Complexation of Technetium with Humic Acid

Abstract

The complexation of technetium with well characterized humic acid, which was extracted from one of the Gorleben groundwaters in northem Germany, was studied. It was found that technetium humate was produced as a brownish-black precipitate by addition of Sn^^ as a reductant in a mixture Solution of pertechnetate and humic acid at pH 4 in 0.1 mol P' NaC104. This precipitate could be distinguished from the TCO2 with respect to the dissolution behavior at higher pH. The produced amount of the formed technetium humate linearly increases with the added amount of Sn^ * with a slope of ca. 0.5, showing that the valence State of technetium is 3 + . With decrease of the concentration of humic acid in the Solution, the formation of TCO2 became prominent.The stock Solution was warmed after addition of H2O2 to guarantee complete oxidation to pertechnetate. The radioactivity measurements were carried out using a liquid scintillation counter (Aloka LC700). Proton exchange capacity, 5.38 meq g"' [5], of the humic acid (Gohy 573 HA) was used to indicate the HA concentration.

Evidence for the existence of Tc(IV) – humic substance species by X-ray absorption near-edge spectroscopy

“…The exact nature of the interacting Tc(IV) species is unknown and can range from monomeric to polynuclear forms. These measurements are the first direct Brought to you by | New York University Bobst Library Technical Services Authenticated Download Date | 5/28/15 3:40 PM indications of the interaction between Tc(IV) species and humic substances in neutral to alkaline reducing environments, and are complementary to the observations of Tc(III) interaction with humic substances by Sekine et al [4] in acid pH.…”

“…Under oxidising conditions, technetium is present as pertechnetate (TcO 4 − ), a highly soluble, anionic species, that does not sorb significantly on minerals or sediments [1]. Under suitable reducing conditions, and especially in the presence of a reducing solid phase, which acts as an electrondonor, TcO 4 − is reduced to probably Tc(IV). Because Tc(IV) is easily hydrolysed, a surface precipitate is formed [2].…”

“…Stalmans et al [3] observed an association between technetium-99 and humic substances and proposed an interaction between TcO 2+ species and humic substances. On the other hand Sekine et al [4] concluded from an indirect measurement that in presence of humic acids, Tc(III) species are formed and associate with the humic acids. However these experiments were done at low pH (pH = 4).…”

Quantification of the Interaction of Tc with Dissolved Boom Clay Humic Substances

“…On the other hand, Sekine et al (5) concluded by an indirect measurement that, in the presence of humic acids, Tc(III) species were formed and associated with the humic acids. But these latter experiments were made at pH < 4 and in the absence of HCO3 -.…”

Comportement de radionucléides (Cs, I, Sr, Se, Tc) dans le sol : proposition de valeurs de Kd par défaut

“…La sorption du technétium est corrélée principalement aux teneurs en carbone organique, en oxydes de fer et d'aluminium et en argile des sols (Gu et Schulz, 1991). Les formes réduites du technétium forment des complexes très stables avec la matière organique, en particulier avec les acides humiques (Sekine et al, 1997 ;Henrot, 1989 ;Stalmans et al, 1996). Le technétium est ainsi majoritairement présent dans les horizons organiques du sol.…”