A thermodynamical and structural study on the complexation of trivalent lanthanides with a polycarboxylate based concrete superplasticizer

Radiolysis effect on Eu(III)-superplasticiser interactions in artificial cement and squeezed cement pore waters

In the framework of the French deep geological repository for radioactive waste, cement-based materials are envisaged to immobilize radionuclides and/or provide protection from radiation to the environment. Superplasticisers (SPs) are added to these materials to increase their workability. SPs will undergo degradation by coupled radiolytic and hydrolytic effects in the pore solution leading to the formation of potentially complexing degradation products. The objective was to study the potential effect of radiolyzed superplasticizers contained in cement-based materials on radionuclide uptake. The Eu speciation and solubility with organic ligands resulting from the degradation of SPs were studied for the two solutions and the results were compared. Two different SPs were selected, a polycarboxylate ether and a polynapthalene sulfonate. Two different protocols were followed: direct irradiation of the solution containing the superplasticizer, and irradiation of the compacted cement sample followed by extraction of the pore water. Solubility enhancements observed in artificial cement waters are not representative of real cement pore water interactions, in agreement with other studies. Finally, the effects of alkaline hydrolysis and radiolysis of SPs on Eu solubility in pore water are limited.

Complexation of Np(V) with the Dicarboxylates, Malonate, and Succinate: Complex Stoichiometry, Thermodynamic Data, and Structural Information

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 β_n^°(Θ), Δ_rH_n^°, Δ_rS_n^°), near infrared absorption spectroscopy (vis/NIR) is applied. The complexation reactions are investigated as a function of the total concentration of malonate ([Mal^2-]_total) and succinate ([Succ^2-]_total), ionic strength [I_m = 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)_n^1-2n (n = 1, 2, L = Mal^2-, Succ^2-) is observed. With increasing temperature, the molar fractions of both complex species increase and the temperature-dependent conditional stability constants log β_n^'(Θ) at given ionic strengths are determined by the law of mass action. The log β_n^'(Θ) are extrapolated to IUPAC reference-state conditions (I_m = 0) according to the specific ion interaction theory (SIT), revealing thermodynamic log β_n^°(Θ) values. For all formed complexes, [NpO₂(Mal)^-: log β₁^°(25 °C) = 3.36 ± 0.11, NpO₂(Mal)₂^3-: log β₂^°(25 °C) = 3.95 ± 0.19, NpO₂(Succ)^-: log β₁^°(25 °C) = 2.05 ± 0.45, NpO₂(Succ)₂^3-: 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 β_n^°(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).

Solubilisation of Ni(II) and Eu(III) through complexation with a polyaryl ether based superplasticizer in alkaline media

Solubilisation of Ni(II) and Eu(III) by complexation with a polyaryl ether based superplasticizer (PAE SP) in alkaline solutions was studied. The solubilisation was investigated in two types of artificial cement pore waters simulating different stages of cement degradation at a pH of 12.4 and 13.3, respectively. The solubility of Ni(II) and Eu(III) increased as the concentration of superplasticizer was increased from 0.04 to 0.4 wt%. When the concentration of SP was increased from 0.4 to 4%, the solubility of Eu(III) and Ni(II) increased in the pore water with a pH of 12.4, while the concentrations decreased in the pore water with a pH of 13.3. This is explained by a more rapid degradation of the superplasticizer at higher pH leading to a release of phosphate groups and thereby precipitation of Eu(III) and Ni(II) as phosphates. Based on results of the solubilisation of Ni(II) and Eu(III) by model compounds (anisole and PEG 400) and ³¹P NMR spectroscopy it was confirmed that the complexation of the studied metals with the PAE polymer occurs via the phosphate group of the superplasticizer.

Influence of phosphate chelators on white efflorescence formation in dry fermented sausages with co-extruded alginate casings

The aim of the study was to investigate the effect of different condensed phosphates on the white efflorescence formation on dry fermented sausages with calcium alginate casings. The efflorescence formation is induced by the complexation of the divalent cations magnesium and calcium with lactate on the surface of the product. Phosphates are known to complex divalent cations like magnesium and calcium, which are responsible for the efflorescence formation with lactate. To treat the surface of the raw fermented sausages a mixture of di- and polyphosphates and a polyphosphate were used. The sausages were dipped in 5% solutions of the phosphates. The mixture of di- and polyphosphate showed the best results in reducing the white efflorescence formation, the amount of efflorescences on the surface was 18.12% after 8 weeks of storage. The diffusion of magnesium was significantly reduced by ~40% after 8 weeks of storage compared to the control for both phosphates. However, the crystals formed during storage had a different structure and size compared to the control. Isothermal titration calorimetry measurements showed that the divalent calcium ions and the polyphosphates from aggregates caused the crystal formation on the surface, whereas this effect was not seen in combination with magnesium. The surface treatment with the phosphates did not inhibit the white efflorescence formation. However, the extent was reduced but different kind of crystals were formed on the surface during the storage.

A spectroscopic study of the complexation reaction of trivalent lanthanides with a synthetic acrylate based PCE-superplasticizer

The interaction between different trivalent lanthanides and a synthetic acrylate based PCE-superplasticizer (52IPEG4.5) is investigated by using a combination of laser- and synchrotron based spectroscopic techniques. Time-resolved laser fluorescence spectroscopy (TRLFS) is used to obtain thermodynamic data (stability constants (log β'(T)), reaction enthalpy (Δ_rH) and entropy(Δ_rS)) of the complexation reaction of Eu(III) and 52IPEG4.5 as a function of the temperature (20-80 °C) and ligand concentration (<2 g/kg) in 0.1 mol/kg NaCl solution. Under the chosen experimental conditions, the increase in temperature mainly affects the complexation properties (loading capacity) of the macromolecule itself rather than the stability constant of the formed complex (log β'(T) ranging between 6.5 and 5.9). The thermodynamic results are complemented by extended X-ray absorption fine structure (EXAFS) spectroscopic measurements to resolve the molecular structure of 52IPEG4.5 complexes with Eu(III), Gd(III), and Tb(III). The results show, that each metal ion is coordinated by three carboxylic groups within the 52IPEG4.5 complexes. Furthermore, the determined interatomic distances exhibit that the functional groups are attached in a bidentate end-on fashion.