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Maiwald MM, Müller K, Heim K, Rothe J, Dardenne K, Rossberg A, Koke C, Trumm M, Skerencak-Frech A, Panak PJ. Complexation of Np(V) with the Dicarboxylates, Malonate, and Succinate: Complex Stoichiometry, Thermodynamic Data, and Structural Information. Inorg Chem 2021; 60:18674-18686. [PMID: 34821502 DOI: 10.1021/acs.inorgchem.1c01966] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The complexation of Np(V) with malonate and succinate is studied by different spectroscopic techniques, namely, attenuated total reflection Fourier transform infrared (ATR FT-IR) and extended X-ray absorption fine-structure (EXAFS) spectroscopy, as well as by quantum chemistry to determine the speciation, thermodynamic data, and structural information of the formed complexes. For complex stoichiometries and the thermodynamic functions (log βn°(Θ), ΔrHn°, ΔrSn°), near infrared absorption spectroscopy (vis/NIR) is applied. The complexation reactions are investigated as a function of the total concentration of malonate ([Mal2-]total) and succinate ([Succ2-]total), ionic strength [Im = 0.5-4.0 mol kg-1 Na+(Cl-/ClO4-)], and temperature (Θ = 20-85 °C). Besides the solvated NpO2+ ion, the formation of two Np(V) species with the stoichiometry NpO2(L)n1-2n (n = 1, 2, L = Mal2-, Succ2-) is observed. With increasing temperature, the molar fractions of both complex species increase and the temperature-dependent conditional stability constants log βn'(Θ) at given ionic strengths are determined by the law of mass action. The log βn'(Θ) are extrapolated to IUPAC reference-state conditions (Im = 0) according to the specific ion interaction theory (SIT), revealing thermodynamic log βn°(Θ) values. For all formed complexes, [NpO2(Mal)-: log β1°(25 °C) = 3.36 ± 0.11, NpO2(Mal)23-: log β2°(25 °C) = 3.95 ± 0.19, NpO2(Succ)-: log β1°(25 °C) = 2.05 ± 0.45, NpO2(Succ)23-: log β2°(25 °C) = 0.75 ± 1.22], an increase of the stability constants with increasing temperature was observed. This confirmed an endothermic complexation reaction. The temperature dependence of the log βn°(T) values is described by the integrated Van't Hoff equation, and the standard reaction enthalpies and entropies for the complexation reactions are determined. Furthermore, the sum of the specific binary ion-ion interaction coefficients Δεn°(Θ) for the complexation reactions are obtained as a function of the t from the respective SIT modeling as a function of the temperature. In addition to the thermodynamic data, the structures of the complexes and the coordination modes of malonate and succinate are investigated using EXAFS spectroscopy, ATR-FT-IR spectroscopy, and quantum chemical calculations. The results show that in the case of malonate, six-membered chelate complexes are formed, whereas for succinate, seven-membered rings form. The latter ones are energetically unfavorable due to the limited space in the equatorial plane of the Np(V) ion (as NpO2+ cation).
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Affiliation(s)
- Martin M Maiwald
- Ruprecht Karls Universität Heidelberg, Physikalisch-Chemisches Institut, Im Neuenheimer Feld 253, 69120 Heidelberg, Germany.,Karlsruher Institut für Technologie (KIT), Institut für Nukleare Entsorgung (INE), 76344 Eggenstein-Leopoldshafen, Germany
| | - Katharina Müller
- Helmholtz-Zentrum Dresden-Rossendorf, Institut für Ressourcenökologie, Bautzner Landstraße 400, 01328 Dresden, Germany
| | - Karsten Heim
- Helmholtz-Zentrum Dresden-Rossendorf, Institut für Ressourcenökologie, Bautzner Landstraße 400, 01328 Dresden, Germany
| | - Jörg Rothe
- Karlsruher Institut für Technologie (KIT), Institut für Nukleare Entsorgung (INE), 76344 Eggenstein-Leopoldshafen, Germany
| | - Kathy Dardenne
- Karlsruher Institut für Technologie (KIT), Institut für Nukleare Entsorgung (INE), 76344 Eggenstein-Leopoldshafen, Germany
| | - André Rossberg
- Helmholtz-Zentrum Dresden-Rossendorf, Institut für Ressourcenökologie, Bautzner Landstraße 400, 01328 Dresden, Germany
| | - Carsten Koke
- Ruprecht Karls Universität Heidelberg, Physikalisch-Chemisches Institut, Im Neuenheimer Feld 253, 69120 Heidelberg, Germany
| | - Michael Trumm
- Karlsruher Institut für Technologie (KIT), Institut für Nukleare Entsorgung (INE), 76344 Eggenstein-Leopoldshafen, Germany
| | - Andrej Skerencak-Frech
- Karlsruher Institut für Technologie (KIT), Institut für Nukleare Entsorgung (INE), 76344 Eggenstein-Leopoldshafen, Germany
| | - Petra J Panak
- Ruprecht Karls Universität Heidelberg, Physikalisch-Chemisches Institut, Im Neuenheimer Feld 253, 69120 Heidelberg, Germany.,Karlsruher Institut für Technologie (KIT), Institut für Nukleare Entsorgung (INE), 76344 Eggenstein-Leopoldshafen, Germany
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Adam N, Hinz K, Gaona X, Panak PJ, Altmaier M. Impact of selected cement additives and model compounds on the solubility of Nd(III), Th(IV) and U(VI): screening experiments in alkaline NaCl, MgCl2 and CaCl2 solutions at elevated ionic strength. RADIOCHIM ACTA 2021. [DOI: 10.1515/ract-2021-1010] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Abstract
The solubility of Nd(III), Th(IV) and U(VI) was studied from undersaturation conditions in the presence of selected organic cement additives and model compounds: adipic acid, methyl acrylate, citric acid, melamine, ethylene glycol, phthalic acid and gluconic acid. Experiments were performed under Ar atmosphere in NaCl (2.5 and 5.0 M), MgCl2 (1.0 and 3.5 M) and CaCl2 (1.0 and 3.5 M) solutions with 9 ≤ pHm ≤ 13 (pHm = −log[H+]). Initial concentrations of organic ligands in solution were set constant in all systems to [L]0 = 0.025 M, except in specific cases (e.g. adipic acid, melamine and phthalic acid) where the ligand concentration in the matrix solutions was lower and controlled by solubility. Adipic acid, methyl acrylate, melamine, ethylene glycol and phthalic acid do not impact the solubility of Nd(III), Th(IV) and U(VI) in the investigated NaCl, MgCl2 and CaCl2 systems. Citrate significantly enhances the solubility of Nd(III), Th(IV) and U(VI) in NaCl systems. A similar effect was observed for Th(IV) and U(VI) in the presence of gluconate in NaCl systems. The impact of pH on the stability of the complexes is different for both ligands. Because of the larger number of alcohol groups in the gluconate molecule, this ligand is prone to form more stable complexes under hyperalkaline conditions that likely involve the deprotonation of several alcohol groups. The complexation of gluconate with U(VI) at pHm ≈ 13 is however weaker than at pHm ≈ 9 due to the competition with the highly hydrolysed moiety prevailing at pHm ≈ 13, i.e. UO2(OH)4
2−. The impact of citrate and gluconate in MgCl2 and CaCl2 systems is generally weaker than in NaCl systems, expectedly due to the competition with binary Mg-L and Ca-L complexes. However, the possible formation of ternary complexes further enhancing the solubility is hinted for the systems Mg/Ca-Th(IV)-GLU and Ca-U(VI)-GLU. These observations reflect again the differences in the complexation properties of citrate and gluconate, the key role of the alcohol groups present in the latter ligand, and the importances of interacting matrix cations. The screening experiments conducted within this study contribute to the identification of organic cement additives and model compounds potentially impacting the solution chemistry of An(III)/Ln(III), An(IV) and An(VI) under intermediate to high ionic strength conditions (2.5 ≤ I ≤ 10.5 M). This shows evident differences with respect to investigations conducted in dilute systems, and thus represents a very relevant input in the safety assessment of repositories for radioactive waste disposal where such elevated ionic strength conditions are expected.
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Affiliation(s)
- Nicole Adam
- Karlsruhe Institute of Technology (KIT), Campus North, Institute for Nuclear Waste Disposal (INE) , P.O. Box 3640 , 76021 Karlsruhe , Germany
| | - Katja Hinz
- Institute of Physical Chemistry, University of Heidelberg , Im Neuenheimer Feld 253 , 69120 Heidelberg , Germany
| | - Xavier Gaona
- Karlsruhe Institute of Technology (KIT), Campus North, Institute for Nuclear Waste Disposal (INE) , P.O. Box 3640 , 76021 Karlsruhe , Germany
| | - Petra J. Panak
- Karlsruhe Institute of Technology (KIT), Campus North, Institute for Nuclear Waste Disposal (INE) , P.O. Box 3640 , 76021 Karlsruhe , Germany
- Institute of Physical Chemistry, University of Heidelberg , Im Neuenheimer Feld 253 , 69120 Heidelberg , Germany
| | - Marcus Altmaier
- Karlsruhe Institute of Technology (KIT), Campus North, Institute for Nuclear Waste Disposal (INE) , P.O. Box 3640 , 76021 Karlsruhe , Germany
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Maiwald MM, Trumm M, Dardenne K, Rothe J, Skerencak-Frech A, Panak PJ. Speciation, thermodynamics and structure of Np(V) oxalate complexes in aqueous solution. Dalton Trans 2020; 49:13359-13371. [PMID: 32955047 DOI: 10.1039/d0dt02379e] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The speciation, thermodynamics and structure of the Np(v) (as the NpO2+ cation) complexes with oxalate (Ox2-) are studied by different spectroscopic techniques. Near infrared absorption spectroscopy (Vis/NIR) is used to investigate complexation reactions as a function of the total ligand concentration ([Ox2-]total), ionic strength (Im = 0.5-4.0 mol kg-1 Na+(Cl-/ClO4-)) and temperature (T = 20-85 °C) for determination of the complex stoichiometry and thermodynamic functions (log β0n(T), ΔrH0n, ΔrS0n). Besides the solvated NpO2+ ion, two NpO2+ oxalate species (NpO2(Ox)n1-2n; n = 1, 2) are identified. With increasing temperature a decrease of the molar fractions of the 1 : 1 - and 1 : 2 - complexes is observed. Application of the law of mass action yields the temperature dependent conditional stability constants log β'n(T) at a given ionic strength which are extrapolated to IUPAC reference state conditions (Im = 0) according to the specific ion interaction theory (SIT). The log β0n(T) values of both complex species (log β01(25 °C) = 4.53 ± 0.12; log β02(25 °C) = 6.22 ± 0.24) decrease with increasing temperature confirming an exothermic complexation reaction. The temperature dependence of the thermodynamic stability constants is described by the integrated van't Hoff equation yielding the standard reaction enthalpies (ΔrH01 = -1.3 ± 0.7 kJ mol-1; ΔrH02 = -8.7 ± 1.4 kJ mol-1) and entropies (ΔrS01 = 82 ± 2 J mol-1 K-1; ΔrS02 = 90 ± 5 J mol-1 K-1) for the complexation reactions. In addition, the sum of the specific binary ion-ion interaction coefficients Δε0n(T) for the complexation reactions are obtained from SIT modelling as a function of the temperature. The structure of the complexes and the coordination mode of oxalate are investigated using EXAFS spectroscopy and quantum chemical calculations. The results show, that in case of both species NpO2(Ox)- and NpO2(Ox)23-, chelate complexes with 5-membered rings are formed.
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Affiliation(s)
- M M Maiwald
- Ruprecht Karls Universität Heidelberg, Physikalisch-Chemisches Institut, Im Neuenheimer Feld 253, D-69120 Heidelberg, Germany.
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Maiwald MM, Dardenne K, Rothe J, Skerencak-Frech A, Panak PJ. Thermodynamics and Structure of Neptunium(V) Complexes with Formate. Spectroscopic and Theoretical Study. Inorg Chem 2020; 59:6067-6077. [PMID: 32282193 DOI: 10.1021/acs.inorgchem.0c00054] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The temperature and ionic strength dependences of the complex formation of NpO2+ with formate in aqueous solution are studied by absorption spectroscopy (Im = 0.5-4.0 mol kg-1, T = 20-85 °C, [Form-]total = 0-0.65 mol kg-1), extended X-ray absorption fine structure spectroscopy (EXAFS) and quantum chemical methods. The complex stoichiometry and the thermodynamic functions of the complexation reactions are determined by peak deconvolution of the absorption spectra and slope analyses. Besides the solvated NpO2+ ion, two NpO2+ formate species (NpO2(Form)n1-n; n = 1, 2) are identified. Application of the law of mass action yields the temperature dependent conditional stability constants log β'n(T) at a given ionic strength. These data are extrapolated to IUPAC reference state conditions (Im = 0) using the specific ion interaction theory (SIT). The results show, that log β01(20 °C) = 0.67 ± 0.04 decreases by approximately 0.1 logarithmic units with increasing temperature, log β02(20 °C) = 0.11 ± 0.11 increases by about 0.2 logarithmic units. The temperature dependence of the log β0n(T) values is modeled with the integrated Van't Hoff equation yielding the standard reaction enthalpy ΔrH0 and entropy ΔrS0 of the complexation reactions. The results show that the formation of NpO2(Form) is exothermic (ΔrH01 = -2.8 ± 0.9 kJ mol-1) whereas the formation of NpO2(Form)2- is endothermic (ΔrH02 = 6.7 ± 4.1 kJ mol-1). Furthermore, the binary ion-ion interaction coefficients εT(i,k) of the formed complexes are determined in NaClO4 and NaCl media as a function of the temperature. The coordination mode of formate toward the metal ion is investigated by EXAFS spectroscopy and quantum chemical calculations. A coordination of the ligand via only one O atom of formate to the metal ion is identified.
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Affiliation(s)
- Martin M Maiwald
- Physikalisch-Chemisches Institut, Ruprecht Karls Universität Heidelberg, Im Neuenheimer Feld 253, D-69120 Heidelberg, Germany
| | - Kathy Dardenne
- Institut für Nukleare Entsorgung (INE), Karlsruher Institut für Technologie (KIT), D-76344 Eggenstein-Leopoldshafen, Germany
| | - Jörg Rothe
- Institut für Nukleare Entsorgung (INE), Karlsruher Institut für Technologie (KIT), D-76344 Eggenstein-Leopoldshafen, Germany
| | - Andrej Skerencak-Frech
- Institut für Nukleare Entsorgung (INE), Karlsruher Institut für Technologie (KIT), D-76344 Eggenstein-Leopoldshafen, Germany
| | - Petra J Panak
- Physikalisch-Chemisches Institut, Ruprecht Karls Universität Heidelberg, Im Neuenheimer Feld 253, D-69120 Heidelberg, Germany.,Institut für Nukleare Entsorgung (INE), Karlsruher Institut für Technologie (KIT), D-76344 Eggenstein-Leopoldshafen, Germany
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Baumann A, Yalçıntaş E, Gaona X, Polly R, Dardenne K, Prüßmann T, Rothe J, Altmaier M, Geckeis H. Thermodynamic description of Tc(iv) solubility and carbonate complexation in alkaline NaHCO3–Na2CO3–NaCl systems. Dalton Trans 2018; 47:4377-4392. [DOI: 10.1039/c8dt00250a] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A comprehensive thermodynamic model is derived for the system Tc4+–Na+–Cl−–OH−–HCO3−–CO32−–H2O(l) based upon solubility experiments in alkaline carbonate solutions, advanced spectroscopic techniques and DFT calculations.
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Affiliation(s)
- A. Baumann
- Institute for Nuclear Waste Disposal
- Karlsruhe Institute of Technology
- 76021 Karlsruhe
- Germany
| | - E. Yalçıntaş
- Institute for Nuclear Waste Disposal
- Karlsruhe Institute of Technology
- 76021 Karlsruhe
- Germany
- Los Alamos National Laboratory
| | - X. Gaona
- Institute for Nuclear Waste Disposal
- Karlsruhe Institute of Technology
- 76021 Karlsruhe
- Germany
| | - R. Polly
- Institute for Nuclear Waste Disposal
- Karlsruhe Institute of Technology
- 76021 Karlsruhe
- Germany
| | - K. Dardenne
- Institute for Nuclear Waste Disposal
- Karlsruhe Institute of Technology
- 76021 Karlsruhe
- Germany
| | - T. Prüßmann
- Institute for Nuclear Waste Disposal
- Karlsruhe Institute of Technology
- 76021 Karlsruhe
- Germany
| | - J. Rothe
- Institute for Nuclear Waste Disposal
- Karlsruhe Institute of Technology
- 76021 Karlsruhe
- Germany
| | - M. Altmaier
- Institute for Nuclear Waste Disposal
- Karlsruhe Institute of Technology
- 76021 Karlsruhe
- Germany
| | - H. Geckeis
- Institute for Nuclear Waste Disposal
- Karlsruhe Institute of Technology
- 76021 Karlsruhe
- Germany
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