Removal of radioactive cesium, strontium, and iodine from natural waters using bentonite, zeolite, and activated carbon

Cs-134, Sr-85, and I-131 were produced by neutron irradiation of CsCl, SrCl₂, and K₂TeO₃, respectively, using the Kyoto University Reactor. These radioactive nuclides were added to river water and seawater to prepare artificially contaminated samples, and the removal of these nuclides using bentonite, zeolite, and activated carbon was then investigated. In the river water samples, Cs-134 and Sr-85 were successfully removed using bentonite and zeolite, and I-131 was removed using activated carbon. In the seawater samples, Cs-134 was removed using bentonite and zeolite, whereas Sr-85 and I-131 were hardly removed at all by these adsorbents.     

Removal of strontium from an aqueous solution using co-precipitation followed by microfiltration (CPMF)

This study characterized the removal of strontium from an aqueous solution via co-precipitation followed by microfiltration (CPMF) on a lab-scale. Sodium carbonate was used as the precipitating agent. Ferric chloride was added to a settler at a dosage of 20 mg/L to improve strontium removal, and it was added to a membrane separator at a dosage of 10 mg/L to reduce membrane fouling. The concentration of strontium in the raw water used in this study was about 5 mg/L. In two intermittent tests, where dosages of sodium carbonate were 2000 mg/L and 1000 mg/L, the mean decontamination factors (DFs) were 237 and 158 and the mean concentration factors (CFs) were 288 and 462, respectively. Although the mean DF value was lower when the sodium carbonate dosage was 1000 mg/L instead of 2000 mg/L, the rate at which the specific flux (SF) of the membrane declined decreased as the amount of the effluent treated increased. The problem of strontium release at the beginning of the operation was controlled by a continuous test in which the dosage of sodium carbonate still was 1000 mg/L and the other parameters were the same as in the other tests. The results showed that the mean DF and CF were 157 and 480, respectively.     

Removal of cesium radioisotopes from solutions using granulated zeolites

The influence of type of zeolite and the flow rate of solution through the column on the removal efficiency of radioactive cesium ions from solution has been investigated. The analysis of the change in the concentration of cesium ions in the solutions and distribution of cesium ions in the column fillings (granulated zeolites), after passing the solutions through the columns filled with various granulated zeolites (zeolite 4A, zeolite 13X, synthetic mordenite) was performed. On the basis of the results of this study, the conditions for the most efficient removal of cesium ions from solutions have been discussed.     

Adsorption of cesium on a composite inorganic exchanger zirconium phosphate - ammonium molybdophosphate

The applicability of zirconium phosphate-ammonium molybdophosphate (ZrP-AMP) for the efficient removal of cesium from aqueous acidic solutions by adsorption has been investigated. The adsorption data analysis was carried out using the Freundlich, Dubinin-Raduskevich (D-R) and Langmuir isotherms for the uptake of Cs in the initial concentration range of 3.75^.10^-5-7.52^.10^-3 mol^.dm^-3 on the ZrP-AMP exchanger from nitric acid medium. The mean free energy (E) values for the adsorption of Cs were obtained from the D-R isotherm. Equilibrium adsorption values at different temperatures have been utilized to evaluate the change in enthalpy, entropy and free energy (ΔH°, ΔS°, ΔG°). The adsorption of cesium on the ZrP-AMP exchanger was found to be endothermic. This revised version was published online in August 2006 with corrections to the Cover Date.     

Differential thermal analysis- studies on the crystallization of strontium tungstate from sodium tungstate melts

The kinetics of strontium tungstate crystallization from sodium tungstate melts in platinum crucibles were studied by differential thermal analysis at crystallization temperaturesT ₀=800, 900 and 1000° by continuous cooling at ratesR _T=40, 120 and 200° per hour. Heterogeneous nuclei that first formed on the metal platinate particles in the solution during the induction periods (t) grew to small crystallites (¯l). The main crystal growth started after the development of some excess solute concentration (Δ¯C) at the end of the induction temperatures (¯T). For the first 80% crystallization, the average crystal lengths (l _τ ) varied with the growth time (τ) according to the relation \(l_\tau ^2 = (\bar l)^2 + + 4\bar k_{D_1 } M\Delta \bar C\) where \(\bar k_{D1} \) is the diffusion rate constant at temperatures nearT, andM is the metal salt molecular weight. The initial growth rates and the ratiosl _τ ² /τ depended onΔ¯C instead ofR _T The last 20% growth was controlled only by the rate of development of the excess solute concentration.     

Removal of fluoride from aqueous solution using acid and thermally treated bone char

In this work, bone char (BC) was synthesized at different calcination temperatures and modified by using HNO₃ solutions having distinct concentrations. Furthermore, the relationship between the crystalline structure and physicochemical properties of BC on the adsorption capacity of BC towards fluoride from aqueous solution was analyzed. It was noted that the calcination temperature and the acid modification of BC significantly influenced the crystalline phases, crystallite size, and contents of hydroxyapatite, monetite, and other calcium phosphates, which are the main constituents of the BC. Additionally, the surface area diminished by raising both the calcination temperature and acid concentration used in the modification. The adsorption capacity of BC linearly declined as the calcination temperature was increased from 400 to 800 °C. On the other hand, BC modified with HNO₃ solutions showed that the adsorption capacity of BC was enhanced when monetite and hydroxyapatite with low crystallinity were present in these materials. Hence, the adsorption capacity of BC treated with acid was independent of textural properties. The adsorption capacity of BC was enhanced by increasing the solution pH due to the electrostatic interactions between the fluoride in the solution and the surface charge of BC. Finally, DRX, FTIR spectroscopy, and XPS studies corroborated that the fluoride adsorption mechanism on BC modified with acid solutions was influenced by electrostatic interactions and chemisorption between fluoride ions in solution and calcium phosphates from hydroxyapatite and monetite.     

Isotope exchange of strontium and molybdate ions in strontium polymolybdates

The heterogeneous isotopic exchange reactions in strontium polymolybdates of Sr²⁺ and MoO₄ ^2- ions in the strontium nitrate and sodium molybdate solutions have been studied using ⁹⁰Sr and ⁹⁹Mo as tracers. Electrometric methods have been used to study the compositions of strontium molybdates obtained by adding strontium chloride to a progressively acidified solution of sodium molybdate. It has been found that the exchange fraction increases with increasing chain length of strontium polymolybdate. The exchange equilibrium constant (K _ex) has been calculated between 298 and 348 K as well as DG°, DH° and DS°. The results indicate that Sr²⁺ cations have a much higher affinity for exchangers than MoO₄ ^2- anions. By fitting the data to the Dubinin-Radushkevich (D-R) isotherm it has been shown that the exchange capacity (X _m ) for both ions is affected by the ion adsorption process at low temperatures and by the ion exchange process at high temperatures. At high concentrations, the recrystallization process contributes to on the cation exchange but is ineffective on the anion exchange mechanism.     

Separation of strontium and yttrium in nitric acid solutions using zirconium titanium phosphate and Dowex exchangers

Sulfonated ion irradiated (H⁺ and He²⁺) PEEK films were synthesized with a range of cross-linking density and a variety of sulfonation degrees. Batch adsorption experiments were carried out at an initial pH of 6.0 ± 0.2, initial concentrations of Pb²⁺ and ¹³⁷Cs ions of 10.0 mg L⁻¹ and 5500 Bq L⁻¹, respectively. The maximum adsorption capacity was 60 mg g⁻¹ for Pb²⁺, and the distribution coefficient reached 6200 cm³ g⁻¹ for ¹³⁷Cs. The results indicated that sulfonation could be used to recycle low cross-linked PEEK and prepare efficient adsorbents to remove toxic Pb²⁺ and ¹³⁷Cs from polluted aqueous solutions.

     

Extraction behavior of moybdenum and zirconium with diisodecylphosphoric acid from nitric acid solution

This study was performed mainly from the viewpoint of consumption of diisodecylphosphoric acid (DIDPA) by the extracted Mo and Zr to estimate extraction capacities. The number of DIDPA molecules consumed per one extracted Mo atom was four when the concentration of Mo in the aqueous phase was less than 10^–3M and it decreased with increasing Mo concentration. Two molecules of DIDPA were consumed per one extracted Zr atom when the Zr concentration was high. Dependencies of the distribution ratio of Mo on the concentrations of Mo, DIDPA and HNO₃ are also described.     

Separation of actinides, cesium and strontium from marine samples using extraction chromatography and sorbents

Plutonium concentrations in seawater of the western North Pacific observed over the period from 1985 to 1997 are reported. In the 1990's, surface ^239,240Pu concentrations in the western North Pacific were relatively homogeneous (around 3 mBq/m³), although surface ^239,240Pu before the 1980's showed a latitudinal distribution with highs in mid-latitudes and lows in the Equatorial region. Temporal variations of surface ^239,240Pu in three different sea areas were examined. In mid-latitudes (21°–35°N), surface ^239,240Pu exponentially decreased with an apparent residence time of 9.9 years, whereas in the subtropical and Equatorial areas, decrease rates of surface ^239,240Pu were slower than in mid-latitudes. The vertical profiles of ^239,240Pu in mid-latitudes of the western North Pacific showed a surface minimum, a subsurface maximum and decreased with increasing depth. The water column inventory of ^239,240Pu at the station (27°48'N, 130°44'E) was calculated to be 113 Bq/m².     

Preparation and evaluation of composite ion-exchanger for the removal of cesium and strontium radioisotopes

Preparation conditions of composite ion-exchanger based on stannic molybdophosphate (SMP) and poly-acrylamide (PAA) have been described. Batch distribution coefficients for some ions were investigated at 25 °C. Sodium ion exchange capacity and breakthrough curves of cesium and strontium ions have also been determined. The results obtained from the experiments showed that the selectivity of SMP-PAA for cesium and strontium was greater than for other ions. Adsorption amounts of both ions were higher than 99% in demineralized water and their uptake rate were relatively rapid.     

Removal of iodate from aqueous solution using diatomite/nano titanium dioxide composite as adsorbent

Journal of Radioanalytical and Nuclear Chemistry - Highly deficient strontium cobaltite (SrCoOx), as a new nanomaterial that is thermally treated at low temperature...     

Structural studies of immobilized ethylenediamine as a preconcentrating agent for molybdate and tungstate

The structure of the complex formed between molybdate and the diamine functional group of N-β-aminoethyl-γ-aminopropylsilane (Dow Corning 2-6020) immobilized on a silica substrate is determined and compared with the analogous complex precipitated from solution. Infrared spectroscopy and photoacoustic spectroscopy were applied to establish the nature of the complex. The precipitate formed with ethylenediamine contains a polymeric molybdate species, whereas the molybdate retained by the immobilized ethylenediamine group is monomeric. Trace levels of tungstate and molybdate can be extracted from aqueous concentrated sodium chloride solutions on a column packed with controlled-pore glass beads treated with Z-6020.     

Uptake of cesium, strontium and europium by a poly(sodium acrylate-acrylic acid) hydrogel

The uptake of cesium, strontium and europium from dilute nitric acid solutions by a poly(sodium acrylate-acrylic acid) PAA hydrogel has been investigated. pH variations are consistent with cation exchange processes: COO(-), Na (+)H (+), COO(-), Na (+)M (m+) ( M (m+) = Cs (+)and Sr (2+)) and COOH Eu (3+). Saturation of the gel is achieved for metal/carboxylate ratios R = 0.5. The swelling ratios of gels loaded with metal cations are those of uncharged, shrunk gels (Sr, Eu) or of charged, swollen gels (Cs) in agreement with the formation of uncharged (COO)(2)Sr, (COO)(2)EuX (X = NO(3) or OH) type complexes and (COO(-), Cs(+)) ion pairs. The metal cations are extracted in the gels following the order of their affinities with carboxylic groups Eu(3+) > Sr(2+) > Cs(+). An increase of the ionic strength of the metal aqueous solution up to 0.5M NaNO(3) leads to slightly decrease the europium uptake by the PAA hydrogel, but 0.1M NaNO(3) is sufficient to prevent the Sr and Cs extractions.     

Uptake of cesium and strontium by crystalline silicotitanates from radioactive wastes

Crystalline silicotitanate inorganic ion exchanger, with a sitinakite structure is candidate material for remediation of aqueous nuclear waste streams. The syntheses of crystalline silicotitanate (CST) and Nb-substituted crystalline silcotitanate (Nb-CST) were carried out under hydrothermal conditions and the products were characterized using techniques viz., XRD, SEM/EDS, DTA/TGA, surface area respectively. Batch experiments were carried out to study the kinetics of uptake of ¹³⁷Cs and ⁹⁰Sr, to estimate the decontamination factor (DF) values and distribution coefficients (K _d) for the above synthesized CST and Nb-CST samples from actual radioactive waste solutions. The DF values for uptake of Cs and Sr by Nb-CST after 24 h of equilibration was 355 and 136 whereas for CST it was found to be 40 and 176 respectively. The K _d values for uptake of Cs and Sr for Nb-CST after 24 h of equilibration was found to be 35,490 and 13,500 mL/g respectively whereas the K _d values for uptake of Cs and Sr for CST was found to be 4,025 and 17,525 mL/g respectively. The ion exchange capacity of Nb-CST towards ⁹⁰Sr and ¹³⁷Cs was estimated to be 11.8 and 3.2 meq/g respectively whereas the ion exchange capacity of CST towards ⁹⁰Sr and ¹³⁷Cs was estimated to be 14.6 and 4.4 meq/g respectively.     

On the separation of cesium and strontium from oxalate filtrate by neutralization

At the treatment of HLLW (high-level liquid radioactive waste) by oxalate precipitation, the filtrate is occured as a waste. But various elements including Cs and Sr are contained in the oxalate filtrate. It is very important, therefore, to separate from each other in a viewpoint of ultimate isolation of heat generating nuclides such as Cs and Sr from HLLW. In this study, the simulated oxalate filtrate, consisted of five elements (Cs, Sr, Ru, Fe and Mo) and organics (oxalic acid and ascorbic acid), was prepared, from which the separation of Cs and Sr was carried out by neutralization with NaOH. As a result, the simulated solution could be divided into Cs, Sr and Ru containing groups with pH. Sr was readily precipitated as forms of Sr(C₂O₄)·nH₂O at pH 3. Iron and ruthenium were also co-precipitated around pH 8, and Cs and Mo remained in the resulting solution.     

Adsorption of cesium and strontium on natrified bentonites

The influence of chemical activation–natrification of bentonites on adsorption of Cs and Sr was studied with regards to utilization of bentonites for depositing high-level radioactive waste and spent nuclear fuel. Bentonite samples from three Slovak deposits in three different grain-size (15, 45 and 250 μm), natural and natrified forms (Na-bentonites); under various experimental conditions, such as contact time, adsorbent and adsorbate concentration have been studied. When comparing the Na-bentonites and their natural analogues, the highest adsorbed Cs and Sr amounts were reached on the natrified samples. After the Sr adsorption a drop in the pH equilibrium value was observed together with the increase of the initial Sr concentration. A disadvantage of the natrified bentonite forms is formation of colloid particles. After 2 h of phase mixing a gentle turbidity was observed as well as formation of a gel-like form. The above findings were confirmed by observing the particle distribution in dry and wet dispersion and centrifugation at two different speeds. Natrification as a technological process of bentonite quality improvement cannot be applied when constructing a long-term repository for high-level radioactive waste and spent nuclear fuel. The main problem of natrification is a technological process which leads to a significant pH increase. Alkaline environment in combination with the K presence and increased temperature in the vicinity of radio-active waste can lead to a rapid illitization of smectite and loss of the original adsorption qualities. Moreover, sodium additions are a significant point of uncertainty since it is not possible to state what amount of Na enters the interlayer space and what amount stays in the inter-partition space.     

Differential thermal analysis studies on the crystallization of strontium tungstate from sodium tungstate melt. Nucleation mechanism and induction periods

The nucleation mechanism, kinetics and induction periods in strontium tungstate crystallization from sodium tungstate melt in platinum crucibles were investigated by differential thermal analysis. Heterogeneous nuclei first formed on the metal platinate particles within the solution during the induction periods (¯t); the main crystal growth started only after ¯t and few new nuclei were then formed. At any crystallization temperature, ¯t varied inversely with the cooling rate (R _T), and with the rate (R_C) of development of excess solute concentration according to the relation ¯t = 1/(k ₁ R _c ), wherek ₁ and are constants. The critical temperature (¯T), critical supersaturation(¯ S), k ₁ and were evaluated.

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Zusammenfassung Der Keimbildungsmechanismus, sowie die Kinetik und die Induktionsperioden wurden bei der Kristallisation von Strontiumwolframat aus Natriumwolframatschmelzen in Platintiegeln durch Differentialthermoanalyse untersucht. Die heterogenen Kristallkeime wurden zuerst während der Induktionsperiode () an den Metallplatinat-Teilchen in der Lösung gebildet: das Hauptkristallwachstum begann erst nach und nachfolgend wurden einige neue Keime gebildet. Bei jeder Kristallisationstemperatur änderte sich umgekehrt proportional zu den Abkühlungsgeschwindigkeiten (R _T) und den Geschwindigkeiten (R _c) der Bildung überschüssig gelösten Materials, entsprechend der Gleichung = 1/(k ₁ R _c , wobeik ₁ und Konstanten sind. Die kritische Temperatur (¯T), die kritische Übersättigung (¯S),k ₁ und wurden bewertet.

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Résumé On a étudié par analyse thermique différentielle le mécanisme de nucléation ainsi que la cinétique et les périodes d'induction de la cristallisation du tungstate de strontium, à partir des bains fondus de tungstate de sodium, dans des creusets de platine. Des noyaux hétérogènes se forment d'abord sur les particules de platinate métallique dans la solution, au cours des périodes d'induction (): la croissance principale des cristaux ne commence qu'après et il se forme alors quelques noyaux nouveaux. A une température quelconque de cristallisation, varie de façon inverse avec les vitesses de refroidissement (R _T) et les vitesses de développement (R _c ) de concentrations de sursaturation de la substance en solution, selon la relation = 1/(k ₁ R _c , oùk ₁ et sont des constantes. On a évalué la température critique (¯T), la sursaturation critiques (¯S),k ₁ et.

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, . - (¯ t). ¯t . - ,¯t (R _T), (R _c) ¯t=1/(K₁ R _c ), ₁ — . (¯), (_-S), K₁ .