The structure and composition of solid complexes comprising of Nd(III), Ca(II) and D-gluconate isolated from solutions relevant to radioactive waste disposal

Abstract

<jats:title>Abstract</jats:title><jats:p>Certain complexing agents (such as D-gluconate, D-isosaccharinate, etc.) as well as actinides and lanthanides are simultaneously present in cementitious radioactive waste repositories and (in the presence of water) are capable of forming complex compounds. Such processes may immobilize radionuclides and are of importance in the thermodynamic modelling of the aqueous chemistry of waste repositories. Nd(III) is considered to be a suitable model for trivalent lanthanides and actinides, due to the similarity of their ionic radii. In the current work, solid complexes isolated from aqueous solution containing Nd(III), Ca(II) and D-gluconate (Gluc<jats:sup>−</jats:sup>) were investigated. In an aqueous solution containing Nd(III) and Gluc<jats:sup>−</jats:sup>, the formation of a precipitate was observed at pH ≥ 8. This precipitate was found to redissolve around pH ~ 11, but reprecipitated when Ca(II) ions were added to the solution. In order to gain an insight in binary and ternary aqueous systems, in the present work we report the structure of these solid complexes obtained from XRD, FT-IR, Raman, SEM-EDAX and UV-DRS measurements. The structure of these solids, where possible, was compared with those identified in solution. The compositions of these complexes are suggested to be NdGlucH<jats:sub>−1</jats:sub>(OH) · 2H<jats:sub>2</jats:sub>O and CaNdGlucH<jats:sub>−1</jats:sub>(OH)<jats:sub>3</jats:sub> · 2H<jats:sub>2</jats:sub>O, respectively. In these, the chemical environment of the Nd(III) was found to be the same as that in the NdGlucH<jats:sub>−1</jats:sub>(OH)<jats:sup>0</jats:sup>(aq) solution species.</jats:p>

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

“…Böszörményi and co-workers recently reported the formation of Nd( iii )-gluconate solid phases Nd(GLU −H )(OH)·2H 2 O(cr) and CaNd(GLU −H )(OH) 3 ·2H 2 O(cr) in alkaline systems at room temperature. 81 These observations cannot be directly extrapolated to the proxy ligands investigated in this work because of (i) the stronger interaction of Nd( iii ) and gluconate in alkaline systems, 21,82 expectedly due to the presence of several alcohol groups in gluconate as opposed to HIBA and HBA (with only one OH-group each), and (ii) the large oversaturation conditions used by Böszörményi et al , i.e. [NdCl 3 ] 0 = [NaGLU] 0 = 0.5 M.…”

“…The formation of crystalline Ni(II) compounds with linear dicarboxylic acids is reported in the literature for the series oxalic, malonic, succinic and glutaric acids. [70][71][72][73][74][75][76][77][78] However, the synthetic routes used for the preparation of these solid phases usually rely on hydrothermal conditions and acidic environments to avoid the 81 These observations cannot be directly extrapolated to the proxy ligands investigated in this work because of (i) the stronger interaction of Nd(III) and gluconate in alkaline systems, 21,82 expectedly due to the presence of several alcohol groups in gluconate as opposed to HIBA and HBA (with only one OH-group each), and (ii) the large oversaturation conditions used by Böszörményi et al, i.e. [NdCl 3 ] 0 = [NaGLU] 0 = 0.5 M.…”

Formation of mono- and binuclear complexes of Nd3+ with d-gluconate ions in hyperalkaline solutions – Composition, equilibria and structure

“…Giroux et al reported that given the same conditions, precipitate also appears in the case of La 3+ , Eu 3+ , Dy 3+ , Er 3+ , and Lu 3+ ions around pH = 8 or at slightly higher pH when Gluc À is in excess [7]. In their study, seven complexes were described to form with all the five studied lanthanide cations: ML [26], and a precipitate appears at pH = 8, which was proven to have the composition of NdGlucH À1 OH in our previous work [27]. However, precipitation does not occur in the Nd 3+ -ÀGluc À system at pH > 12, which raises concerns of increased solubility since the complex formation was scarcely studied at pH higher than twelve [9,28], although this hyperalkaline medium [10] and high ionic strength (I = 5.3-7.4 M) [11] is inherent to radioactive depositories.…”

“…In accordance with our previous publication [25], precipitation occurs in the Nd 3+ -Glucsystem at pH > 8, but precipitation disappears at pH > 12 if the metal to ligand ratio is at least 1:2.5. The appearing precipitate was studied previously [27], and its composition was constant in the pH = 8 -12 range. Based on these data, potentiometric measurements were carried out in a reversed manner (titrating a pH % 13.5 sample with 1.0 M HCl (I = 4.5)) to reveal the interactions that take place in alkaline Nd 3+ -Glucsolutions.…”

Complex equilibria in strongly alkaline aqueous solutions containing Ca(II), Nd(III) and gluconate ions

“…The simultaneously obtained EDAX pictures show that Ca(II) and Nd(III) are evenly distributed (Figure 8). and Nd (right) of the ternary solid complex is shown 105 FT-IR spectra of the two complexes were compared to the spectra of Nd(OH)3, Ca-D-Gluconate and Na-D-Gluconate (Figure 9). The data obtained attest that Glucis present in both complexes, since the asymmetric and symmetric (indicated by * and + ) carboxylate peaks of Gluc -(1633 and 1398 cm −1 , respectively) appear in the spectrum of NdGlucH-1(OH)•2H2O (at 1664 cm −1 and at 1498 cm −1 ) and that of CaNdGlucH-1(OH)3•2H2O (at 1659 cm −1 and at 1500 cm −1 ).…”