Adsorption study of U and Th by N, O-hybrid donor ligand-immobilized hydrogels. Issue 12 (13th August 2019)

• Record Type: Journal Article
• Authors: Nakase, M.; Yamamura, T.; Shirasaki, K.; Nagai, M.; Takeshita, K.
• Is Part Of: Separation science and technology. Volume 54:Issue 12(2019)
• Page Start: 1952
• Page End: 1959
• Publication Date: 2019-08-13
• Subjects: Gel/liquid extraction -- uranium -- thorium -- adsorption -- thermosensitive gels; Separation (Technology) -- Periodicals; 660.284205
• DOI: 10.1080/01496395.2019.1575881
• Languages: English
• ISSNs: 0149-6395

Abstract

ABSTRACT: The thorium (Th) fuel cycle is attracting attention again because of its potential merits over the uranium (U) fuel cycle, but the associated back-end technology remains insufficiently mature compared with that of the U fuel cycle. In the chemical reprocessing of spent Th oxide fuels, effective separation of UO2 2+ from Th 4+ is required and a quite high dose rate is expected in reprocessing because of the strong radiation by 208 Tl generated from 232 U, an associated product of 233 U. Therefore, gel/liquid extraction was applied to U/Th separation．Introducing ligands chemically into the hydrogels (via the C–C bonds) can minimize ligand leaching, and the ligands are expected to be more resistant to radiation. Some of the N, O -hybrid donor ligands that have polymerizable functional groups – Bis(di- N -allyl- N -tollyl) phenanthlorine diamide (Allyl-Tol-PTDA) and N, N, N', N' -tetraallylpyridine-2, 6-dicarboxamine (Tet-Allyl-PDA) for gel adsorbent synthesis and N, N, N', N' -tetrahexylpyridine-2, 6-dicarboxamine (Tet-Hex-PDA) – were synthesized for solvent extraction because Allyl-Tol-PTDA has low solubility in n -dodecane. Allyl-Tol-PDA and Tet-Allyl-PDA were then polymerized with N -isopropylacrylamide (NIPA) and N, N' -methylenbisacrylamide (BIS) to give thermosensitive hydrogels, namely PTDA-gel and PDA-gel. The general extraction behaviors of Allyl-Tol-PTDA and Tet-Hex-PDA instead of Allyl-Tol-PDA and the adsorption behaviors of PTDA-gel and PDA-gel were compared with those of UO2 2+ and Th 4+ in HNO3 . Consequently, differing extraction/adsorption behavior between solvent extraction and gel adsorption was determined. The PTDA gel showed no strong dependency on acidity and temperature with UO2 2+, but Th 4+ showed a local maximum with varying acidity. By contrast, the PDA-gel showed temperature dependency: UO2 2+ adsorbed more at higher temperature and Th 4+ adsorbed more at lower temperature. Therefore, U/Th separation is possible with (i) PTDA-gel at higher temperature and acidity, and (ii) PDA-gel at higher temperature and lower acidity.