Investigation of complexation of thorium by humic acid using chemically immobilised humic acid on silica gel

Abstract : To model the influence of humic substances on the migration of tetra-valent actinides (Pu, Np, U) in and around nuclear waste repositories we have immobilized humic acid on silica gel and investigated Th(IV) complexation on it. It is anticipated that this material might serve as geochemical models of the humate-coated minerals that are likely to be present in the vicinity of the repositories. The binding of Th by the immobilized humic acid was examined at pH 4, 5 and 6 in 0.10 M NaClO4 by batch method. Th(IV)-humate conditional stability constants have been evaluated from data obtained from these experiments by using non-linear regression of binding isotherms. The results have been interpreted in terms of complexes of 11 stoichiometry.