Gold and silver ore dressing (1)

First, the development of domestic mineral veins gold gold ore veins many types, can be summarized as: gold or gold-bearing quartz veins quartz veins type iron ore; gold sodium altered granite type iron ore; metal-containing sulfide ores England jinxin Pulse type, gold-containing oxidized ore quartz vein type and gold-containing tungsten- arsenic ore quartz vein type five. According to the characteristics of each type of ore, one or more comprehensive processes such as re-election, mixing, flotation, cyanide, thiourea, carbon slurry and resin adsorption are used for sorting, sometimes supplemented with water. Metallurgy, heat treatment, etc.
(1) Re-election of the method of re-election is one of the oldest and most popular methods of gold selection. In the gold deposits, gold is usually in the form of monomeric natural gold. The density is generally greater than 16 tons/ ^m3 , which is much different from the density of gangue. Therefore, re-election is the most important, most effective and economical method for selecting gold deposits. Methods. However, in the pulse gold selection plant, the re-election is rarely used alone, and what is part of the joint gold withdrawal process. In the grinding and grading circuit, the jig or spiral chute is used in conjunction with the shaker to recover in advance. Dissociated coarse-grained monomer gold for subsequent flotation or cyanidation operations, and may be qualified gold concentrate. This method is more commonly used in small-scale gold mines and local-group mining mountains, such as Jinchanggouliang and Dashuiqing in Inner Mongolia.
The main equipment for re-election is the various types of chutes, jigs and shakers. In addition to conventional re-election equipment , according to the production characteristics of China's gold mines, based on the digestion and absorption of foreign advanced equipment, China has developed new re-election equipment such as belt slip, Ross chute, round jig, sand gold centrifugal washing unit. Has achieved good results in gold production. For example, Shandong Jinnan Gold Mine Gold Plant has set a soft coating (blanket) chute in the grinding and grading circuit, and the recovery rate of gold can reach 70%. Soft-faced chutes are also used to treat flotation or amalgam tailings to increase gold recovery.
(2) Mercury amalgamation method The mercury amalgamation method can be divided into internal mixed mercury and externally mixed mercury according to its production mode. Gold and heavy sand minerals are separated by common amalgamation method in the sand gold sand mountain; in the vein gold mine, amalgam is usually used as part of the joint process with flotation, re-election, cyanidation, etc., mainly for collecting coarse grain singles. Body gold.
The internal amalgamation is carried out in a mercury amalgamation tank or a grinding machine, which can better control the pollution of mercury.
The main equipment for external amalgamation is a mercury-mixing plate, which consists of a bracket, a bed surface and a mercury plate. Mercury board material purple copper plates, silver plated copper, silver plate, silver-plated copper plate amalgamation best. In order to facilitate silver plating and easy replacement in production, the electrolytic copper plate is often cut into small pieces of 400-600 mm in width and 800-1200 mm in length, and after silver plating, the blocks are laid on the bed surface in the oblique direction of the bracket.
The determination of the area of ​​the mercury plate is related to the treatment of the amount of ore, the nature of the ore and the role of the amalgamation process in the gold selection process. Generally, the mercury plate area required for the treatment of 1 ton of ore is 0.05-0.5 m ² /ton•day on the surface of the mercury plate with a slurry depth of 5 to 8 mm and a flow rate of 0.5 to 0.7 m/s. If the amalgam is only for the collection of large particles of free gold, and the tailings still need to be flotation, re-election or cyanidation, the mercury plate quota can be set at 0.1~0.2 m2/ton•day. The mercury plate quotas under various conditions are listed in Table 1.

The conditions of amalgamation are: the concentration of the ore is 10~25%, the grain size of the ore is 3~0.4mm, and the speed of the ore is 0.5~0.7m/s. The mercury consumption is 3~8g/ton.
Mercury protection: Mercury can be infiltrated into the body in the form of liquids, salts and vapors of the skin, mucous membranes or respiratory tract. Swimming in the kidney, liver, brain, lungs, bones and other organs to poison people. In particular, mercury vapor is the most harmful to humans and can cause acute or chronic poisoning. In China, the mercury content in the air is not allowed to exceed 0.01~0.02 mg/ ^m3 , and the maximum allowable concentration of mercury and its compounds in industrial wastewater is 0.05 mg/l. [next]
In order to protect the environment from pollution and protect the health of workers, mercury should be restricted. Some countries in foreign countries have banned the use of amalgam. China is only a few gold mines and small mines in some places still use amalgam. For the selection of plants with amalgamation operations, mercury poisoning must be protected: (1) Develop a strict amalgam operation system. Mercury-containing vessels should be sealed to prevent mercury from evaporating and escaped; protective equipment should be worn during mercury amalgamation to avoid direct contact between mercury and skin; food, food, and smoking should not be stored in rooms with mercury. (2) The amalgamation workshop and the alchemy room should be ventilated, and the operation of mercury paste washing should be carried out in a closed operation cabinet with an air suction device. (3) having a factory floor where the job should be selected with mercury does not absorb mercury masonry material, made of ground slope of 1-3%, with the walls should be kept smooth surface, regular use soap and water or a solution of potassium permanganate (1 : 1000) Scrubbing. (4) Mercury collection devices should be installed in the sewage wells under the operating cabinet and outside, so as not to lose mercury. (5) The workshop with mercury operation is regularly cleaned by manganese dioxide absorption method, and the absorption rate of mercury vapor in air oxygen can reach 99%.
(C) floating flotation with gold wash method is one way of processing gold ore veins most widely used gold processing plant. In most cases, the flotation method is used to treat sulfide minerals containing gold ore with high floatability, the most significant effect. Because flotation can not only maximize the gold into the sulfide mineral concentrate, but also waste tailings, the cost of dressing is low. Flotation is also used to treat multi-metal gold ores, such as gold - copper, gold - lead, gold - antimony, gold - copper - lead - zinc - other minerals such as sulfur. For this type of ore, the flotation process can effectively select various gold-bearing sulfide concentrates, which is conducive to the comprehensive recovery of mineral resources. In addition, so-called "refractory ores" that cannot be directly treated by amalgamation or cyanidation are also required to be treated by a combined process including floatation. Of course, the flotation method also has limitations; for coarse-grained inlays, ores with a gold particle size greater than 0.2 mm, and for quartz-bearing gold-bearing ores without sulfides, it is difficult to obtain a stable flotation foam after slurrying, using flotation The law has difficulties.
In recent years, the flotation process of gold ore has made great progress, mainly in the innovation of process, the development of new agents, and the improvement of design. The use of stage grinding and stage selection process is the current development trend of flotation gold selection. Most foreign gold selection plants use two or even three sections. China's Suichang Gold Mine and Xiangxi Gold Mine use two-stage grinding and two-stage selection. Process and gold recovery rate increased by 2~6%; changing the pharmaceutical system, using a variety of agents to add, can also improve the gold selection effect of the Yanchang Gold Mine and the Jinchang Gold Mine with butylamine black and yellow medicine mixed, The recovery rate of gold is increased by 2 to 5%.
Since the flotation method can only maximize the concentration of gold into various sulfide mineral concentrates, and can not finally obtain the finished gold, there are only a few gold selection plants that use a single flotation process, generally using flotation as a joint process. A process is adopted. At present, China's gold selection plants using a single flotation process include gold mines such as Tunchang and Xiuyan, as well as small gold mines in some local groups.
(4) The cyanidation method has been used for nearly 100 years since the application of gold and silver in mines in 1887, and the process is relatively mature. Because of its high recovery rate and strong adaptability to ore, it can be used as a real estate gold, so it is still one of the main methods of gold production.
The cyanidation process can be divided into agitating cyanidation and diafiltration cyanidation. Stirring cyanide for the treatment of re-selected, mercury-contained tailings and flotation of gold-bearing concentrates, or for total mud cyanidation; and diafiltration cyanidation for the treatment of flotation tailings and low-grade gold-bearing ores Heap dipping and so on.
Conventional cyanidation process is a very mature process, including the preparation of leaching raw materials; stirring cyanide leaching; countercurrent selection of solid-liquid separation; leachate purification and deoxidation; zinc powder replacement and pickling; smelting ingots and other main operations. . The principle process flow is shown in Figure 1.

Figure 1 Process flow chart of conventional cyanidation principle [next]

1. Preparation of leaching raw materials: usually, the produced ore is crushed, ground (or ore-elected) to prepare a slurry suitable for cyanide leaching. Grinding fineness depends on the embedding characteristics of natural gold. For gold-bearing quartz vein ore, it is generally ground to 60~70%-200 mesh; while for sulfide mineral gold-bearing ore, it is mostly flotation and enrichment, and the concentrate is reground to 90~95%-325 mesh; for arsenic or The ore with high pyrrhotite is subjected to flotation concentrate roasting, desulfurization and arsenic removal, and calcination is carried out for cyanidation; in addition, there is an ore containing high carbon and interfering with cyanide leaching, which needs to be leached after chlorination and oxidation.
2. Stirring cyanide leaching: under the conditions of slurry concentration of 35~50%, pH value of 10~10.5 and cyanide concentration of 0.03~0.06%, fully agitate and leaching for more than 24 hours. More than 95% of the gold is dissolved as a gold cyanide complex. Its reaction formula is

4Au+8NaCN+O ₂ +2H ₂ O→4NaAu(CN) ₂ +4NaOH

The stirring leaching tank has two types: mechanical stirring type and air stirring type. In the past, China's gold cyanide plant used a stirred tank for flotation and slurry mixing as a leaching tank. It has few varieties and high power consumption and has been gradually eliminated. With the rapid development of gold production, on the basis of digesting and absorbing foreign advanced equipment, several large-scale new energy-saving leaching tanks have been developed, such as ф3000 × 8500 mm air stirring leaching tank, ф3000 × 5000 axial flow mechanical stirring leaching Slots, etc., especially the double impeller hollow shaft air inlet type stirring leaching tank, large volume, low power consumption, hollow shaft intake, so that air can be better dispersed into the slurry through the impeller, which can improve the leaching effect and reduce The pressure and air volume of the air supply system, which in turn reduces the installation power of the air compressor. Therefore, it is a relatively advanced leaching tank recognized at home and abroad. The specifications and technical performance of the double-wheel and hollow-shaft air intake mechanical stirring and leaching tank series designed by Beijing Nonferrous Metals Design and Research Institute are listed in Table 2.

Where V is the total volume of the desired leaching tank, m ³ ;
Q-day processing of ore, t/d;
T—the required leaching time, hr;
δ _t — ore density, g/cm ³ or t/m ³ ;
R-leaching slurry solid ratio;
K-leaching tank volume utilization coefficient: flotation gold concentrate cyanide K = 0.8 ~ 0.88; mud cyanide K = 0.9 ~ 0.95.
The leaching tank is selected based on the calculated total volume, and then the number of leaching tanks is calculated. It should be noted that the general cyanidation leaching is 4 to 8 stages, so the number of leaching tanks should not be less than 4. [next]
The leaching tank is fixed according to the volume of the tank volume. The air agitation tank is 0.013 to 0.025 m ³ /m ³ •min; the mechanical agitation tank is 0.002 m ³ /m ³ •min.
3. Countercurrent selection of solid-liquid separation: In order to fully separate the cyanide leaching solution and the leaching residue, multiple single-layer or multi-layer concentrators are generally used to form multi-stage countercurrent washing; multi-stage filtration washing is adopted by a filter; The concentrator and the filter constitute a combined washing. The latter is more common abroad, while the domestic ones mainly use a single-layer or multi-layer concentrator for multi-stage countercurrent washing.
The three-layer concentrator is widely used because of its continuous operation, reliable operation, convenient management, low power consumption and reduced floor space. The calculation of the three-layer concentrator is the same as that of the single-layer concentrator used in general concentrators. For the structural reasons, the three-layer concentrator has only one type of central transmission. The technical specifications of the three-layer concentrator currently used in production are listed in Table 3.

Calculation of multi-stage countercurrent washing process: It is assumed that the amount of ore discharged from the washing operations at all levels is equal to that of the ore; the solids contained in the overflow of the washing and washing at all levels are neglected; there is no leaching in the washing operation, and liquid gold does not occur. precipitation. According to the liquid balance of the countercurrent washing process and the principle of liquid gold balance, the formula for the countercurrent washing efficiency of each stage can be derived:

[next]

Wherein E ₁ , E ₂ , E ₃ , E ₄ , E5 - washing efficiency of each level, %;
F—the ratio of washing water to ore (washing ratio);
R—the liquid-solid ratio of the concentrating machine at all levels;
L—the liquid-solid ratio of the slurry after leaching;

a _wash - wash water containing gold grade;; a ₁ - the first grade thickener liquid contains gold grade.
Example: The known cyanide ore contains 52g/ton of gold, the leaching rate is 96.15%, the leaching concentration is 33.33%, the concentration of the concentrator of the washing and concentrating machine is 50%, and it is diluted to 20% and then enters the lower concentrator. The new water does not contain gold.
According to the known conditions, L = 2, R = 1, K = 0, F = 3, the washing efficiency, the grade of the liquid, and the results of the liquid discharge grade calculated by the above method are shown in Table 4.

4. Purification and deoxidation of leachate: The leachate (your liquid) obtained from the washing operation usually contains a solid suspension of 70 to 80 ppm or more. In order to prepare conditions for the zinc powder replacement operation, it is necessary to reduce the suspended matter content in the noble liquid to 5 to 7 ppm. The oxygen content is reduced to less than 1 ppm, so the noble liquid is purified and deoxidized.
At present, the precious liquid purification equipment used in production has a plate and frame type vacuum filter and a tube filter, and the deoxidation is realized by a vacuum deoxidation tower.
Plate-and-frame vacuum filter: It is a rectangular groove with several filter plate frames inside. One end of the plate frame is connected with the vacuum manifold outside the slot, and the plate frame is coated with a filter bag. During production, diatomaceous earth of 1~2 mm thick should be coated on the filter cloth as a filter aid. When the precious liquid is fed into the tank, the liquid is sucked to the deoxidation operation through the filter cloth, and the solid suspended matter remains in the filter cloth. Surface, for purification purposes. When the resistance on the filter increases and the flow rate is reduced to maintain normal production, flush the filter cloth with high-pressure water or wash off the scale on the filter cloth with dilute hydrochloric acid (5%).
According to the production practice data of some cyanide plants, the production quota of plate-and-frame vacuum filter is 2.7 m ³ /m ³ • The daily plate-type vacuum filter has a simple structure, convenient production and good purification effect, but the filter cake is inconvenient to clean. Every week, the water is washed one by one, and the labor intensity of the workers is large. Less used in newly designed cyanide plants.
Tubular filter: It is the most widely used and good precious liquid purification equipment in production. It consists mainly of a lower cone-shaped filter tank and 36 filter tubes (see Figure 2). The porous filter tube is coated with a filter cloth bag. When filtering, the solution is fed into the liquid pipe by the lower side of the tank body, and enters the filter tube through the filter cloth, and the filter residue is left on the filter cloth, and the clean liquid is discharged from the upper part of the filter tube through the collecting pipe. Thereby achieving the purpose of solution purification. When the slag is discharged, the compressed air is blown back from the liquid discharge port of the collecting pipe to the inside of the filter pipe, so that the filter cake is removed from the filter cloth and discharged from the slag discharge port at the bottom of the cone.
The tubular filter currently used in production is only one meter in size.

Figure 2 Tubular filter
1 - tank; 2 - filter; 3 - collecting tube; 4 - connecting branch; 5 - bracket [next]

Deoxidation tower: it is a bottom cone cylindrical tower body, the upper part of the tower is equipped with a solution shower, the middle part is a plastic point packing layer, the packing pile is supported by the sieve plate at the lower part of the tower, and the deoxidizing liquid storage chamber is below the sieve plate, and There is a level control device (see Figure 3). The solution in the deoxidation tower is taken from the top of the vacuum suction tower, and is sprayed onto the packing layer by the shower. Under the action of vacuum, the dissolved gas in the liquid is taken out to achieve the purpose of deoxidation. The deoxidizing liquid is sucked out by the pump at the discharge port of the cone bottom and pressed into the replacement operation.

Figure 3 Deoxygenation tower
1—watering device; 2—outer casing; 3—dot wave packing; 4—inlet pipe; 5—liquid level adjustment system;
6—Butterfly valve; 7—vacuum tube; 8—vacuum gauge; 9—level indicator; 10—inlet

The deoxidizing tower vacuum in production is generally 9.06 ~ 9.6 × 10 ⁴ Pa, the deoxidation rate can reach more than 95%, and the oxygen content of the deoxidizing liquid is below 0.5 g/ ^m3 . Currently deaeration tower plant cyanide used are Ñ„1000 × 3000; Ñ„1200 × 3600; Ñ„1500 × 3600; Ñ„1800 × 4000 millimeters, etc. several specifications. The supporting vacuum equipment of the deoxidizing tower generally uses a water jet pump.
5. Zinc powder replacement and pickling: The gold cyanide complex in the solution is replaced with zinc powder to precipitate gold. In order to obtain a more efficient displacement reaction of the zinc powder, a lead salt of about 0.005% and a cyanide concentration of about 0.05% should be maintained in the solution.
The main equipment for zinc powder replacement is the plate and frame filter press. During production, the filter frame of the filter press and the pressing surface of the filter plate should be cleaned, buttered, and double-layered filter cloth. After compaction, first hang a layer of 2 to 3 mm on the filter cloth. The diatomaceous earth is used as a filter aid, and then a certain amount of zinc powder is hung, and finally the pressure is added to the noble liquid to which the zinc powder is added, and the replacement reaction is completed when the precious liquid passes through the zinc powder layer on the filter cloth. The filter press removes the filter cake (ie, gold mud) every half month or month. The gold mud contains 30-40% water.
The gold mud contains a large amount of residual zinc and other splashing metals, which are removed by pickling to obtain high-grade gold mud.
6. ingot smelting: gold clay and flux generally 1: 0.8 to 1 ratio, i.e., 30 to 40% borax, saltpeter 25%, 15 to 20% quartz sand, 5 to 10% fluorite, soda other, Manganese oxide, etc. The slag is smelted at a furnace temperature of 1000 to 1100 ° C for about 3 hours to obtain a gold ingot (composite gold) containing 85% or more of gold and silver.
China's gold cyanide plant was founded in the 1960s. Over the past 20 years, it has made great progress in the improvement of process flow and the development of new equipment. The Jinchangyu and Zhaoyuan gold mines use two dip and two washing processes to improve the recovery rate of gold. The ф6～15m three-layer washing and concentrating machine is used for multi-stage countercurrent washing to save investment and floor space. For the replacement of zinc powder, the use of tube filter to purify the noble liquid, improve the quality of the product; replace the past bleaching method with the chlorination method and the acidification method on the cyanide-containing sewage treatment, which greatly saves the sewage treatment cost and the quality of the mixture. Further electrolysis realizes gold and silver separation and the like.
At present, cyanide in China is mainly treated with quartz vein containing gold ore, quartz-pyrite ore, quartz-chalcopyrite-pyrite ore, which is closely related to sulfide symbiosis. After sulphide mineral concentrate, it is treated by cyanidation. Such gold deposits as Jinchangyu, Linglong, Xincheng, Jiaojia and Wulong belong to this type.
The whole mud cyanidation is mainly used to treat low-sulfide gold-bearing oxidized ore quartz vein ore and absorb high mud ore, such as Chiweigou, Tuanjiegou, Haigou, Chaihulanzi, Damaoqi gold mine.

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