Solvent extraction separation of vanadium(V) from multivalent metal chloride solutions using 2‐ethylhexyl phosphonic acid mono‐2‐ethylhexyl ester

The solvent extraction behaviour of vanadium(V) from hydrochloric acid solutions has been investigated using 2‐ethylhexyl phosphonic acid mono‐2‐ethylhexyl ester (EHEHPA ≡ HX) in kerosene as an extractant. For comparison, extraction studies have also been carried out with vanadium(IV). The results demonstrate that the extraction of vanadium(V) follows the cation exchange mechanism:$$ {{\hbox{VO}_{2}}^{+}}_{\rm aq} + (\hbox{HX})_{2_{\rm org}} {\buildrel K_{\rm ex,V(V)} \over \Leftrightarrow} \hbox{VO}_{2}\hbox{X}\cdot \hbox{HX}_{\rm org} + {\hbox{H}^{+}}_{\rm aq} $$ where (HX) 2 refers to the dimeric form of EHEHPA. On the other hand, two dimeric molecules of EHEHPA were found to be involved in the extracted complex of vanadium(IV):$$ {\hbox{VO}^{2+}}_{\rm aq} + \hbox{2(HX)}_{2_{\rm org}} {\buildrel K_{\rm ex,V(IV)} \over \Leftrightarrow} \hbox{VOX}_{2}\cdot \hbox{2HX}_{\rm org} + {\hbox{2H}^{+}}_{\rm aq} $$ The equilibrium constants of the above extracted complexes have been calculated and found to be K ex,V(V)  = 3.14 and K ex,V(IV)  = 0.32. The effect of the nature of the diluent on the extraction of vanadium(V) with EHEHPA has been studied and correlated with the dielectric constants. IR spectral studies of the extracted complex were used to further clarify the nature of the extracted complex. The separation and recovery possibilities of vanadium(V) from other associated metal ions, viz magnesium(II), aluminium(III), titanium(IV), chromium(III), manganese(II) and iron(III), which are present in the waste chloride liquors from the processing of titanium minerals, are also discussed. © 2002 Society of Chemical Industry