I&EC 32 |
| Akhilesh Tripathi, Dmitri Medvedev, Jose Delgado, and Abraham Clearfield. Department of Chemistry, Texas A & M University, P. O. Box 30012, college station, TX 77843-3255 |
| Two approaches were pursued to modify the structure of the synthetic titanosilicate analog (HK 3Ti4O4(SiO4)3•4H2O, K-TSP) of the mineral pharmacosiderite (KFe4(AsO4)3 (OH) 4•7H2O) in order to change its ion exchange properties. These structural modifications were based on our conclusions regarding the origins of selectivity that were derived from structural work on the closely related titanosilicate (TS) with sitanakite topology. In the first approach four samples with increasing Ge substitution for Si were prepared in order to increase the unit cell volume of TSP and thus to modify the position of Cs cations. Since the ionic radii of Ge4+ (0.40 A) is larger than Si4+ (0.26 A) in tetrahedral coordination, its substitution in tetrahedral Si site increases unit cell volume while its substitution in octahedral Ti4+ (0.605 A) site decreases unit cell volume. While the substitution at octahedral site was kept as low as possible via variation of synthesis, the substitution at tetrahedral site was increased to a level that the fourth sample has complete substitution of Si by Ge. In the second approach novel 20% Nb substituted K-NbTSP was synthesized and its selectivity was compared with K-TSP and germanium germanate pharmacosiderite (K-GeGeP). The substitution of Nb5+ for Ti4+ in the framework decreases the amount of charge balancing cations required in the channels and hence can modify ion exchange behavior. In this report the modified ion-exchange behavior in light of these changes will be discussed from structure perspective. We gratefully acknowledge the U.S. Department of Energy, Energy Research and Development Administration Grant No. 01-00398 with funds supplied through Westinghouse Savannah River Technology Center. [1]. A. Tripathi, D. Medvedev, M. Nyman, A. Clearfield, J. Solid State Chem., 2003, 175, 72-83 [2]. E.A. Behrens, D. M Poojary, and A. Clearfield, Chem. Mater. 1998, 10, 959-967 [3]. E.A. Behrens, D. M Poojary, and A. Clearfield, Chem. Mater. 1996, 8, 1236-1244 |
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Advanced Technologies for Decontaminating and Managing Radioactive Wastes
1:30 PM-4:20 PM, Sunday, March 28, 2004 Marriott -- Orange County 2, Oral
Division of Industrial and Engineering Chemistry |
