Solvent extraction of silver from chloride media with some commercial sulfur-containing extractants

Different kinds of commercial sulfur-containing extractants (SFI-6R, MSP-8, Cyanex 302 and Cyanex 301 in EXXSOL D-80) were examined to extract silver from chloride media. The aggregation of MSP-8 was analysed quantitatively by means of vapor-pressure osmometry and it was found that this extractant exists as a dimeric species in aliphatic organic diluents. Extractants containing P = S and P(S)SH functional groups strongly extract silver in the whole concentration range of hydrochloric acid except for the very high concentration region, while SFI-6R only weakly extracts silver in the low concentration region and no extraction was observed in the high concentration region. Extraction equilibrium of silver with SFI-6R was measured by the slope analysis method, while for MSP-8, Cyanex 302 and Cyanex 301 the complex stoichiometries were inferred using Job's method. It was elucidated that silver is extracted as 1:2 metal:reagent complex with extractants containing one donor atom of sulfur, while the ratio becomes to 1:1 for an extractant having two sulfur donor atoms.