Institute of Chemistry and Chemical Technology SB RAS, Federal Research Сenter “Krasnoyarsk Science Сenter” Siberian branch of Russian Academy of Sciences, Krasnoyarsk, Russia:

N. A. Grigorieva, Senior Researcher, e-mail: natasha@icct.ru
I. Yu. Fleitlikh, Leading Researcher
N. I. Pavlenko, Leading Researcher

The data on the extraction of silver from nitric (nitrate) and hydrochloric acid solutions by a new highly efficient extractant: bis (2,4,4-trimethylpentyl) dithiophosphinic acid disulfide in toluene are given in this work. The stability of L in solutions of HNO₃ was studied using IR spectroscopy. It is shown that the extractant is stable up to 3.0 mol/dm³ of HNO₃. At concentrations ≥3.0 mol/dm³, a change in the spectra was observed associated with the appearance of sulfoxides and sulfones, which indicates a partial degradation of the extractant. An increase of nitric acid concentration leads to a decrease in the silver extraction due to the formation of a newly extracted complex [L·(AgNO₃·HNO₃)_n] (where n = 1–4) in the organic phase which, along with the partial decomposition of the extractant, leads to a deterioration of silver extraction. An increase of hydrochloric acid concentration leads to a decrease in the silver extraction due to the formation of non-extracting anionic silver complexes in the aqueous phase (AgCl₂, AgCl₃ и AgCl₄). The stability of L for five cycles of extraction — stripping in the extraction of silver from hydrochloric acid solutions using thiourea solution (0.75 mol/dm³) mixed with sulfuric acid (0.5 mol/dm³ H₂SO₄) as the re-extractant was made. The high stability of the extractant was shown — the distribution coefficients of silver did not change from cycle to cycle. Recommendations are given on the composition of aqueous solutions for effective silver extraction by disulfide while maintaining a high stability of the extractant.

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