected to friction, which can improve the efficiency of mercury mixing.
The centrifugal continuous amalgamator developed in China is shown in Figure 9. The principle is similar to that of a continuous amalgamator. The slurry is fed into the mercury bed in the amalgamator. The water pressure of the centrifugal circulating water pump causes the ore to rotate on the bed surface. The centrifugal force separates the ore sand, and the gold particles with large density (specific gravity) sink on the mercury bed surface and sweep the mercury layer for mercury amalgamation. The heavy sand, water and mercury in the slurry after the mercury amalgamation enter the siphon through the bell mouth. When the slurry enters the spherical chamber, it suddenly decelerates. The mercury flows back under the action of gravity. The water and heavy sand continue to rise into the separator and finally exit from the overflow. The resulting mercury paste is larger than the density (specific gravity) of the newly added mercury, sinking at the bottom of the mercury bed and can be periodically discharged.
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3 electrical amalgamation machinery. Foreign countries have made amalgamation equipment such as electric amalgamation board, electrolyzed centrifugal amalgamation machine, electric gold selection hopper, etc., which have the common point of connecting the cathode of the circuit to the surface of mercury to polarize the surface of mercury to reduce the surface tension of mercury. The oxygen film deposited on the surface of the cathode reduces the oxide film on the surface of the mercury to activate the wettability of the mercury. Therefore, electrical amalgamation can increase the efficiency of mercury mixing. At the same time, electrical amalgam can use a more active amalgam containing a small amount of other metals (such as zinc amalgam, sodium amalgam) instead of pure mercury, which helps to improve gold recovery.
Practice has proved that the effect of amalgamation is mainly the width of the mercury plate, not the length. Because when the flow rate of the slurry is constant, the mercury plate is wider, the slurry layer can be thinned and evenly distributed, which is favorable for the gold particles to contact with the mercury plate. Since most of the gold particles are amalgamated in front of the mercury plate, it is meaningless that the mercury plate is too long. When the mercury amalgamation board is used as an auxiliary facility for internal amalgamation to capture the lost mercury paste and mercury, the length of the mercury plate is generally 5-6 m; if only the coarse gold particles are collected, the amalgamation plate can be set in the grinding classification closed circuit. In the cycle, the length is 2-4m. The slope of the mercury plate is related to the ore size and slurry concentration. When the ore is coarser and the slurry is thicker, the inclination should be larger; otherwise, it should be smaller.
The upper end of the mercury amalgamation plate is usually provided with a feed tank, and a mercury trap is installed at the end. The feeding tank is used to evenly distribute the slurry supplied to the mercury-mixing plate on the entire surface of the board. It is a rectangular water tank with a number of small holes 30-50 mm in diameter facing the side of the mercury plate, and the slurry flows out through the small holes. Covered with mercury plates. Mercury traps are used to capture mercury and mercury pastes that are lost from the slurry on the mercury plate. The working principle is based on the difference in specific gravity and sedimentation velocity of mercury or mercury paste and gangue at a slow flow rate. To make mercury and mercury paste sink and gangue flow to achieve the purpose of collecting mercury and mercury paste.
Select suitable operating conditions to ensure a high recovery rate of mercury amalgamation, suitable ore feeding size is 0.42-0.30mm; ore concentration is preferably 10%-25%, but if the mercury plate is in flotation or cyanide Before the use of large gold, it can increase the concentration of ore, sometimes up to 40%-50%; the slurry flow rate on the amalgamation board is generally 0.5-0.7m/s; the amalgamation operation is carried out in an alkaline medium. The pH of the slurry is usually adjusted with lime, and the optimum pH is 8.0-8.5.
The amount of mercury added should be appropriate. Adding too much mercury will reduce the elasticity and consistency of the mercury paste, and it will easily cause the mercury paste and mercury to be lost with the slurry. If the amount of mercury is insufficient, the mercury paste is hard and the ability to capture gold is reduced. When the mercury plate starts to mix mercury, the first amount of mercury is 15-30g/m 2 , and the mercury is added every 6-12h. The amount of mercury added is generally 2-5 times of the gold content of the ore. The amount of mercury consumed by 1t ore is 2-9g. When processing ore containing arsenic and antimony, the mercury consumption is 10-15g.
The time to scrape the mercury paste is consistent with the time to add mercury. Some mines are easy to manage, and it is required to scrape the mercury paste once per shift (8h). When scraping the mercury paste, stop the feeding. First, rinse the mercury plate and scrape it from the lower part of the mercury plate with a hard rubber plate. It is not necessary to completely scrape off the mercury paste. A thin layer of mercury paste on the mercury plate is good for amalgamation and prevents the mercury plate from "getting sick". Mercury plate "illness" will result in reduced or lost gold capture capacity. The main symptoms are: the mercury plate is dry, the mercury paste is hard, indicating that mercury should be added immediately; the mercury on the mercury plate is powdered, which can increase the amount of mercury added, so that the powdered mercury flows away with excess mercury. , or increase the amount of lime to increase the pH of the pulp; the mercury plate produces various color spots (the most common is copper hydroxide green spots and black spots caused by the decomposition of sulfides), which can be eliminated by increasing the amount of lime ( Sometimes the pH needs to be as high as 12 or more, or chemical treatment (such as green spot can be washed with 2% cyanide solution, after removing the marks, brush a thick layer of silver mercury paste with the brush to the original green spot). The method of preparing the silver amalgam is as follows: adding 16 g of mercury per gram of metallic silver, adding metal mercury to the 10%-15% AgNO3 solution, dissolving and extruding the liquid with buckskin or canvas to obtain a paste silver Mercury paste. If the copper plate is coated with a silver mercury paste as a mercury amalgam plate, the surface of each square meter consumes 300-600 g of silver.
The dark spots were scrubbed with a mixture of 4 liters of water plus 5 kg of ammonium chloride, 1.7 kg of slaked lime, and 0.25 kg of sodium carbonate. Once the black spots are produced, they should be removed immediately, otherwise they will be difficult to remove. When oil stains appear on the board surface, it should be washed with 2%-3% caustic soda solution.
Vibrating amalgam plates are currently only used abroad. The utility model is characterized in that the bed surface is driven by the transmission mechanism to oscillate laterally, thereby increasing the contact chance of the gold particles and the mercury liquid on the surface of the mercury plate, and strengthening the mercury mixing operation process. This equipment is suitable for processing fine-grained gold mines.
Other external amalgamation machines, some in order to strengthen the amalgamation operation, set agitation devices in the amalgamation equipment to increase the contact opportunities between the mercury and the ore; some are to make the amalgamation operation continuous; some are to introduce high-voltage current in the amalgamation equipment, Promote the infiltration of mercury into the gold particles; some are to achieve mechanization and automation of the amalgamation operation.
The external amalgamation operation generally recovers the coarse gold particles in the slurry from the ball mill. In the operation, the time of adding mercury and the amount of mercury, the size of the ore, the concentration of the ore, the flow rate of the slurry, the pH of the slurry, the time of the paste, and other precautions should be mastered.
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