Flotation slurry adsorption and gold and silver recovery

1. Characteristics of gold adsorption from the cyanated pulp of flotation concentrate
The resin adsorbs gold from the cyanated pulp of flotation concentrate. Because there are flotation agents, mercury and other impurities in the pulp and higher grade gold than the original ore, it has some different characteristics.
The presence of flotation reagents in flotation concentrates has a very adverse effect on the use of resins to adsorb gold from the cyanide slurry of flotation concentrates. Therefore, the flotation concentrate is usually washed with water in the thickener to remove the flotation agent before the cyanidation or resin adsorption. During the adsorption leaching process, AM-2 oxime resin has a strong adsorption effect on butyl xanthate ions, so the ions will occupy part of the reactive groups of the resin, reduce the capacity of the resin to adsorb gold, and regenerate the resin in the next step. At the time, the elemental sulfur is precipitated by the decomposition of xanthate under the action of caustic soda and sulfuric acid, and a precipitate of insoluble sulfide is formed on the surface of the resin, so that the resin is gradually "poisoned".
The foaming agent in the pulp also complicates the adsorption leaching process of the flotation concentrate. When the cyanide concentrate is stirred by compressed air in the Pachuca tank, the compressed air will form a large amount of foam in the foaming agent, and the thickness of the slurry is 1.5~2m, so that it is difficult for the naked eye or the meter to determine the true slurry level. . Therefore, in many cases, the effective volume of the Pachuca slot is only 70% to 80%.
Washing the flotation concentrate with fresh water can greatly reduce the foaming, but it cannot be completely eliminated. A method of suppressing foam by using an additive has been studied, and it is most effective to add lime milk.
Mercury in the slurry reacts with cyanide to form a soluble mercury cyanide complex and is adsorbed by the resin. At this time, the adsorption amount of mercury is generally the same as that of gold, so that the adsorption rate of gold is lowered. During the regeneration process, mercury is easily desorbed from the resin by the thiourea solution and easily enters the cathode deposit during the electrolytic recovery of gold. The harmful effect of mercury is that its vapor contaminates the plant together with hydrogen cyanide. For this reason, the flotation reagent consumption should be minimized during the ore flotation stage.
The slurry is heated to carry out the adsorption process under elevated temperature conditions, which can enhance the adsorption of gold on the resin and the dissolution of gold. Usually, the residual heat of the thermal eluent of the resin regeneration section can be utilized, and the slurry is preheated by the heat exchanger before entering the adsorption tank.
Since the content of gold in the flotation concentrate is much higher than that in the original ore, the amount of resin to be added in the concentrate cyanide slurry must be 1.5 to 2.0 times that of the original ore.
2. Adsorption and recovery of silver from cyanide pulp with high silver content For gold-bearing ore with high silver content, a factory in the US uses AM-2B anion exchange resin to process silver from cyanidation using a two-stage cyanidation-adsorption process. Gold and silver are recovered from high gold ore. [next]
In the solution of the co-existence of complex anions of gold, silver and other metals, the adsorption selectivity of AM-2B anion exchange resins is arranged in the following order: [Au(CN) 2 ] - >[Zn(CN) 4 ] 2- >[Ni(CN) 4 ] 2- >[Ag(CN) 3 ] 2- >[Cu(CN) 4 ] 3- >[Fe(CN) 6 ] 4- . The above sequence indicates that the AM-2Б anion exchange resin has the highest affinity for the Au complex anion [Au(CN) 2 ] - and the affinity for the zinc complex anion [Zn(CN) 4 ] 2 , followed by the iron complex anion [Fe ( CN) 6 ] 4- has the least affinity. When the resin is saturated, it is substituted from the resin in the reverse order, i.e., the silver anion replaces the complex anion of copper and iron, and the metal anion can replace all other complex anions located to the right of it. This is the principle of the two-stage adsorption process for the AM-2Б anion exchange resin to selectively recover gold and silver by its adsorption. In the first stage of the process, the gold is adsorbed and recovered, and the recovered pulp is subjected to the second stage of adsorption and recovery of silver, and the two stages of saturated resin are separately regenerated and treated.
The two-stage cyanidation-adsorption process for recovering gold and silver in ore is to cyanide the ore slurry in the presence of NaCN with a mass fraction of 0.1% to 0.15% and CaO of 0.2% to 0.3% for 12 hours. Almost all dissolved, silver dissolved 50%. The slurry is sent to the first stage for adsorption. The resin is added from the last adsorption tank. After 2~3 adsorption, the resin will be saturated with silver, but as the resin (reverse with the slurry) moves to the subsequent adsorption, the silver on the resin will be replaced by a large amount of gold cyanide anion. The amount of gold adsorbed gradually increases. When moving to the first adsorption tank, the saturated resin discharged contains about half of gold and silver (sometimes more silver). In the first adsorption tank, about 98% to 99% of the dissolved gold is adsorbed and recovered by the resin.
After the first stage of adsorption, the concentration of cyanide in the slurry is increased to keep it at about 0.15%, and cyanidation is carried out again to further leaching and recovering the silver in the sulfide ore. The secondary cyanide slurry is sent to the second stage of adsorption, mainly adsorbing and recovering silver from the slurry, and recovering a small amount of redissolved gold. Therefore, the saturated resin contains more silver and less gold.

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