Selective liquid-liquid extraction of palladium(II) from hydrochloric acidmedia by di-(2-ethylhexyl) thiophosphoric acid (DEHTPA)

Liquid-liquid extraction of Pd(II) from hydrochloric acid solutions using d i-(2-ethylhexyl) thiophosphoric acid (DEHTPA or HL) dissolved in kerosene h as been studied. The distribution equilibrium of DEHTPA between the aqueous phase and the organic phase was investigated by treating the data with the computer program LETAGROP-DISTR. The extraction of Pd(II) from HCl solutio ns by DEHTPA was studied as a function of several variables: equilibration time, organic phase diluent, HCl and DEHTPA concentrations as well as tempe rature. Experimental equilibrium data were analyzed numerically using the p rogram LETAGROP-DISTR and the results showed that Pd(II) extraction can be explained assuming the formation of PdL2 complexes in the organic phase. DE HTPA was found to be selective for Pd(II) against Pt(IV), Rh(III), Cu(II), Fe(III) and Zn(II). The back-extraction of Pd(II) loaded in the organic pha se using different stripping reagents is also reported.