Stripping of Rh–Sn–Cl‐loaded alkylated 8‐hydroxyquiniline with Na 2 SO 3 –HCl

Acidic rhodium(III) chloride solutions pretreated with SnCl 2 at a ratio Sn(II) : Rh(III) = 3 are contacted with an alkylated 8‐hydroxyquinoline (Kelex 100) to prepare loaded organics which subsequently are subjected to stripping with Na 2 SO 3 –HCl solutions. Rh(III) was found to be stripped selectively involving the following reaction:$$[\hbox{RhCl}_{3} (\hbox{SnCl}_{3})_{3} (\hbox{H}_{2} \hbox{Q})_{3}]_{{\rm{(aq)}}} + {\hbox{2HSO}_{3}}^{-} \longrightarrow {\hbox{RhCl}_{2} (\hbox{SO}_{3})_{2}}^{3-} + \hbox{2H}^{+} + \hbox{Cl}^{-} + 3[\hbox{SnCl}_{3}{\cdot}\hbox{H}_{2} \hbox{Q}]_{{\rm{(org)}}}$$where H 2 Q is the protonated form of kelex 100. Direct characterization of the stripped complex and slope analysis confirmed this stripping reaction. Equilibrium was reached within 20 min. A kinetic analysis found the stripping process to be irreversible and to be controlled most probably by the slow release of SnCl 3 − ligand from the intermediate Rh–Q–SO 3 –SnCl 3 organic complex. Copyright © 2004 Society of Chemical Industry