Tl-208, Pb-212, Bi-212, Ra-226 and Ac-228 adsorption onto polyhydroxyethylmethacrylate-bentonite composite

Abstract

The adsorption of naturally occurring radionuclides (Tl-208(+), (212)pb(2+), Ra-226(2+), Bi-212(3+) and Ac-228(3+)) onto Polyhydroxyethylmethacrylate-bentonite (PHEMA-B) composite was investigated. Experimentally obtained isotherms were evaluated with reference to Langmuir, Freundlich and Dubinin-Radushkevich (DR) models. The adsorption isotherms were L type of Giles classification proving that PHEMA-B had a high affinity adsorbent for the studied radionuclides. The Langmuir adsorption capacities (XL) were in the order of (226)r. to (2.8 MBq kg(-1)) > Bi-212 (0.4 MBq kg(-1)) > (212)pb (0.3 MBq kg(-1)) > Ac-228 and (TI)-T-208 (0.2 MBq kg(-1)). The adsorption process was physical via complex formation after proton exchanger for which the adsorption energies obtained from DR model was evidence. The enthalpy and entropy changes were positive and the negative free enthalpy change was proof for the spontaneity of adsorption. The reusability tests for PHEMA-B for five uses demonstrated that the adsorbent could be reused after complete recovery of the loaded radionuclide ions by 1 M HCl. The chemical structure of the composite did not change after the reuses and storage foregoing. (C) 2011 Elsevier B.V. All rights reserved.