AbstractThe solvent-extraction properties of the sulfur analogs, both neutral and acid, of those organophosphorus compounds that have been used so extensively in solvent extraction have been investigated. These sulfur analogs have one or more oxygen atoms replaced by sulfur atoms. The neutral esters, trialkyl phosphorothioates, selectively extract Ag+and Hg+2from a nitric acid medium. In general, the acid esters, dialkyl phosphorothioic and -dithioic acids, extract from mineral acid solutions those metal ions that form insoluble sulfides. Dialkyl phosphorothioic acids appear to be more selective extractants than are the corresponding dithioic acids. The effects of various organic solvents, of concentration of mineral acid, and of concentration of dialkyl phosphorothioic and -dithioic acids were studied. The relative order of extraction and the limits of extraction were determined. The nature of the zinc di-n-butyl phosphorothioate and -dithioate complexes as they exist in the aqueous and organic phases were investigated.