Sorption behaviour of Am on precorroded HLW glass in water and brines

Abstract

In the alteration layer of HLW glasses corroded in aqueous solutions, less soluble elements like REE, actinides and other elements are retained by sorption or by formation of secondary alteration products controlling the solution concentrations. In order to quantify the sorption effect on the retention of metal ions, first sorption tests with U, Th and Eu have been performed using precorroded, simulated HLW glass as substrate.To demonstrate that the sorption behaviour of Eu is also representative for homologue trivalent actinides additional sorption tests were performed with Am 241 in deionized water, NaCl and MgCl 2 brine. Distribution ratios R s (R s = Am sorb /Am sol × V/m) for Am were found independent of the starting concentration in the pH range 2 to 6. At higher pH, a high amount of Am-containing colloidal particles were detected. The R s values of Am show a strong increase with pH, quite similar to the R s values of Eu. In general, the sorption behaviour of Eu and Am is very similar in deionized water and in brines. Clay minerals formed in the gel layer as secondary phases during long-term glass corrosion are assumed to act primilary as strong sorbents. Therefore, the sorption of REE and Am onto synthetic poor crystalline smectite precursors and a "well crystallized" natural smectite is compared with the findings obtained from precorroded glass. The sorption of Am on the precorroded glass is found to be much stronger than the retention on the investigated pure clay phases, indicating a different number of active sites or occurance of a different sorption mechanism.

Structural incorporation of Cm(III) in trioctahedral smectite hectorite: A time-resolved laser fluorescence spectroscopy (TRLFS) study

“…Eventually, after contact with groundwater, clay minerals will form as secondary phases upon alteration of the waste matrix, e.g. HLW borosilicate glass, in the course of the geochemical evolution of the repository system over long periods of time (Abdelouas et al, 1997;Luckscheiter and Nesovic, 2002). Dissolution of various compounds of the multi-barrier system and subsequent reprecipitation of secondary clay minerals may occur.…”

27 Radiochemistry

“…It has been shown that uranium ions can be incorporated into haematite 229 and that radioactive iodine is adsorbed from solution by colloidal ferric hydroxide. 230 Other studies have investigated the adsorption of thorium on cement 231 and on ammonium molydophosphate, 232 of americium on glass 233 and of strontium-85 and -89 by rotting tree bark and similar biomass materials. 234…”

TRLFS characterization of Eu(III)-doped synthetic organo-hectorite

“…Eventually, if the waste matrix gets into contact with ground water, clay minerals may form as secondary phases upon alteration of the waste matrix in the course of the geological evolution of the repository system (Abdelouas et al, 1997;Luckscheiter et al, 2002). For example, the trioctahedral sme ctite hectorite has been identified in long ^term corrosion experiments as one of the secondary phases forming in the alteration layer of HLW glass under near ^field conditions (Zwicky et al, 1989).…”