U(VI) sorption on Ca-bentonite at (hyper)alkaline conditions – Spectroscopic investigations of retention mechanisms

Philipp, T.; Azzam, Salim Shams Aldin; Roßberg, André; Huittinen, Nina; Schmeide, Katja; Stumpf, Thorsten

doi:10.1016/j.scitotenv.2019.04.274

Cited by 33 publications

(21 citation statements)

References 67 publications

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“…This can be explained by the difference in pCO 2 of around 0.25 log units between both scenarios (Figure 6d,h). With increasing concentration of dissolved carbonate in the system, sorption of uranium decreases due to the formation of ternary complexes [50][51][52][53] as already discussed by Hennig et al [16]. This in turn means, the lower the pCO 2 value of the considered system, the higher are the associated sorption capacities for uranium and the influence of the geochemical gradient on the migration lengths is consequently diminished as can be seen in our simulation results (Figure 7a).…”

Section: Geochemical System Governs Uranium Migrationsupporting

confidence: 79%

Potential Uranium Migration within the Geochemical Gradient of the Opalinus Clay System at the Mont Terri

Hennig

Kühn

2021

Minerals

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Transport properties of potential host rocks for nuclear waste disposal are typically determined in laboratory or in-situ experiments under geochemically controlled and constant conditions. Such a homogeneous assumption is no longer applicable on the host rock scale as can be seen from the pore water profiles of the potential host rock Opalinus Clay at Mont Terri (Switzerland). The embedding aquifers are the hydro-geological boundaries, that established gradients in the 210 m thick low permeable section through diffusive exchange over millions of years. Present-day pore water profiles were confirmed by a data-driven as well as by a conceptual scenario. Based on the modelled profiles, the influence of the geochemical gradient on uranium migration was quantified by comparing the distances after one million years with results of common homogeneous models. Considering the heterogeneous system, uranium migrated up to 24 m farther through the formation depending on the source term position within the gradient and on the partial pressure of carbon dioxide pCO2 of the system. Migration lengths were almost equal for single- and multicomponent diffusion. Differences can predominantly be attributed to changes in the sorption capacity, whereby pCO2 governs how strong uranium migration is affected by the geochemical gradient. Thus, the governing parameters for uranium migration in the Opalinus Clay can be ordered in descending priority: pCO2, geochemical gradients, mineralogical heterogeneity.

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Section: Geochemical System Governs Uranium Migrationsupporting

confidence: 79%

Potential Uranium Migration within the Geochemical Gradient of the Opalinus Clay System at the Mont Terri

Hennig

Kühn

2021

Minerals

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“…The alteration of concrete leads to release of NaOH, KOH, and Ca(OH) 2 which shifts the pH of the pore water towards the hyperalkaline region (pH > 12) 8 , which in turn can alter the retention potential of host rock minerals towards radionuclides as shown by Philipp et al . 9 .…”

Section: Introductionmentioning

confidence: 99%

Cm(III) retention by calcium silicate hydrate (C-S-H) gel and secondary alteration phases in carbonate solutions with high ionic strength: A site-selective TRLFS study

Wolter

Schmeide

Huittinen

et al. 2019

Sci Rep

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We studied the Cm(III) retention by calcium silicate hydrate (C-S-H), portlandite (Ca(OH)2) and their alteration products calcite, vaterite, and aragonite in high ionic strength carbonate-containing solutions representing specific formation waters. For this, we synthesized C-S-H gels with calcium to silicon (C/S) ratios of 1.0 and 2.0 in the absence and presence of Cm(III), resulting in Cm(III)-free and Cm(III) doped C-S-H gel, respectively. For phase identification purposes we applied X-ray diffraction (XRD) while for the identification of the Cm(III)/C-S-H binding mode we applied site-selective time-resolved laser-induced luminescence spectroscopy (TRLFS). The stability of Cm(III) doped phases under repository-relevant conditions was evaluated by studying the time-dependent release of Cm(III) from the Cm(III) doped C-S-H gel into leaching solutions containing 0.02 M NaHCO3 or 2.5 M NaCl/0.02 M NaHCO3 over 60 d. Speciation changes of Cm(III) due to leaching were followed with TRLFS while C-S-H structure alterations and secondary phase formation were monitored with XRD. From the results it could be concluded that Cm(III) is not mobilized by aqueous carbonate but either remains incorporated in the C-S-H structure and portlandite or becomes partially re-immobilized into secondary CaCO3 phases. The presence of NaCl led to an accelerated conversion of metastable secondary CaCO3 phases into calcite.

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“…3), showing that uranium clearly exists in the uranium(VI) stability field. The Ca 2 UO 2 (CO 3 ) 3(aq) species is characterized by a low sorption affinity to minerals as was shown, for instance, for ferrihydrite and quartz (Fox et al 2006), clay (Joseph et al 2013;Philipp et al 2019), and granite (Schmeide et al 2014). Brooks et al (2003) have shown that calcium uranyl carbonate complexes inhibit microbial reduction of uranium(VI) under certain conditions.…”

Section: Thermodynamic Calculationmentioning

confidence: 96%

Uranium and neptunium retention mechanisms in Gallionella ferruginea/ferrihydrite systems for remediation purposes

Krawczyk-Bärsch

Scheinost

Roßberg

et al. 2020

Environ Sci Pollut Res

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The ubiquitous β-Proteobacterium Gallionella ferruginea is known as stalk-forming, microaerophilic iron(II) oxidizer, which rapidly produces iron oxyhydroxide precipitates. Uranium and neptunium sorption on the resulting intermixes of G. ferruginea cells, stalks, extracellular exudates, and precipitated iron oxyhydroxides (BIOS) was compared to sorption to abiotically formed iron oxides and oxyhydroxides. The results show a high sorption capacity of BIOS towards radionuclides at circumneutral pH values with an apparent bulk distribution coefficient (Kd) of 1.23 × 104 L kg−1 for uranium and 3.07 × 105 L kg−1 for neptunium. The spectroscopic approach by X-ray absorption spectroscopy (XAS) and ATR FT-IR spectroscopy, which was applied on BIOS samples, showed the formation of inner-sphere complexes. The structural data obtained at the uranium LIII-edge and the neptunium LIII-edge indicate the formation of bidentate edge-sharing surface complexes, which are known as the main sorption species on abiotic ferrihydrite. Since the rate of iron precipitation in G. ferruginea-dominated systems is 60 times faster than in abiotic systems, more ferrihydrite will be available for immobilization processes of heavy metals and radionuclides in contaminated environments and even in the far-field of high-level nuclear waste repositories.

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U(VI) sorption on Ca-bentonite at (hyper)alkaline conditions – Spectroscopic investigations of retention mechanisms

Cited by 33 publications

References 67 publications

Potential Uranium Migration within the Geochemical Gradient of the Opalinus Clay System at the Mont Terri

Potential Uranium Migration within the Geochemical Gradient of the Opalinus Clay System at the Mont Terri

Cm(III) retention by calcium silicate hydrate (C-S-H) gel and secondary alteration phases in carbonate solutions with high ionic strength: A site-selective TRLFS study

Uranium and neptunium retention mechanisms in Gallionella ferruginea/ferrihydrite systems for remediation purposes

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