Retention Properties of Humic Substances onto Amorphous Silica: Consequences for the Sorption of Cations

Abstract

Silica / Humic substances / Actinides / Retention / Surface complexation model / Radwaste disposals SummaryThe Sorption of humic substances (Aldrich humic acids, fulvic acids from a granitic site) onto a amorphous silica has been investigated as well as their role on the sorption properties of tri-and hexavalent actinides (Am(III) and U(IV) respectively) onto this sorbent. Retention experiments have been performed (by batch procedures) in 0.1 M NaC104 electrolyte solutions in a pH ränge of 3-10 with humic and fulvic concentrations representative of those encountered in natural waters (1 -10 ppm). According to the oxidation State of the cation and the humic/ fulvic concentration, the actinide sorption behavior is enhanced or decreased compared to the system without humic substances and is related to the complexation strength of this cation towards the organic ligand. The complexation surface model (with no electrostatic term) has been applied in order to describe the mechanisms occurring at the oxide-water interface; apparent surface complexation constants have been determined for each species (cation, organic ligand) and surface reactions with the hydroxyl surface groups of silica surface are proposed.

On the study of Th(IV)-humic acid interactions by competition sorption studies with silica and determination of global interaction constants

“…This is the case for silica at pH > 6.5, as shown on Fig. 2, as already shown in the case of silica surface [54,55,75], or on clay [76]. Furthermore, contrary to oxalic acids, humic acids do not appear to increase feldspar dissolution rate [77].…”

“…The presence of a competing ligand such as HA can strongly influence the retention of heavy metals onto mineral phases [51][52][53][54][55][56]. Although mechanisms involved in the sorption of HS onto mineral surfaces [57,58] are not fully understood, many general trends are well known.…”

“…Zachara et al [53] have shown that when HA and the mineral are pre-equilibrated, cobalt (II) retention is more pronounced when the amount of HA is less than needed to saturate the mineral surface. When the concentration of HA surpasses the saturation of the mineral surface, LabonneWall et al [54], Takahashi et al [55] and Reiller et al [56] reported that metal cation retention decreases with increasing pH. These effects depend upon the relative proportions of HA and mineral phase sorption sites.…”

Comparison of complexed species of Eu in alumina-bound and free polyacrylic acid: A spectroscopic study

“…The interaction depends on the chemical state of the organic material, which can be soluble or associated to mineral particles. Numerous studies on the interaction of actinides with HS in solution are described in the literature [1][2][3][4], but few studies have been devoted to the interaction of actinides with HS-mineral complexes [5][6][7][8][9][10][11][12][13].…”

Distribution coefficient Kd of transuranics in soils : Experimental determination and consequences for dose assessment

“…Many researches have improved the knowledge of the mechanisms relevant to the mobility of transuranians in the geosphere, aiming at better wastes disposals impact assessments [1][2][3][4][5]. In surface soils americium, usually trivalent and thus expected to have a simple behaviour by comparison with multivalency elements, is still far from being completely elucidated [6,7]; its mobility, connected with the formation of mobile species, either with soluble organic species [8][9][10][11][12][13] or with small clay particles, producing pseudo-colloids [14,15], is particularly weak.…”