title: Extended X-ray absorption fine structure investigation of adsorption and separation phenomena of metal ions in organic resin.
abstract: Analytical technique using organic resins has already been well-developed, and its applications are employed in various fields; nevertheless, the chemical phenomena occurring inside the resin remain unclear for the most part. In the present study, we apply EXAFS spectroscopy to elucidate the adsorption and separation phenomena of metal ions by organic resin. That is, the chemical species of trivalent lanthanides (Ln(III)) adsorbed in a tertiary pyridine resin from hydrochloric acid and nitric acid solutions have been determined by EXAFS. The results in HCl solutions suggest that Ln(III) ions are partly dehydrated in the resin phase, enabling the pyridine groups of the resin and chloride ions to coordinate to the Ln(III) ions in their primary coordination sphere. On the other hand, Ln(III) ions are tightly coordinated by several nitrate ions in HNO3 solutions and they keep forming the nitrate complex even in the resin phase. The lighter Ln of Nd tends to form an anionic nitrate complex, [Nd(NO3)4.nH2O]-, in the resin phase, while the middle Ln of Sm exists as a cationic nitrate complex, [Sm(NO3)2.nH2O]+, for the most part. On the basis of these EXAFS results, the adsorption and separation mechanisms of the pyridine resin in HCl solutions are interpreted as the direct coordination of pyridine groups to metal ions, while the mechanisms in HNO3 solutions are mainly dominated by the anion-exchange reaction between the protonated pyridine groups and the anionic nitrate complexes of Ln(III). The obtained results demonstrate that the hydration of metal ions weakens, and instead, other complexations are enhanced in the resin phase.
authors.affiliation: Synchrotron Radiation Research Center (SPring-8), Japan Atomic Energy Agency, Kouto 1-1-1, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan. aikeda@lax.kuramae.ne.jp
authors.forename: Atsushi
authors.initials: A
authors.lastname: Ikeda
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Yaita
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Okamoto
authors.forename: Hideaki
authors.initials: H
authors.lastname: Shiwaku
authors.forename: Shinichi
authors.initials: S
authors.lastname: Suzuki
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Suzuki
authors.forename: Yasuhiko
authors.initials: Y
authors.lastname: Fujii
mesh_terms: D000327:Adsorption; D006851:Hydrochloric Acid / Q000737:chemistry; D007475:Ion Exchange Resins / Q000737:chemistry*; D007477:Ions / Q000032:analysis; D028581:Lanthanoid Series Elements / Q000032:analysis*; D015394:Molecular Structure; D017942:Nitric Acid / Q000737:chemistry; D011725:Pyridines / Q000737:chemistry*; D012680:Sensitivity and Specificity; D012996:Solutions / Q000737:chemistry; D013057:Spectrum Analysis / Q000379:methods; D013499:Surface Properties; D014965:X-Rays
chemical_list: D007475:Ion Exchange Resins; D007477:Ions; D028581:Lanthanoid Series Elements; D011725:Pyridines; D012996:Solutions; D017942:Nitric Acid; C023666:pyridine; D006851:Hydrochloric Acid