Silver Extraction from Hydrochloric Acid Solutions with the Disulfide of Bis(2,4,4-trimethylpentyl)Dithiophosphinic Acid

Silver extraction from hydrochloric acid solutions with the disulfide of bis(2,4,4-trimethylpentyl)dithiophosphinic acid (L) in toluene is described in this work. Based on the analysis of the extraction data, it was concluded that silver extraction is due to the formation of the compound AgCl.2L in the organic phase. An increase in the concentration of hydrochloric acid in the aqueous phase leads to a decrease in AgCl extraction because of the formation of non-extractable anionic complexes of silver. Solvent extraction efficiency decreases in the series octanol > decane > chloroform > toluene, which is due to the preferential solvation of the extracted complex by the solvent. A significant increase in the extraction of silver chloride with disulfide in the presence of octanol is caused by the strong interaction of the extracted compound and the alcohol, due to the chloride ion solvation by octanol. The possibility of using the disulfide for silver extraction from hydrochloric acid solutions containing metal impurities (Ni, Cu, Co, Zn, Fe (III), and Na) has been demonstrated. The degree of silver recovery in one stage was 98.62%, while the extractant showed high selectivity toward silver: the separation factors of silver over metal ((Ag)/(Me)) ranged from 9000 to 30,000. Almost complete silver stripping from the organic phase was achieved when using a mixture of thiourea and sulfuric acid solutions. The extraction characteristics of the disulfide are much better as compared to that of the well-known commercially available extractant triisobutylphosphine sulfide. The disulfide of bis(2,4,4-trimethylpentyl)dithiophosphinic acid can be used for efficient extraction of silver from industrial hydrochloric acid solutions of different origin.