Effective methods for the recovery and/or separation of particular ions such as the transition, post-transition, lanthanide and radioactive actinide metal ions from solution mixtures of these and other metal ions, are of great importance in modern technology. It is particularly difficult to remove these particular metal ions in the presence of moderate to strong acids and soluble complexing or chelating agents, such as the halide ions, which have a high affinity for the desired metal ions. It is also difficult to remove the mentioned desired metal ions when they are present at low concentrations in solutions containing other metal ions at much greater concentrations. Hence, there is a real need for a process to selectively concentrate certain transition, post-transition, lanthanide and actinide metal ions when present at low concentrations and in the presence of acid solutions and other complexing agents.
It is known that siderophores (compounds manufactured by microorganisms to sequester Fe.sup.3+ ions) are commonly composed of hydroxamate- and catecholate-containing molecules. Formulas 1 and 2 show these structures. ##STR1##
A modern review of the siderophores is found in an article by J. R. Telford and K. N. Raymond, "Comprehensive Supramolecular Chemistry," vol. 10, Ed. by D. N. Reinhoudt, Pergamon Press, 1996, pp. 245-266. Many synthetic iron chelating agents have been prepared in an effort to find pharmaceutical compounds that will increase the excretion of iron from iron-overloaded patients. Some of the synthetic chelating agents contain the hydroxypyridinone structure as depicted by 3-hydroxy-2(1H)-pyridinone (Formula 3), 1-hydroxy-2(1H)-pyridinone (Formula 4), and 3-hydroxy-4(1H)-pyridinone (Formula 5). ##STR2##
These chelating agents often have other substituents, such as carboxyl groups in positions 3, 4, 5, or 6 of the compound in
Formula 4 or alkyl and carboxymethyl groups on the nitrogen atoms of the compounds in Formulas 3 and 5. These hydroxypyridinone structures are excellent complexing agents for Fe.sup.3+ because the pyridone carbonyl oxygen atoms withdraw electron density and have a partial negative charge as shown in the resonance structures for 1-hydroxy-2(1H)-pyridinone below. ##STR3##
Thus, these materials resemble the hydroxamate molecules that have a high affinity for Fe.sup.3+. The synthesis and Fe.sup.3+ ion-complexing properties of these types of compounds are found in the article by K. N. Raymond and his coworkers, "Ferric Ion Sequestering Agents. 13. Synthesis, Structures, And Thermodynamics of Complexation of Cobalt(III) And Iron(III) Tris Complexes of Several Chelating Hydroxypyridinones," Inorganic Chemistry, Volume 24, 1985, pp. 954-967; and in the article by P. D. Taylor and his Coworkers, "Novel 3-hydroxy-2(1H)-pyridinones. Synthesis, Iron(III)-chelating Properties And Biological Activity," Journal of Medicinal Chemistry, Volume 33, 1990, pp. 1749-1755. K. N. Raymond and his coworkers have found that having more than one of these chelating groups bonded to a polyamine such as 1,5,10,14-tetraazatetradecane improves their affinity for Fe.sup.3+ and allows complex formation with the actinides. Bonding to the polyamine is through the formation of amide bonds as shown in following Formula 6. ##STR4##
The octadentate ligand shown above in Formula 6 has a high affinity for Fe(III), Am(III), Pu(IV) and Np(V) as reported in articles by K. N. Raymond and coworkers, "Specific Sequestering Agents For The Actinides. 21. Synthesis And Initial Biological Testing of Octadentate Mixed Catecholate-hydroxypyridinoate Ligands," Journal of Medicinal Chemistry, Volume 36, 1993, pp. 504-509; and "In Vivo Chelation of Am(III), Pu(IV), Np(V) And U(VI) in Mice by Tren-(Me-3,2-HOPO)," Radiation Protection Dosimetry, Volume 53, pp. 305-309. A similar polyamine material containing three Formula 3 HOPO molecules formed strong interactions with gadolinium, calcium and zinc as shown in the article by J. Xu, S. J. Franklin, D. W. Whisenhunt, Jr., and K. N. Raymond, "Gadolinium Complex of Tris[(3-hydroxy-1-methyl-2-oxo-1,2-didehydropyridine-4-carboxamido)ethyl]a mine: A New Class of Gadolinium Magnetic Resonance Relaxation Agents," Journal of the American Chemical Society, Volume 117, 1995, pp. 7245-7246. The synthesis of hydroxypyridinonate chelating agents, such as that shown above in Formula 6, is shown by Raymond et al., U.S. Pat. No. 4,698,431, issued Oct. 6, 1987. The materials described in this patent and the above cited articles are directed only to the hydroxypyridinonate molecules or those bound to simple amines. Attachment of from one to four HOPO rings to a molecular or polymeric backbone through amide linkages is taught by Raymond et al., U.S. Pat. No. 5,624,901, issued Apr. 29, 1997. At least one of the HOPO rings must be a 3,2-HOPO ligand. Tetra-, hexa- and octadentate ligands (i.e. two to four HOPO substituents) are illustrated being attached to a polyamine linking backbone. There is also an allegation that a polymeric backbone, such as poly(styrenedivinylbenzene), agarose and polyacrylamide, having amine functionalities, can be used to which a HOPO substituent can be directly bonded via an amide-type linkage. There is no teaching or suggestion that a tetra-, hexa- or octadentate HOPO ligands, attached to a backbone carrier, can be covalently attached to a polymeric or inorganic solid support through the backbone carrier by appropriate linkage means.
The ability to complex Fe.sup.3+, Pu.sup.4+, Th.sup.4+, Zr.sup.4+, lanthanides, actinides and other metal ions under increasing acidities and competing matrix complexers or chelants requires the interactive strength of six to eight donor atoms, of which there are two per HOPO ring, and the proper molecular spacing of these HOPO rings. The ability to use this interactive strength to perform an actual separation requires that three or more HOPO moieties with appropriate molecular spacing be attached via a stable covalent bond to a hydrophilic membrane support in such a manner that the HOPO moieties cooperate in such a manner to maximize their collective binding abilities.