Sr2+ Sorption and leach rate studies on synthetic calcium silicate hydroxy hydrate

Synthetic calcium silicate hydroxy hydrate, which is identical to unsubstituted and substituted 1.1-nm tobermorite mineral, has the capacity to pickup selectivity Sr²⁺ cation from mixed cationic solutions in the presence of 1,000 times concentrations of Na⁺, K⁺, Ca²⁺, Mg²⁺, and Ba²⁺. The selective uptake of Sr²⁺ from mixed cationic solutions and simulated intermediate level waste (ILW) solutions has been quantified as distribution coefficient (K_d) and decontamination factors (Df). The sorption studies have been performed by analysis of Sr²⁺ in solution both by atomic absorption spectrophotometry and radiometric measurements. The proportional depletion of β activity from strontium solutions labeled with isotope Sr⁹⁰ has been utilized to study the concentration and mass dependence of the Sr²⁺ uptake by the exchanger. Kielland coefficient at 25°C have been determined from the isotherms plotted for the Sr²⁺ ⇌ Ca²⁺ system. Leach rate studies on the blocks made from ordinary portland cement (OPC) + tobermorite admixtures show that the release rate of Sr²⁺ from cement matrix is drastically lowered when the additive is increased. By using 40 wt% Al-substituted tobermorite as an additive to OPC, we found that it was possible to fix about 77% of Sr in cement matrix against 17% fixation in the OPC.     

Adaptive Neuro-Fuzzy inference system analysis on sorption studies of strontium and cesium cations onto a novel impregnated nano-zeolite

In this research, a novel impregnated nano-zeolite (NAASMS-Z) was synthesized and characterized using different characterization techniques. Excellent properties, such as high specific surface area (~502.77 m²/g), low pore size (~8.92 Å) and the existence of numerous functional groups caused the efficient elimination of Sr²⁺ and Cs⁺ cations from aquatic systems. The sorption performance of the nano-particles was enhanced by impregnation up to 60% in the aquatic media. The kinetic study indicated that the elimination process of both the concerned cations is controlled by external film mass transfer through the boundary within the first 30 min then controlled by intra-particle diffusion. The sorption equilibrium data suggested that the sorption process occurs on the heterogeneous sorbent surface. Parameters affecting the elimination of Sr²⁺ and Cs⁺ from a single metal sorption system, such as pH, initial contaminant concentration (C_i) and contact time (t), were investigated and optimized. A predictive model based on an Adaptive Neuro-Fuzzy Inference system (ANFIS) analysis was applied to evaluate the experimental parameters affecting the elimination of Sr²⁺ and Cs⁺ cations from aquatic system. A Mamdani-type FIS was employed to justify a collection of 16 rules (If-Then format) by means of centroid membership functions. The suggested fuzzy model revealed high predictive concert with high correlation coefficient (R²) and satisfactory deviation from the experimental data, affirming its appropriateness to predict Sr²⁺ and Cs⁺ elimination efficacy from the studied system. Rooted in experimental data and statistical analysis, the synthetized material was effective for treating contaminated aquatic solutions containing Sr²⁺ and Cs⁺ cations.     

Efficient Co-Adsorption and Highly Selective Separation of Cs+ and Sr2+ with a K+-Activated Niobium Germanate by the pH Control

¹³⁷Cs and ⁹⁰Sr are hazardous to ecological environment and human health due to their strong radioactivity, long half-life, and high mobility. However, effective adsorption and separation of Cs⁺ and Sr²⁺ from acidic radioactive wastewater is challenging due to stability issues of material and the strong competition of protons. Herein, a K⁺-activated niobium germanate (K-NGH-1) presents efficient Cs⁺/Sr²⁺ coadsorption and highly selective Cs⁺/Sr²⁺ separation, respectively, under different acidity conditions. In neutral solution, K-NGH-1 exhibits ultrafast adsorption kinetics and high adsorption capacity for both Cs⁺ and Sr²⁺ (q_m^Cs = 182.91 mg g⁻¹; q_m^Sr = 41.62 mg g⁻¹). In 1 M HNO₃ solution, K-NGH-1 still possesses q_m^Cs of 91.40 mg g⁻¹ for Cs⁺ but almost no adsorption for Sr²⁺. Moreover, K-NGH-1 can effectively separate Cs⁺ from 1 M HNO₃ solutions with excess competing Sr²⁺ and Mⁿ⁺ (Mⁿ⁺ = Na⁺, Ca²⁺, Mg²⁺) ions. Thus, efficient separation of Cs⁺ and Sr²⁺ is realized under acidic conditions. Besides, K-NGH-1 shows excellent acid and radiation resistance and recyclability. All the merits above endow K-NGH-1 with the first example of niobium germanates for radionuclides remediation. This work highlights the facile pH control approach towards bifunctional ion exchangers for efficient Cs⁺/Sr²⁺ coadsorption and selective separation.     

Effect of compositional variations on charge compensation of AlO4 and BO4 entities and on crystallization tendency of a rare-earth-rich aluminoborosilicate glass

This paper presents the structural and crystallization study of a rare-earth-rich aluminoborosilicate glass that is a simplified version of a new nuclear glass proven to be a potential candidate for the immobilization of highly concentrated radioactive wastes that will be produced in the future. In this work, we studied the impact of changing the nature of alkali (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺) or alkaline-earth (Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺) cations present in glass composition on glass structure (by ²⁷Al and ¹¹B nuclear magnetic resonance spectroscopy) and on its crystallization tendency during melt cooling at 1 K/min (average cooling rate during industrial process). From these composition changes, it was established that alkali cations were preferentially involved in charge compensation of (AlO₄)⁻ and (BO₄)⁻ entities in the glassy network comparatively to alkaline-earth cations. Whatever the nature of alkali cations, glass compositions containing calcium gave way to the crystallization of an apatite silicate phase bearing calcium and rare-earth (RE) cations (Ca₂RE₈(SiO₄)₆O₂, RE = Nd or La) but melt crystallization tendency during cooling strongly varied with the nature of alkaline-earth cations.     

The fabrication and properties of Zr-O-F ceramics for the immobilization of Zircaloy nuclear waste

The hot-pressing behaviour of hydrated zirconium oxide (with fluoride) derived from Zircaloy nuclear waste is described. The material densifies at relatively low temperatures to give a crystalline ceramic with monoclinic ZrO₂ and an oxyfluoride (Zr₁₀O₁₃F₁₄) as major phases. Doping with the inactive radwaste ions U⁴⁺, Sr²⁺ and Cs⁺ has shown that these should be taken into solid solution in the ceramic at the levels at which they are likely to be present in actual waste. Dissolution tests are described which establish that the ceramics are resistant to attack by water and hence should provide suitable leachresistant hosts for the immobilization of the radwaste ions.     

Sorption of caesium,strontium and europium ions on clay minerals

Batch experiments have been performed to study the sorption and transport properties of Cs⁺, Sr²⁺ and Eu³⁺ on different clay minerals already established to be predominantly kaolinite and montmorillonite. The uptake of these radionuclides increases in the order Cs相似文献   

Direct Separation of UO22+ by Coordination Sieve Effect via Spherical Coordination Traps

Molecule sieve effect (MSE) can enable direct separation of target, thus overcoming two major scientific and industrial separation problems in traditional separation, coadsorption, and desorption. Inspired by this, herein, the concept of coordination sieve effect (CSE) for direct separation of UO₂²⁺, different from the previously established two-step separation method, adsorption plus desorption is reported. The used adsorbent, polyhedron-based hydrogen-bond framework (P-HOF-1), made from a metal–organic framework (MOF) precursor through a two-step postmodification approach, afforded high uptake capacity (close to theoretical value) towards monovalent Cs⁺, divalent Sr²⁺, trivalent Eu³⁺, and tetravalent Th⁴⁺ ions, but completely excluded UO₂²⁺ ion, suggesting excellent CSE. Direct separation of UO₂²⁺ can be achieved from a mixed solution containing Cs⁺, Sr²⁺, Eu³⁺, Th⁴⁺, and UO₂²⁺ ions, giving >99.9% removal efficiency for Cs⁺, Sr²⁺, Eu³⁺, and Th⁴⁺ ions, but <1.2% removal efficiency for UO₂²⁺, affording benchmark reverse selectivity (S_M/U) of >83 and direct generation of high purity UO₂²⁺ (>99.9%). The mechanism for such direct separation via CSE, as unveiled by both single crystal X-ray diffraction and density-functional theory (DFT) calculation, is due to the spherical coordination trap in P-HOF-1 that can exactly accommodate the spherical coordination ions of Cs⁺, Sr²⁺, Eu³⁺, and Th⁴⁺, but excludes the planar coordination UO₂²⁺ ion.     

Influence of the concentrations of potassium, sodium, and ammonium ions on the cesium sorption with mixed nickel potassium ferrocyanide sorbent based on hydrated titanium dioxide

The effect of single-charged cations (Na⁺, K⁺, NH ₄ ⁺ ) on the cesium sorption with mixed nickel potassium ferrocyanide sorbent based on hydrated TiO₂ was studied. The K⁺ and Na⁺ ions exert no effect at their concentrations of up to 0.5 M; the Cs⁺ distribution coefficients from KCl and NaCl solutions are (1.1 ± 0.5) × 10⁵ and (8 ± 3) × 10⁴ mL g^?1, respectively. The sorbent is highly specific to Cs⁺ in the presence of ammonium ions. The sorption mechanisms were studied. The concentration ranges in which Cs⁺ and NH ₄ ⁺ are sorbed by independent mechanisms (Cs⁺, by the ferrocyanide phase; NH ₄ ⁺ , by the phase of hydrated TiO₂) and in which the Cs⁺ distribution coefficient decreases owing to competitive filling of the ferrocyanide phase with ammonium ions were determined. At cesium concentrations in solution exceeding 50 mg L^?1, Cs⁺ and NH ₄ ⁺ are absorbed jointly owing to coprecipitation in the mixed ferrocyanide phase in the pore space of the sorbent.     

Synthesis and Structure of Mixed-Cation Salts with [PuO<Subscript>4</Subscript>(OH)<Subscript>2</Subscript>]<Superscript>3–</Superscript> Anions

Mixed-cation salts of the composition NaM₂[PuO₄(OH)₂]·4H₂O, where M = Rb (I) and Cs (III), and NaRb₅[PuO₄(OH)₂]₂·6H₂O (II) were synthesized and structurally characterized. The central Pu atom in [PuO₄(OH)₂]^3– anions has oxygen surrounding in the form of a tetragonal bipyramid with oxygen atoms of hydroxide ions in apical positions. The hydrated Na⁺ cations have oxygen surrounding in the form of a distorted octahedron. In the structure of I, there are two independent Rb⁺ cations with 10- and 12-vertex coordination polyhedra (CPs), and in the structure of II, three independent Rb⁺ cations with the 12-, 11-, and 13-vertex CPs. In the structure of III, the Cs⁺ cation has a 12-vertex CP. Frameworks of large Rb⁺ or Cs⁺ cations can be distinguished in the structure. The CPs of the Pu and Na atoms (I, III) sharing a common edge or the isolated CPs of the Pu and Na atoms (II) are incorporated in these frameworks. Hydrogen bonds influence the crystal packing and the geometric characteristics of the [PuO₄(OH)₂]^3– anions.     

Synthesis, structure and ion exchange properties of 11 Å tobermorites from newsprint recycling residue

Al-substituted 11 Å tobermorites were obtained from stoichiometrically adjusted mixtures of newsprint recycling waste, sodium silicate and calcium oxide via hydrothermal synthesis at 100 °C. Hydrothermal processing in water yielded a highly crystalline 11 Å tobermorite product with a Cs⁺ cation exchange capacity of 85 meq 100 g⁻¹ and selective Cs⁺ distribution coefficient of ∼5500 cm³ g⁻¹. Conversely, a product of inferior crystallinity was obtained from hydrothermal synthesis in alkaline liquor whose Cs⁺ ion exchange capacity and selective Cs⁺ distribution coefficient were found to be 66.3 meq 100 g⁻¹ and ∼700 cm³ g⁻¹, respectively. Silicate chain configuration was found to have a modest impact on the number of cation exchange sites per unit cell, whereas the influence of structural defects on selectivity was more pronounced. The structures and ion exchange credentials of both 11 Å tobermorite products corresponded well with those of their essentially phase-pure counterparts.     

Synthesis of nuclear waste monazites,ideal actinide hosts for geologic disposal

Monazite, an orthophosphate mineral of the lanthanides (Ln) and the actinides (An) U and Th, is a model for an ideal synthetic mineral waste form for geologic disposal of long-lived nuclear waste actinides. Natural monazites are known to have survived many of the conditions that might be inflicted on a nuclear waste repository by geological disruptions. High Th and U monazites with compositions typical of nuclear wastes have been synthesized with a routine calcination-pelletization-crystallization procedure. Charge balance for the Th⁴⁺ → Ln³⁺ substitution can be provided by either an equimolar Ca²⁺ → Ln³⁺ or Si⁴⁺ → P⁵⁺ substitution. For U⁴⁺ → Ln³⁺, only the Ca²⁺ → Ln³⁺ substitution resulted in a phase-pure monazite. Unit cell parameter data were obtained for each nuclear waste monazite phase.     

Adsorption behavior of iodide ion by silver-doped zeolite 4A in LiCl-KCl molten salt

In this study, the porous material zeolite with cage-like structure was modified to prepare silver-doped zeolite 4A (abbreviated as Ag@4A) using ion exchange method, with a silver loading of 34.2 wt% and a specific surface area of ??23.62 m²/g. The adsorption performance of Ag@4A for anionic iodine in LiCl-KCl molten salt system was investigated through static adsorption experiments. The modified adsorbents and experimental samples were analyzed by XRD, SEM, ICP-OES and other methods. At 550 °C, compared with the unmodified zeolite 4A, adsorption capacity of 34 mg/g of iodine, the maximum adsorption capacity of Ag@4A for iodine ions was up to 160 mg/g. When Cs⁺ existed in the system, the maximum adsorption capacity of Ag@4A for iodide ions was about 64 mg/g; when Cs⁺ and Sr²⁺ coexisted, the maximum adsorption capacity of Ag@4A for iodide ions decreased to 103 mg/g. Ag@4A also showed a certain adsorption capacity for Cs⁺ and Sr²⁺. These results indicated that the Ag@4A has potential application for the removal of iodide ions and other cations in chloride molten salt.     

Ion-selective properties of metastable (VO)<Subscript>0.09</Subscript>V<Subscript>0.18</Subscript>Mo<Subscript>0.82</Subscript>O<Subscript>3</Subscript> · 0.54H<Subscript>2</Subscript>O

This paper describes a thin-film solid electrode with an ion-sensitive membrane based on the mixed oxide (VO)_0.09V_0.18Mo_0.82O₃ · 0.54H₂O. The electrode is selective for tetravalent vanadium in the concentration range 3 ≤ pC _V ⁴⁺ ≤ 5 and acidity range 4.5 ≤ pH ≤ 6, with a slope close to the theoretical value. In the range 1 ≤ pH < 5, the electrode responds to changes in hydrogen ion concentration, with a slope of 50 ± 2 mV/pH. Its alkali-metal-ion response shows up in the range 1 ≤ pC _M ⁺ ≤ 4 for pH ≥ 6. We examine the effect of the Li⁺, K⁺, Na⁺, Cs⁺, Rb⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Co²⁺, Ni²⁺, Mn²⁺, Al³⁺, Cr³⁺, and VO₂⁺ ions on the potential of the electrode and determine its selectivity coefficients for these cations.     

Aspects of the in vitro bioactivity and antimicrobial properties of Ag+- and Zn2+-exchanged 11 Å tobermorites

11 Å tobermorite, Ca₅Si₆O₁₆(OH)₂ · 4H₂O, is a layer lattice ion exchange mineral whose potential as a carrier for Ag⁺ and Zn²⁺ ions in antimicrobial, bioactive formulations has not yet been explored. In view of this, the in vitro bioactivity of Ag⁺- and Zn²⁺-exchanged 11 Å tobermorites and their bactericidal action against S. aureus and P. aeruginosa are reported. The in vitro bioactivity of the synthetic unsubstituted tobermorite phase was confirmed by the formation of bone-like hydroxycarbonate apatite (HCA) on its surface within 48 h of contact with simulated body fluid. The substitution of labile Ag⁺ ions into the tobermorite lattice delayed the onset of HCA-formation to 72 h; whereas, the Zn²⁺-substituted phase failed to elicit an HCA-layer within 14 days. Both Ag⁺- and Zn²⁺-exchanged tobermorite phases were found to exhibit marked antimicrobial action against S. aureus and P. aeruginosa, two common pathogens in biomaterial-centred infections.     

Colorimetric and fluorescent sensing of transition metal ions in aqueous medium by salicylaldimine based chemosensor

The cation sensing property of highly sensitive chromogenic receptor N, N′-bis (salicylidine)-o-phenylene diamine (receptor 1) was studied by visual observation, UV–vis spectroscopy and fluorescence spectroscopy. The proposed study has been targeted to sense the first transition series metal cations like Fe³⁺, Co²⁺, Ni²⁺ and Cu²⁺. Binding affinity toward Cu²⁺ is found to be of higher magnitude compared to the other three cations mentioned. Receptor 1 on binding with Fe³⁺, Co²⁺ Ni²⁺ and Cu²⁺ ions shows fluorescence enhancement which is due to the inhibition of PET mechanism.     

In situ type study of hydrothermally prepared titanates and silicotitanates

One of the most vexing problems facing the nuclear industry and countries with nuclear weapons is the safe disposal of the generated nuclear waste. Huge quantities of nuclear waste arising from weapons manufacture are stored at the Hanford and Savannah River sites in the USA. The general method of remediation involves the removal of Cs-137, Sr-90 and actinides from a huge quantity of salts, principally NaNO₃, organics and complexing agents. It has been found that a sodium silicotitanate is able to remove Cs⁺ selectively from the waste and certain sodium titanates remove Sr²⁺ and actinides. These compounds have been prepared by ex-situ hydrothermal methods. We have studied the in situ growth of these materials at the National Synchrotron Light Source, Brookhaven National Laboratory. In addition we will describe the mechanism of ion exchange in the titanosilicate as observed by in situ methods and how the combination of these techniques coupled with an intimate knowledge of the structure of the solids is helping to solve the remediation process. In general, the in situ method allows the investigator to follow the nucleation and crystal growth or phase transformations occurring in hydrothermal reactions. An erratum to this article is available at .     

Complexes of An(VI) with Cyclobutanecarboxylic Acid Anions and Outer-Sphere Alkali Metal Cations

New complexes of hexavalent actinides with cyclobutanecarboxylic acid (Hcbc) anions, Na₄[NpO₂· (cbc)₃]₄·H₂O (I), K[NpO₂(cbc)₃] (II), Cs[NpO₂(cbc)₃] (III), and Cs[PuO₂(cbc)₃] (IV), cbc = C₄H₇(COO)^–, were synthesized and studied by single crystal X-ray diffraction. The structures of I–IV are based on the anionic complexes [AnO₂(cbc)₃]^– surrounded by alkali metal cations. The AnO ₂ ²⁺ cation in the anionic complex is bonded with three chelating C₄H₇COO^– anions, and the coordination polyhedron (CP) of An is a hexagonal bipyramid with the O atoms of the AnO ₂ ²⁺ cations in apical positions. The coordination number (CN) of the alkali metal cations in the structures of II–IV is the same and equal to 6; the coordination surrounding of the K⁺ and Cs⁺ cations is constituted by the O atoms of six C₄H₇COO^– anions. The crystal structures of II–IV are examples of cubic 3-connected networks (10,3) built of alkali metal and actinide cations. In the structure of I, there are four kinds of crystallographically different NpO ₂ ²⁺ and Na⁺ cations. The coordination surrounding of the NpO ₂ ²⁺ cations differs only in the conformational characteristics of the C₄H₇COO^– ligands. Four independent Na⁺ cations differ from each other in the structure of the coordination surrounding. The CPs of the Na(1) and Na(4) atoms can be described as distorted octahedra (CN 6); that of Na(3), as a trigonal prism (CN 6); and that of Na(2), as a tetragonal pyramid (CN 5) with one of the basal vertices occupied by the Ow(1) atom of a water molecule. In the structure of I, the configuration of the network formed by the Na and Np cations differs from the cubic 3-connected network found in the structures of II–IV.     

Behavior of Trace Amounts of Cd and Zn in Sorption and Coprecipitation in Tetrahydrofuran Solutions

Sorption of trace amounts of ¹⁰⁹Cd and ⁶⁵Zn on zeolites NaX and NaA in the presence of divalent lanthanides Ln²⁺ (Ln = Tm, Dy, Nd) from tetrahydrofuran (THF) solutions is studied. In contrast to ¹³⁷Cs⁺ and similar to ⁸⁵Sr²⁺, trace amounts of ¹⁰⁹Cd and ⁶⁵Zn are not practically sorbed on zeolites (about 99% of these radionuclides remains in the solution). The distribution coefficients K _d of ¹⁰⁹Cd and ⁶⁵Zn are ∼0.3 and ∼0.4 ml g⁻¹, respectively. In THF solutions, Tm²⁺ is oxidized to Tm³⁺, and TmI₃ ⋅ 3THF is precipitated. Study of cocrystallization of trace amounts of ¹⁰⁹Cd and ⁶⁵Zn and also of ⁸⁵Sr with this precipitate from THF solutions containing Tm²⁺ revealed that, in contrast to ⁸⁵Sr²⁺, ¹⁰⁹Cd and ⁶⁵Zn traces cocrystallize with the solid solvate phase. The cocrystallization coefficients D of ¹⁰⁹Cd and ⁶⁵Zn increase with increasing Tm³⁺/Tm²⁺ ratio in the solution. The mechanism suggested is that, in the presence of Tm²⁺, ¹⁰⁹Cd²⁺ and ⁶⁵Zn²⁺ are reduced to single-charged cations M⁺, which then rapidly react with the double-charged cations M²⁺ with the formation of dimers M ₂ ³⁺ (M = Cd, Zn).__________Translated from Radiokhimiya, Vol. 47, No. 3, 2005, pp. 261–264.Original Russian Text Copyright © 2005 by Veleshko, Kulyukhin.     

Synthesis and Structure of the Np(VII) Complex with Guanidinium,Li[C(NH<Subscript>2</Subscript>)<Subscript>3</Subscript>]<Subscript>2</Subscript>[NpO<Subscript>4</Subscript>(OH)<Subscript>2</Subscript>]·6H<Subscript>2</Subscript>O

The previously unknown Np(VII) compound Li[C(NH₂)₃]₂[NpO₄(OH)₂]·6H₂O (I), containing organic cations, was synthesized and studied by single crystal X-ray diffraction. In contrast to the relatively numerous structurally characterized salts of [NpO₄(OH)₂]^3– anions with Na⁺, K⁺, Rb⁺, and Cs⁺ cations, which were prepared only from strongly alkaline media, crystals of I were isolated from solutions with a very low concentration of OH^– ions (about 0.1 M). The compound is relatively stable in storage in the dry form, but is strongly hygroscopic. In the structure of I, there are two independent Np(VII) atoms with the oxygen surrounding in the form of tetragonal bipyramids. In contrast to the other salts of the [NpO₄(OH)₂]^3– anions with singlecharged alkali metal cations, the C(NH₂) ₃ ⁺ ions and hydrated Li⁺ ions in I interact with the oxygen surrounding of Np(VII) only via hydrogen bonds of types O_w–H···O and N–H···O with the formation of a three-dimensional H-bond network.