Extraction of iron(III) with bis(2-ethylhexyl)phosphinic acid and bis(2-ethylhexyl)phosphoric acid: experimental equilibrium study

The distribution equilibrium of iron(III) between bis(2-ethylhexyl)phosphin ic acid dissolved in hexane and acidic aqueous nitrate media has been inves tigated as a function of the concentration of extractant in the organic pha se and the concentration of hydrogen ion and iron(III) the in aqueous phase . The extraction characteristics of bis(2-ethylhexyl)phosphoric acid toward iron(III) are also evaluated and compared with those of bis(2-ethylhexyl)p hosphinic acid. The stoichiometry of the extracted species is determined on the basis of slope analysis. Iron is extracted by a cation-exchange mechan ism as FeR3. 3HR by both extractants. The temperature dependence of the ext raction equilibrium is examined by the temperature variation method to esti mate the apparent thermodynamic functions (Delta H, Delta S, and Delta G). Both extraction processes are exothermic in nature, and an increase in temp erature is not favorable.