- Email: [email protected]
“Anion” exchangers
J, Inorg. Nucl. Chem., 1966, Vol. 28, p. 695. Pergamon Press Ltd. Printed in Northern Ireland
LETTER TO T H E E D I T O R
"Anion" exchangers (Received 14 September 1965) IN A RECENTpublication MARPLEtl~ has shown that the exchange equilibria of anionic complexes can be treated on the basis of the partition of an uncharged complex. For liquid anion exchangers, it has been pointed out t2~ that exchange equilibria can equally well be thought of either as the exchange of an anionic complex or the adsorption of a neutral species, and that the same alternative routes exist for resinous ion exchangers "although they are seldom emphasized". For liquid anion exchangers, kinetic, rather than equilibrium, experiments have given rigorous proof of the simultaneous existence of these alternative routes: 8~ This is not so remarkable if one considers that in most anion exchangers the simple anion is bonded by ion-pairing to the rest of the structure, so that to some extent it can act as a free anion. In the aqueous phase, it may or may not be possible to form an anionic complex of a cation, because of competition between ligand anions and water molecules, but the anion exchanger can act as a source of "pure" ligand anions. Extraction of a neutral complex can therefore take place by the replacement of a water molecule in the primary co-ordination sphere of the central atom by a ligand anion which is bonded to the structure of the exchanger, in a manner completely analogous to the formation of anionic complexes from a neutral complex in the aqueous phase. The conclusion is inescapable--the term "anion exchanger" when referring to the exchange of complex species is in many instances a misnomer.
Government Metallurgical Laboratory Johannesburg
P" J" LLOYD
tl~ L.W. MARPLE,J. Inorg. NucL Chem. 27, 1693 (1965). tal C. F. COLEMAN,Nucl. Sci. Eng. 17, 274 (1963). ta~ W. J. McDoWELL and C. F. COLEMAN,Paper No. 25K, 144th Amer. Chem. Soc. Meeting, Los Angeles, California (April 1963).
695
LETTER TO T H E E D I T O R
"Anion" exchangers (Received 14 September 1965) IN A RECENTpublication MARPLEtl~ has shown that the exchange equilibria of anionic complexes can be treated on the basis of the partition of an uncharged complex. For liquid anion exchangers, it has been pointed out t2~ that exchange equilibria can equally well be thought of either as the exchange of an anionic complex or the adsorption of a neutral species, and that the same alternative routes exist for resinous ion exchangers "although they are seldom emphasized". For liquid anion exchangers, kinetic, rather than equilibrium, experiments have given rigorous proof of the simultaneous existence of these alternative routes: 8~ This is not so remarkable if one considers that in most anion exchangers the simple anion is bonded by ion-pairing to the rest of the structure, so that to some extent it can act as a free anion. In the aqueous phase, it may or may not be possible to form an anionic complex of a cation, because of competition between ligand anions and water molecules, but the anion exchanger can act as a source of "pure" ligand anions. Extraction of a neutral complex can therefore take place by the replacement of a water molecule in the primary co-ordination sphere of the central atom by a ligand anion which is bonded to the structure of the exchanger, in a manner completely analogous to the formation of anionic complexes from a neutral complex in the aqueous phase. The conclusion is inescapable--the term "anion exchanger" when referring to the exchange of complex species is in many instances a misnomer.
Government Metallurgical Laboratory Johannesburg
P" J" LLOYD
tl~ L.W. MARPLE,J. Inorg. NucL Chem. 27, 1693 (1965). tal C. F. COLEMAN,Nucl. Sci. Eng. 17, 274 (1963). ta~ W. J. McDoWELL and C. F. COLEMAN,Paper No. 25K, 144th Amer. Chem. Soc. Meeting, Los Angeles, California (April 1963).
695