Solubility of Ca(<scp>ii</scp>), Ni(<scp>ii</scp>), Nd(<scp>iii</scp>) and Pu(<scp>iv</scp>) in the presence of proxy ligands for the degradation of polyacrylonitrile in cementitious systems

Szabó, Péter; Tasi, A.; Gaona, Xavier; Polly, Robert; Maier, Annika Carolin; Hedström, Svante; Altmaier, M.; Geckeis, H.

doi:10.1039/d2dt01409b

Cited by 5 publications

(12 citation statements)

References 69 publications

(145 reference statements)

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“…1 This concentration is in line with previous data reported in the literature (Ochs et al, 2016) but higher than the solubility limit of β-Ni(OH) 2 (cr) determined under analogous boundary conditions (González-Siso et al, 2018;Szabo et al, 2022b). This observation suggests that this solid phase is neither present in the cement not forming within the timeframe of our experiments.…”

Section: Resultssupporting

confidence: 92%

“…The results obtained for the sorption of these radionuclides in the presence of proxy ligands are compared with analogous studies in the presence of ISA, which shares some structural similarities with HIBA and HBA. The present work complements and further expands the experimental studies by Szabo et al dedicated to the proxy ligands of UP2W, i.e., evaluating their effect on the solubility of selected radionuclides (Szabo et al, 2022b) and assessing their uptake by HCP (Szabo et al, 2022a). Frontiers in Nuclear Engineering frontiersin.org in a previous study (Altmaier et al, 2008).…”

Section: Introductionsupporting

confidence: 63%

“…After a contact time of 1 week, the initial leachate was separated by decantation from the HCP, and the solid material was equilibrated again with fresh Milli-Q water during one additional week. The same HCP material and cement pore water were used in the solubility and sorption studies with proxy ligands for UP2W degradation products (Szabo et al, 2022a;Szabo et al, 2022b). The composition of the cement porewater is buffered by portlandite at pH ≈ 12.5 and [Ca] ≈ 0.02 M, and is characterized by a low content of Na and K (≤3•10 −4 M).…”

Section: Cement and Cement Porewatermentioning

confidence: 99%

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Uptake of Ni(II), Eu(III) and Pu(III/IV) by Hardened Cement Paste in the Presence of Proxy Ligands for the Degradation of Polyacrylonitrile

Szabó

Tasi²,

Gaona³

et al. 2023

Front. Nucl. Eng.

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The uptake of 63Ni(II), 152Eu(III) and 242Pu(III/IV) by hardened cement paste (HCP, CEM I) in the degradation stage II (pH ≈ 12.5 [Ca] ≈ 0.02 M) was investigated in the absence and presence of α-hydroxyisobutyric, 3-hydroxybutyric and glutaric acids. These organic ligands were previously identified as proxies for the degradation products of UP2W (a polyacrylonitrile-based material used as filter aid in nuclear power plants) under repository conditions. Sorption experiments were conducted with various ligand concentrations (10−4 M ≤ [L]tot ≤ 0.1 M) and solid-to-liquid ratios (0.5 g⋅dm–3 ≤ S:L ≤ 20 g⋅dm–3). Redox conditions in the Pu systems were buffered with either hydroquinone (HQ, pe + pH ≈ 10) or Sn(II) (pe + pH ≈ 2). Strong sorption is observed for 152Eu(III) and 242Pu(III/IV) in the absence of proxy ligands, with distribution coefficients (log Rd ≈ 2.2–4, with Rd in m3⋅kg–1) in line with data reported in the literature. No differences are observed for sorption experiments with Pu in HQ and Sn(II) systems. Lower Rd values are determined for 63Ni(II) (log Rd,Ni63 ≈ 0-1), consistently with previous studies. In combination with log Rd,Ni determined on the basis of the concentration of stable Ni(II) in pristine HCP and in cement porewater, values of the partition coefficient (α) close to 1 are determined. This suggests that the uptake of 63Ni is possibly driven by isotopic exchange with the complete species inventory of stable Ni present in pristine HCP, including Ni in solid phases and associated with surfaces, e.g., of C-S-H phases. The presence of proxy ligands has a negligible effect on the uptake of 152Eu(III) up to [L]tot = 0.1 M. A slight decrease in the distribution ratios for 63Ni(II) and 242Pu(III/IV) is observed at [L]tot > 10−2 M, although the effect is less evident in the case of plutonium due to the dispersion of the data and the increase of the detection limits with increasing ligand concentrations. Compared to strongly complexing ligands like isosaccharinic acid or gluconate, the investigated proxy ligands show a minor capacity for radionuclide mobilization in cementitious systems, even at high concentrations.

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Section: Resultssupporting

confidence: 92%

Section: Introductionsupporting

confidence: 63%

Section: Cement and Cement Porewatermentioning

confidence: 99%

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Uptake of Ni(II), Eu(III) and Pu(III/IV) by Hardened Cement Paste in the Presence of Proxy Ligands for the Degradation of Polyacrylonitrile

Szabó

Tasi²,

Gaona³

et al. 2023

Front. Nucl. Eng.

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“…No thermodynamic studies are available in the literature dealing with the complexation of HIBA and HBA with Ca in hyperalkaline pH conditions. However, our previous undersaturation solubility experiments with Ca(OH) 2 (cr) in the presence of HIBA and HBA at 10 −6 M ≤ [L] tot ≤ 0.1 M confirmed that CaL complexes involving the deprotonation of the alcohol group are either very weak or not forming at all (Szabo et al, 2022).…”

Section: Comparison With Sorption Data Available In the Literaturementioning

confidence: 90%

“…The impact of the UP2W degradation products on the solubility and sorption of radionuclides in cementitious systems has been previously investigated in a number of experimental studies (Dario et al, 2004;Holgersson et al, 2011;Duro et al, 2012;Szabo et al, 2022). However, no information is available so far on the interaction of these degradation products with hardened cement paste (HCP), and their possible impact on the surface properties of the latter material.…”

Section: Introductionmentioning

confidence: 99%

Uptake of selected organic ligands by hardened cement paste: Studies on proxy ligands for the degradation of polyacrylonitrile and general considerations on the role of different functionalities in the uptake process

Szabó

Tasi²,

Gaona³

et al. 2022

Front. Nucl. Eng.

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The uptake of α-hydroxyisobutyric acid (HIBA), 3-hydroxybutyric acid (HBA) and glutaric acid (GTA) by hardened cement paste (HCP) in the degradation stage II was investigated at various ligand concentrations (10−7 M ≤ [L]tot ≤ 0.1 M) and solid-to-liquid ratios (0.2 g⋅dm−3 ≤ S:L ≤ 50 g⋅dm−3). These organic ligands were previously identified as representative of the main degradation products of UP2W, a polyacrylonitrile-based material used as filter aid in nuclear power plants, under repository conditions. Sorption experiments were conducted with inactive (HIBA, HBA, GTA) and active (14C-labelled GTA) organic ligands. Sorption experiments show a weak uptake of HIBA and HBA by HCP, with distribution coefficients determined as Rd (HIBA) = (2.2 ± 1.3)⋅10−3 m3⋅kg−1 and Rd (HBA) = (1.6 ± 0.8)⋅10−3 m3⋅kg−1. A stronger uptake is observed for GTA, i.e. Rd (GTA) = (1.3 ± 0.5)⋅10−2 m3⋅kg−1, likely reflecting the contribution from the ligand’s second carboxylate group. GTA follows a linear sorption behaviour within 10−7 M ≤ [GTA]tot ≤ 0.1 M, which was successfully modelled with a one-site Langmuir isotherm. The adsorption capacity determined for the uptake of GTA by HCP is slightly higher but in line with the capacity previously reported for isosaccharinic acid (ISA), whereas the affinity constant derived for GTA is significantly lower than values reported for stronger binding sites in HCP for the uptake of ISA. HIBA and HBA have a minor impact on the surface charge of HCP up to [L]tot ≈ 0.1 M. On the contrary, GTA induces a clear decrease in the surface charge above [GTA]tot ≈ 10−3 M resulting in an isoelectric point at [GTA]tot ≈ 6⋅10−2 M. Comparison of sorption data obtained in this work and reported in the literature for organic ligands containing the functional groups -COOH and -OH underlines the key role of multiple functionalities as a factor strengthening the interaction with the HCP surface. The participation of alcohol groups is particularly strong when present in their deprotonated state. These results provide information to quantitatively assess the uptake by HCP of organic ligands relevant in the context of nuclear waste disposal, and to understand their impact on the surface properties of cement.

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Degradation of the polyacrylonitrile-based UP2W material under cementitious conditions

Tasi,

Szabo,

Gaona

et al. 2024

Applied Geochemistry

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Solubility of Ca(ii), Ni(ii), Nd(iii) and Pu(iv) in the presence of proxy ligands for the degradation of polyacrylonitrile in cementitious systems

Abstract: The solubility of Ca(OH)2(cr), β-Ni(OH)2(cr), Nd(OH)3(s) and PuO2(ncr, hyd) was investigated in cement porewater solutions containing glutarate (GTA), a-hydroxyisobutarate (HIBA) and 3-hydroxybutarate (HBA). These ligands were proposed as probable degradation...

Cited by 5 publications

References 69 publications

Uptake of Ni(II), Eu(III) and Pu(III/IV) by Hardened Cement Paste in the Presence of Proxy Ligands for the Degradation of Polyacrylonitrile

Uptake of Ni(II), Eu(III) and Pu(III/IV) by Hardened Cement Paste in the Presence of Proxy Ligands for the Degradation of Polyacrylonitrile

Uptake of selected organic ligands by hardened cement paste: Studies on proxy ligands for the degradation of polyacrylonitrile and general considerations on the role of different functionalities in the uptake process

Degradation of the polyacrylonitrile-based UP2W material under cementitious conditions

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