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

International audienceTo model the influence of humic substances on the migration of tetravalent actinides (Pu, Np, U) in and around nuclear waste repositories we have immobilized humic acid on silica gel and investigated its complexation of Th(IV). It is anticipated that this material might serve as a geochemical model of the humate-coated minerals that are likely to be present in the vicinity of the repositories. The binding of Th(IV) by the immobilized humic acid was examined at pH 4, 5 and 6 in 0.1mol/L$^{-1}$ NaClO$_4$ by the batch method. Th(IV)-humate conditional interaction constants have been evaluated from data obtained from these experiments by using non-linear regression of binding isotherms