External amalgamation equipment and operation

Apparatus for amalgamation mainly has an outer plate and mixed with mercury amalgamation plate and tank mine operations to capture mercury (gold) or the like.

The mercury-mixing plate is a piece of tile that is lapped and mounted on a wooden (or steel) inclined groove surface, so it is also called a mercury-mixing tank. Moreover, since the mercury-mixing tank realizes the amalgamation operation by means of the mercury-mixing plate, it is customarily referred to as plate-mixing mercury. The mercury mixing tank has a fixed mercury mixing tank and a vibrating mixing tank.

Supply the mineral pool (or slurry distributor) with amalgam slurry. The box is a rectangular wooden box, and a small hole with a hole diameter of 30 to 50 mm is opened on one side of the mercury plate, so that the slurry flowing out of the wire is covered with the mercury plate. In order to make the slurry evenly cover the entire mercury plate, it is best to nail a movable diamond-shaped block in front of each hole for easy adjustment.

Mercury (gold) traps are used to capture mercury and mercury paste lost from the slurry from mercury plates. After the mercury trap is placed in the mercury plate, the slurry slows down the flow rate here so that the mercury and heavy minerals separate from the gangue by the difference in specific gravity. The ascending flow rate of the slurry in the mercury trap is usually 30 to 60 mm ∕s.

There are quite a few types of mercury traps. Figure 1 shows one of the simplest box-type mercury traps. The slurry flows from the mercury-mixing tank into the tank and flows back through the partition to flow from the overflow. Regularly remove mercury and mercury paste from the bottom of the tank. When the proportion of the material is large and the particles are coarse, in order to improve the mercury capture effect, a hydraulic mercury trap is often used. Figure 2 shows a type of hydraulic mercury trap. It adds water from the lower part of the mercury trap to cause pulsating water flow (150-200 times/min) to improve the stratification and separation of mercury and gangue.

Figure 1 Box type mercury trap

1-slot; 2-separator; 3-mercury and mercury paste; 4-slurry overflow

Figure 2 Hydraulic mercury trapping device

1. Mercury plate and its processing

Amalgamation plates are typically 3 ~ 5mm thickness purple silver plated copper plate, but also useful, the latter less effective copper plate. Like silver-plated copper plates, sterling silver plates are resistant to mineral acids and sulfides and have non-staining properties. They can form silver amalgam after mercury is applied, which can buffer the friction of the slurry and easily maintain a uniform mercury surface. Practice has proved that the recovery rate of using them as amalgam sheet metal is 2% to 5% higher than that of copper plate. However, the price of sterling silver plate is expensive, the investment cost is large, and the surface of the sterling silver plate is smooth, the amount of mercury is insufficient, and the effect of mercury amalgamation is often not as good as that of silver plated copper plate.

When using a copper plate to mix mercury, although the effect is poor, the silver plating process can be omitted, and the price is low. The copper plate is cut to the required size before use, and then annealed to make the surface loose and rough, and then grinded (mechanical or manual) with a raft or a grinding wheel to correct the non-flat surface or remove other defects. Finally, it is carefully washed with ammonium chloride or cyanide solution and rinsed with clean water. After a layer of mercury is sprayed on the working surface of the copper plate, mercury is mixed.

The processing method of the silver plated copper plate includes:

(1) Copper plate processing. Cut the copper plate into the required size, remove the surface oil stain by chemical method or heating method, and then use the raft to hit the flat surface. Finally, remove the burrs and marks on the copper plate with a wire brush and fine sandpaper and polish it before sending it to the plating.

(2) Preparation of electroplating solution. The plating solution used was an aqueous solution of potassium silver cyanide. The raw material for preparing 100L plating solution is 5kg of electrolytic silver, 9-11kg of pure nitric acid (90%), 8-9kg of salt, 12kg of potassium cyanide (98%-99%), and distilled water to 100L. The basic reaction of plating solution preparation is:

2Ag+4HNO ₃ 2AgNO ₃ +2H ₂ O+2NO ₂

AgNO ₃ +NaCl AgCl+NaNO ₃

AgCl+2KCN KAg(CN) ₂ +KCl

The plating solution is prepared by dissolving electrolytic silver in dilute nitric acid (nitric acid: water = 3:1) to prepare a silver nitrate solution, and then adding salt water to precipitate silver into silver chloride. Then, the precipitate was filtered, washed with water to neutrality, and dissolved in a potassium cyanide aqueous solution prepared in distilled water to prepare a plating solution containing 50 g of silver and 70 g of cyanide.

(3) Silver plating on copper plates. Copper plated silver is usually carried out in an electrolytic cell lined with soft plastic in wood or reinforced concrete, or in a plating bath made of ceramic or hard plastic. The slots are rectangular and the size depends on the size and number of silver plated copper plates required. The mercury plate used in a gold mine in China is 1.2m long, 0.5m wide and uses a wooden plating tank with a length of 1.6m, a width of 0.8m and a height of 0.6m.

Electroplating uses an electrolytic silver plate as an anode and is powered by a DC generator or a silicon rectifier. In China, it can also be powered by the 12V generator of Jiefang brand car. The operation was carried out under the conditions of a cell voltage of 6 to 10 V, an area current of 1 to 3 A/cm ² , and a liquid temperature of 16 to 20 °C. The thickness of the silver plating on the copper plate is 10 to 15 μm.

Second, the fixed type of mercury tank

The fixed amalgamation tank is a non-moving amalgamation tank with three types of flat surface (Fig. 3), stepped and intermediate belt collecting grooves (Fig. 4). In China, the use of flat mercury tanks, while the foreign use of trapping trenches. The tank with the intermediate belt collecting groove has the function of trapping the coarse-grained monomer gold, but there is also a disadvantage that the ore siltation is unfavorable to the operation. The stepped fixed amalgamation tank is formed in a stepped shape with a height difference of 30 to 50 mm per section. The slurry is well mixed to avoid delamination by the drop of the slurry flow, and the monomer gold can enter the bottom layer and the surface of the mercury plate. Get in good contact.

Figure 3 fixed mixing tank

1-bracket; 2-bed; 3-mercury plate (silver-plated copper plate); 4-slurry distributor; 5-side gang

Figure 4: Fixed mercury tank with trapping groove

1-mercury plate; 2-bed surface; 3-bracket; 4-slurry distributor; 5-trapping groove; 6-side gang

In order to facilitate silver plating and easy replacement and to facilitate gold-harvesting, the mercury-mixing plate is usually cut into blocks of 400-600 mm in width and 800-1200 mm in length, and is laid on the groove surface in a slanting direction in the inclined direction of the groove surface.

The size of the amalgamation plate is mainly determined by the amount of ore processed per day, the ore content of the ore and the role of the amalgamation process in the gold selection process. Under normal conditions, the thickness of the slurry fluid on the amalgamation plate is 5-6 mm, and the flow rate is 0.5-0.7 m∕s. At this time, the mercury plate of 0.05-0.5 m ² should be set for the daily treatment of 1 t ore. When different gold-bearing ores are mixed with mercury in different processes, the area of ​​mercury plate to be set per ton of ore per day is listed in Table 1.

Table 1 Production quota of amalgamation plate [m ² /(t·d)]

In production practice, the effect of the amalgamation plate depends mainly on the width of the mercury plate and not on the length of the mercury plate. The width of the mercury plate is appropriately larger, which makes the thickness of the slurry fluid on the surface of the plate thinner and evenly distributed, which is beneficial to the mercury amalgamation of gold. Since most of the gold is trapped at the front end of the mercury plate during amalgamation, it does not have much practical significance to increase the length of the mercury plate. Generally, when amalgam is used as an auxiliary device for internal amalgamation to capture mercury paste and mercury (gold), the mercury plate is about 5 to 6 m long. When the mercury amalgamation plate is used as an external amalgamation device, it is placed in the closed loop of the grinding machine and only the coarse gold is collected. The mercury plate length is 2 to 4 m.

The slope of the amalgam plate is determined by 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. Looking for a gold mine ball mill, the ore discharge size is 60% -0.074mm (200 mesh), the slurry concentration is 50%, and the mercury plate inclination angle is 10°. Another quartz vein type gold-copper grader has an overflow particle size of 55% to 60%, -0.074 mm (200 mesh), a slurry concentration of 30%, and a mercury plate inclination of 8°. Table 2 lists the slope of the mercury plate at different particle sizes and different pulp concentrations for ores having a density of 2.7 to 2.83 g∕cm ³ . When the other conditions are the same and the ore specific gravity increases, the inclination of the mercury plate should increase accordingly. If the ore density is 3.8 to 4.0 g/cm ³ , the slope of the mercury plate should be 1.2 to 1.25 times the value in the table.

Table 2 Mercury plate inclination