Zinc powder cementation method 1894 begins recovering gold from gold-containing solution, which is currently the most widely used method. The equipment for zinc powder replacement used filter presses and displacement tanks early. Merrill Claufa, which was later developed, is a typical method in the zinc powder displacement precipitation method. Its equipment and methods have not only withstood the many years of production practice at the Merrill Crouch plant, but have also been selected by some of the world's major cyanide plants.
The zinc powder used in the zinc powder displacement precipitation method is obtained by distilling zinc. Zinc powder should contain 95% to 97% zinc, about 1% lead , and particle size less than 0.01mm (US regulations 97% -0.04mm). Both coarse zinc and ZnO reduce the displacement precipitation effect. The blue powder produced by the zinc smelting plant contains about 10% to 15% of ZnO, which is unfavorable for sinking gold. Because these ZnOs do not act as precipitates, they completely enter the gold mud. Zinc powder is easily oxidized and should be stored and transported in a sealed container.
First, the filter press zinc powder replacement precipitation method. This method consists of a tape or other type of feeder that continuously feeds the zinc powder into the conical mixing tank and replaces it in the filter (Fig. 1). The deaerator solution of the degassing tank is placed in a conical mixing tank and mixed with zinc powder to form a zinc slurry discharged from the bottom of the tank, and the rest is pumped with a submersible centrifugal pump (centrifugal pump immersed in a pool containing gold solution to prevent inhalation of air). The degassing liquid is combined with a filter press or a frame filter, and the filter is filtered to produce gold mud and separate the lean liquid.
Figure 1 Filter press zinc powder replacement equipment system
1-Degassing tower; 2-vacuum pump; 3-cone mixing tank; 4-feeder; 5-centrifugal pump
6-submersible centrifugal pump; 7-filter press; 8-gold mud tank; 9-lean tank; 10-centrifugal pump
Second, the displacement tank zinc powder replacement precipitation method. This is a method of gold displacement and precipitation in a displacement precipitator, the equipment used is shown in Figure 2. The displacement precipitator is a circular groove with a conical bottom. A frame of four spreading bag filters is mounted on the four walls corresponding to the slots, and is radially fixed to the center tube. The frame has a "U" shape with a filter at one end and a branch at the other end of the degreased liquid manifold. The gold stripping liquid manifold surrounds the outside of the tank body, communicates with the filter frame through the branch pipe, and the main pipe is connected to the vacuum pump and the centrifugal pump.
Figure 2 Displacement tank zinc powder replacement equipment system
1-degassing tower; 2-straight air pump; 3-submersible centrifugal pump; 4-mixing tank;
5-feeder; 6-displacement sedimentation tank; 7-bag filter;
8-center tube; 9-spiral pulp; 10-center shaft; 11-small impeller;
12-transmission mechanism; 13-branch; 14-main pipe and vacuum pump; 15-centrifugal pump
After the degassing solution and the zinc powder are mixed into the mixing tank, they are fed into the displacement precipitator from the bottom of the tank, and the zinc slurry rises along the central tube under the action of the propeller and the small impeller. The suction gold mud is deposited on the filter cloth by means of the vacuum pump, and the lean liquid permeation filter cloth is discharged from the manifold through the branch pipe. According to the production practice, the replacement of gold precipitates mainly does not occur when mixing with zinc powder, but when the gold-containing solution passes through the zinc powder layer on the surface of the filter cloth. In order to rapidly form a zinc powder precipitation layer on the surface of the filter cloth after the displacement of the displacement sedimentation tank, it is necessary to directly add zinc powder which forms more than half of the total amount of the zinc powder precipitation layer to the open displacement sedimentation tank at the start of filtration. Conducive to the precipitation of gold mud. Although the displacement sedimentation tank is open and the air is in direct contact with the surface of the zinc paste, the zinc paste is not as fast as the filtration speed is fast, and the stirring force of the slow-rotating propeller and the small impeller (for stirring the upper zinc paste) is weak. How much oxygen is inhaled. Since the gold sludge is intermittently discharged, when the continuous displacement precipitation is performed, 2 to 3 replacement precipitation tanks should be provided for alternate use.
Lead nitrate or lead acetate is dropped into the zinc powder surface from the mixing tank by a drip tube to form a lead film on the surface of the zinc powder to enhance the replacement capacity of the zinc powder. The lead salt is added in an amount of 10% by weight of the zinc powder. When the NaCN and CaO of the gold-containing solution are as low as 0.014% and 0.018%, respectively, the precipitation effect of gold is also very good. The gold-depleted liquid is measured once every hour by colorimetry, and if the gold content exceeds 0.15gâˆ•m 3, it returns to deal with. The consumption of zinc powder depends on the gold content of the gold-containing solution from 1 to 5 g âˆ•m 3 to 50 g/m 3 .
Third, the Merrill Craw factory continuously added zinc powder replacement precipitation method. The replacement operation of Merrill Claufa (Fig. 3) is to directly pump the degassed mother liquor to the emulsifier, and the zinc powder is continuously added to the emulsifier through a zinc powder feeder and emulsified with the solution. The amount of zinc powder added is 15 to 70 g per ton of liquid. The precipitation of gold occurs essentially immediately after the addition of zinc. The emulsified solution was replaced in a vacuum precipitation chamber and gold was precipitated. After a suitable time, more than 99% of the gold in the solution is reduced and precipitated, and the poor liquid contains about 0.02 g of gold. Filtration of the precipitate from the solution typically uses a Sock or frame filter or filter press, and more widely used is a Stellar filter. During continuous production, the period of cleaning the precipitate from the filter is 3 to 28 days. The cleaned sediment is sent to the smelted gold ingot.
Figure 3. Equipment system of the Merrill Crowe method (Woodcock, 1976)
Using computer-controlled continuous Merrill Crowe gold and silver plus zinc replacement MC2000 system, has been developed to complete the hydrometallurgical industrial companies, and applied to large American and Mongolia that states Grubbs Tucker gold. The system automatically samples every 15 minutes, automatically adjusts the amount of zinc powder added according to the measurement results, and automatically controls various operations.
Fourth, the use of filter press zinc powder cake filter replacement gold-containing cyanide solution, can reduce the consumption of zinc, improve the gold content of gold mud. The poor liquid contained in the zinc powder cake displacement can be reduced to trace amounts.
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