Silver extraction from nitrate solutions with the disulfide of bis(2,4,4-trimethylpentyl)dithiophosphinic acid

In this paper, we present the data on silver extraction from nitrate solutions with the disulfide of bis(2,4,4-trimethylpentyl)dithiophosphinic acid (L) in toluene. Based on the analysis of the extraction data and the IR and electronic absorption spectra of the extracts, it was concluded that silver extraction is due to the formation of the compound [(AgNO3)nL] in the organic phase, with n = 1–4. In the extracted complexes, the silver ion is chelated to the sulfur atoms, while the nitrate ion is in the outer sphere. A study of the effect of the solvent on the extraction of AgNO3 with the disulfide showed that solvent extraction efficiency decreases in the series chloroform > toluene > decane > octyl alcohol, which is due to the preferential solvation of the extracted complex by the solvent. A decrease in the extraction of silver when using octyl alcohol resulted from the predominant interaction of the alcohol with the extractant, rather than with the extracted compound. It was shown that the disulfide can be used to recover silver from nitric acid solutions containing metal impurities (Ni, Cu, Co, Zn, Fe(III), and Na). The degree of silver recovery in one stage was 99.82%, while the separation factors of silver over the impurity metals (βAg/Me) ranged from 30,000 to 400,000 indicating a high selectivity of the extractant towards silver. Almost complete silver stripping from the loaded organic phase is achieved with a mixture of thiourea or ammonium rhodanide and sulfuric acid solutions. •AgNO3 extraction with the disulfide of CYANEX 301 was studied.•The composition of the extracted complex was found to be [(AgNO3)nL], where n = 1–4.•The degree of silver recovery in one stage was 99.82%.•The separation factors of silver over metals (βAg/Me) ranged from 30,000 to 400,000.