The zinc wire replacement process for the recovery of gold from cyanide solution began in 1889. The zinc wire displacement sedimentation tank (Fig. 1) is generally wood, steel or concrete. It is usually divided into 5 to 10 grids, with a total length of 3.5 to 7 m, a width of 0.45 to 1 m, and a depth of 0.75 to 0.9 m. The screen is placed on the iron frame with a hole diameter of 3.36 to 1.68 mm (the mesh is 6 to 12 mesh). The zinc wire is turned into a scrap of 0.02-0.04 mm thick and 1 to 3 mm wide by metal zinc on a lathe, or the molten metal zinc is continuously and uniformly poured on a water-cooled high-speed rotating pig iron cylinder to form pellets.
Figure 1 Zinc wire replacement sedimentation tank
1-box; 2-box edge; 3-lower baffle; 4-upper baffle;
5-screen frame; 7-zinc wire; 8-gold mud; 9-vent; 10-handle
When the gold-containing solution flows through the tank, the contact time with the zinc wire is about 17 to 20 minutes, and during this time, about 99% of the gold is replaced. In the production practice, the handles fixed at the center of the screen are gently lifted up and down regularly to loosen the zinc wire and release hydrogen bubbles, and the gold mud is separated from the zinc wire to sink the bottom of the groove. After a period of time, the old zinc wire that can continue to be used in the box is moved to the first few cells of the box, and the new zinc wire is added to the next few cells, so that the solution containing low gold and the new zinc wire with strong replacement force can be obtained. Contact, increase the precipitation rate of gold. When loading the zinc wire, it must be loosened and spread evenly. Pay special attention to the four corners in each grid to prevent the solution from flowing through the cavity and reduce the replacement effect.
The sedimentation tank usually releases gold mud once or twice a month. After the extracted zinc wire is separated into gold mud by a cylindrical sieve, the sieved zinc wire is used for the next batch replacement. The gold mud is discharged from the discharge port and filtered and recovered in a filter box or a filter press.
Although the zinc wire replacement method has the advantages of simple equipment, easy operation, and no power consumption, the zinc wire consumption is large (4 to 20 kg of zinc is required for the production of 1 kg of gold), and the consumption of NaCN is also large (due to the expensive use of the zinc wire replacement method). The liquid is generally not degassed, zinc will oxidize in a high oxygen solution to form a white precipitate), the gold mud contains high zinc and the equipment occupies a large area. Therefore, the zinc wire replacement method has been replaced by the zinc powder replacement method in large and medium-sized mines.
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