Technology for recovering gold from thiourea solution

A metal complex of thiourea stability and cationic character such that there are several ways of selecting gold recovery.
Rodschchkov and Pan Chinke studied the adsorption of gold from acidic thiourea solution with activated carbon. According to their observation, the amount of gold contained reached 15%-17% of the mass of activated carbon.
The gold-thiourea complex was subjected to solvent extraction using several extractants. Qi Li Yake ear (1977) by determining the tributyl phosphate (TBP) from thiourea - optimum conditions for recovering gold in hydrochloric acid solution. Tributyl phosphate has been used in flotation processes for the recovery of gold from thiourea hydrochloride solutions (Balnova, 1972). She observed an increase in gold recovery from 67% (pH = 1) to 99% (pH = 8); an increase in extraction time, an increase in extraction rate and partition coefficient. One of the reforms in the process was the enrichment of gold using polyurethane foam (Braun and Farah Road, 1973) loaded with tributyl phosphate.
Some strongly acidic cation exchange resins extract gold from acidic thiourea solutions, while weakly acidic resins are not suitable for recovery of gold in the presence of thiourea. The exchange fiber synthesized with polyvinyl alcohol (Zhujun et al., 1975) can effectively adsorb gold from thiourea and thiourea hydrochloride solution, and the ability to exchange gold is 15-23 mg/g (fiber), for silver . Poor adsorption. Chelly Jacques et al. studied a novel inorganic ion exchanger for recovering gold from a thiourea solution. They test compound such as zirconium phosphate in exchange agent such as iron and lead cyanide, e.g., aluminum ferrocyanide exchange capacity of gold 85mg / g (exchanger), eluting the adsorbed gold with a concentrated solution of an acidic thiourea However, after the gold is desorbed, the adsorption capacity is lowered.
A large amount of research has been conducted on the elution of gold from a gold cyano complex saturated resin with a thiourea solution (Tatalu et al.). This operation can recover precious metals, and after absorbing HCN with NaOH solution, the alkaline cyanide solution can be recycled. The precious metal is then recovered by sintering or electrolysis. The method has been changed to include electroplating of gold and silver from an ion exchanger, whereby the thiourea solution is simultaneously used for elution and electrolytic deposition of precious metals. A method for reducing gold-thiourea to metal by electrolytic deposition is proposed by Masley et al. Electrolysis can be carried out in the presence of thiourea; however, sulfur generated by thiourea decomposition (thiourea anodization) will be detrimental to the cathode. Tatalu (1968) found that properly stirring the electrolyte and controlling the current density below 250 A/m2 would eliminate this trouble to some extent. The use of a membrane tank separated from the cathode chamber can eliminate the contamination of the cathode by sulfur and avoid spontaneous dissolution of the cathode due to the oxidant generated in the anode reaction. However, the ability to produce pure gold products with thiourea solutions has not been confirmed in production.

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