You are hereList Methods of Elution; Zinc cyanide Elution + Others
List Methods of Elution; Zinc cyanide Elution + Others
Elution: Consist i n pass a volume of eluant solution through a resin bed with the objective of obtain a solution with high concentration of gold. Similarly to activated carbon, elution is sometimes a difficult operation. One of the first procedures of elution employed a mixture of acetone, hydrochloric acid, and water, and was possible obtain a recovery of 99.9% of the gold present in a bed of Amberlite IRA-400 resin. However, there was a problem, acetone is a flammable reagent and the risk of inflammability was very high.
Base metals loaded in weak base resins can be eluted quantitatively and its concentration trends to increase when eluate is recycled to the process. This could allow the recovery the some metal with economic importance.
Some methods of elution are listed below:
A. Zinc cyanide Elution. This method employs a zinc cyanide solution which is passed through a resin bed. The rich solution obtained can be sent to a Merryl-Crowe process or electrowinning, and the zinc cyanide solution can be recycled to elution. In this method all the anionic cyanide complexes are eluted efficiently and the resin can be regenerated to full capacity each cycle with efficient recycle of chemicals. [7]
A number of factors contributed to the choice of this eluant. Firstly, zinc cyanide is cheap and is compatible with existing gold processes. Secondly, it is a very effective eluant because strong base resins have a higher capacity for zinc cyanide than for gold or silver cyanide. It is especially effective it continuous electrolytic extraction of gold and silver is incorporated in the elution cycle. Finally, absorption and elution are carried out in alkaline cyanide solution of high pH. This result in reduced losses of resin due to osmotic shock, and also could prevents the formation of cobalticyanide species. These species form in acid solution and poison anion exchange resins.
Ther e are disadvantages such as resins have to be chemically regenerated after elution, slow kinetics, and toxicity of hydrocyanic gas produced during regeneration. During elution, the resin is loaded with zinc cyanide. The reaction is as follows:
2] - +NR3Au(CN)2- + Zn(CN)4-2 = ( ] - +NR3)2Zn(CN)4-2 + Au(CN)2-
Before being reutilized, resin must be regenerated with diluted acid at pH less than 3. The reaction is as follows:
(] - +NR3)2 Zn(CN)4-2+ 4HCl = 2] - +NR3Cl + ZnCl2 + 4HCN
This method was developed at Mintek and the loaded strong base resin was eluted with a zinc cyanide solution containing 25 to 30 g/l and a slight excess of cyanide (ratio zinc to cyanide is 1 to 5). The solution obtained was sent to an electrochemical cell where the gold was removed. In this elution procedure, an elution of more than 90% of all the other metal ions in the resin was achieved.
