Tank and vat leaching involves placing ore, usually after size reduction and classification, into large tanks or vats at ambient operating conditions containing a leaching solution and allowing the valuable material to leach from the ore into solution.
Cyanide tank construction
Cyanide tanks are the main facilities for tank leaching process, which are often of rectangular shape. The size and quantity of the cyanide tank are based on the capacity, local conditions and leaching time. The bottom of the cyanide tank tilts to the discharging end; the obliquity is about 0.8%. The height of the tank is about 1.5m. There is a false floor about 100-200mm high above the tank bottom. The materials made of the false floor should be economical and easy to obtain from local conditions. The common false floor is made of wood bars or bamboo rafts with rush mats or bamboo mats on it.
Materials loading After the false floor in the cyanide tank is ready, dry the tailing under the sun and grind it to powders. The tailing powders are loaded into the tank by labor, belt conveyor or loader, and then, rake the tailing powders smooth. The tailing powders should be put into the tank evenly and porously. Lime is used as protective alkali and loaded into the tank with the materials.
Leaching The tailing powders are loaded into the cyanide tanks; in the first leaching process, solid sodium cyanide is put into a mixer to make 10% solution, which is diluted to 0.2% leaching agents; put the leaching agents to the tank till the liquid is 50-100mm high above the tailing powders; then, stop adding the agents; let the tailing powders immerse in the liquid for 3-4 hours; when the time is up, discharge the liquid to its most, and after about one or more hours, the tailing powders will become porous; then, 0.08% leaching agents are put into the tank for second leaching process; after a certain time, 0.06% leaching agents are used for the third time leaching, and so on and on; about 7 days later, stop leaching and discharge all the liquid.
Discharging After the leaching process, get the tailing out of the tank by labor, belt conveyor or loader, and then, put into new tailing powders again.
Adsorption The pregnant liquor discharged from the cyanide tank is pumped to the adsorption tower, where the activated carbon adsorbs the gold and the barren liquor flows to the barren liquor tank.
Desorption, electrolysis and smelting Gold-loaded carbon goes through the desorption and electrolysis process or burning process to get the gold mud, which is smelted to get the gold bar.