Karin Popa

The sorption of some radiocations on microporous titanosilicate ETS-10

The microporous titanosilicate ETS-10 synthesized from gel with following molar composition: 1.0 Na2O: 1.49 SiO2 : 0.2 TiO2 : 0.6 KF : 1.28 HCl : 39.5 H2O was subjected to sorption of radioactive cations 115Cd2+, 204Hg2+, 60Co2+ and 137Cs+ (M) from aqueous solution, in the absence of ionic competition. The uptake of these cations on the ETS-10 was compared by means of the distribution coefficient (Kd) versus contact time and sorption capacity (R) at equilibrium. The FT-IR spectra of M-ETS-10 sorption products exhibit a modification of the absorption band, principally at 381 cm-1.

Use of some oxides in radiolytical decomposition of water

Abstract This paper deals with a study on the radiolysis of water in the presence of certain oxides: BeO, SiO2, TiO2, ZrO2 acting as catalysts for the hydrogen production. A radionuclide of 60Co with an activity of about 5×104 Ci was employed as an irradiation γ source. A considerable increase (up to ten times or more) of the amount of hydrogen resulting from the radiolysis of water in the presence of the above mentioned oxides was noticed in comparison with a reference sample, irradiated under the same experimental conditions, but without any catalyst. The radiolysis products have been identified by means of a method based on mass spectrometry.

Triclinic–Cubic Phase Transition and Negative Expansion in the Actinide IV (Th, U, Np, Pu) Diphosphates

The AnP(2)O(7) diphosphates (An = Th, U, Np, Pu) have been synthesized by various routes depending on the stability of the An(IV) cation and its suitability for the unusual octahedral environment. Synchrotron and X-ray diffraction, thermal analysis, Raman spectroscopy, and (31)P nuclear magnetic resonance reveal them as a new family of diphosphates which probably includes the recently studied CeP(2)O(7). Although they adopt at high temperature the same cubic archetypal cell as the other known MP(2)O(7) diphosphates, they differ by a very faint triclinic distortion at room temperature that results from an ordering of the P(2)O(7) units, as shown using high-resolution synchrotron diffraction for UP(2)O(7). The uncommon triclinic-cubic phase transition is first order, and its temperature is very sensitive to the ionic radius of An(IV). The conflicting effects which control the thermal variations of the P-O-P angle are responsible for a strong expansion of the cell followed by a contraction at higher temperature. This inversion of expansion occurs at a temperature significantly higher than the phase transition, at variance with the parent compounds with smaller M(IV) cations in which the two phenomena coincide. As shown by various approaches, the P-O(b)-P linkage remains bent in the cubic form.

Thermodynamic properties of CaTh(PO4)2 synthetic cheralite

Abstract The mineral cheralite [CaTh(PO4)2] allows for the incorporation of tetravalent actinides in monazitebased crystalline phases. Experimental determination of its thermodynamic properties is crucial for defining its stability and subsequent long-term ability to immobilize radionuclides. Low-temperature heat capacity from 0.5 to 300 K, enthalpy increments from 485 to 1565 K, and the enthalpy of formation of cheralite from the oxides were measured and reported on for the first time. At 298.15 K, S° = (201.6 ± 2.6) J/(K·mol), which includes the configurational entropy of Ca and Th mixing, ΔHfox = -(506.4 ± 9.5) kJ/mol, ΔHfel = -(3872.8 ± 10.2) kJ/mol, ΔGfox = -(501.6 ± 9.6) kJ/mol, and ΔGfel = -(3635.5 ± 10.2) kJ/mol. In aqueous environments, cheralite is able to form from whitlockite or apatite and thorianite. Under anhydrous conditions, cheralite can form by solid-state reaction only if the resultant product includes very stable Ca salts instead of CaO.

Contrasting immobilization behavior of Cs+ and Sr2+ cations in a titanosilicate matrix

ETS-10 titanosilicate was tested as an adsorbent for the removal of Cs+ and Sr2+ cations from radioactive waters, considering both the ion exchange and the behaviour of the loaded adsorbent during thermal conditioning. The studies indicate that ETS-10 has a high and similar affinity for both Cs+ and Sr2+ cations reaching the ion exchange capacity of ETS-10 at a concentration of about 50 milliequivalents gram per liter. Thermal treatment of Cs+- and Sr2+-exchanged ETS-10 materials results in melting at approximately 700 °C. The melting temperature increases with the initial Cs+ and Sr2+ concentration and is higher for Sr2+ than for Cs+ exchanged ETS-10. Recrystallisation occurs only in the presence of Sr2+ as evidenced by the exothermic effects between 800 and 900 °C. After calcination of Cs+- and Sr2+-exchanged ETS-10 in air at 800 °C, two types of materials were obtained: an amorphous glass material with homogeneous Cs+ distribution and a strontium fresnoites glass–ceramic material.

Decontamination of radioactive liquid wastes by hydrophytic vegetal organisms

This paper deals with the bioaccumulation of some radioactive ions from contaminated waste solutions, on hydrophytic vegetal organisms. In order to follow the distribution of radioactive ions 137Cs+, 60Co2+ and 51Cr3+ in various cell components extracted from Spirulina platensis, Porphiridium cruentum, Scenedesmus quadricauda, Lemna minor,Elodea canadensis, Pistia stratiotes and Riccia fluitans, the plants were cultivated in radioactive solutions. The resulting complexes were extracted with acetone or acetic acid and separated chromatographically. The results show an intense activity of the polysaccharide and lipoid fractions in the bioaccumulation process. The bioaccumulation varies in the series: Spirulina>Scenedesmus>Porphiridium>Riccia>Pistia> Lemna3Elodea for 137Cs+ and 60Co2+; Spirulina>Porphiridium>Scenedesmus>Riccia>Pistia>Lemna>Elodea for 51Cr3+.

Improvement of retention capacity of ETS-10 for uranyl ions by porosity modification and their immobilization into a titanosilicate matrix

The retention capacity of ETS-10 titanosilicate for uranyl ions was improved by generation of additional intra-crystalline porosity with formation of an extended silica-rich surface area. Chemical bonds between uranyl groups and [SiO4] tetrahedra were found. By calcination at 800 °C, the uranium-loaded ETS-10 transforms into a inert titanosilicate matrix that encapsulates uranium.

Effect of radioactive and non-radioactive mercury on wheat germination and the anti-toxic role of glutathione

Studies to test the noxious effect of mercury ions on wheat germination and seedling growth showed that germination rate, shoot length, and fresh weights varied as a function of their concentration in the treatment solutions. At the same concentration, the radioactive mercury proved to be more harmful to the living seeds and seedlings. The detoxification action of glutathione for both radioactive and non-radioactive mercury was also followed. After a seven-day period of germination in the presence of the investigated compounds, the wheat plantlets were cut from the seeds, and their height, weight, and residual radioactivity were measured. The shoot length decreased from 8.1 (blank) to 4.6 cm (non-radioactive mercury) or even to 2.5 cm (203Hg), while glutathione had both an anti-toxic and an anti-radiotoxic effect (6.4 and 6.0 cm, respectively). The root weight of the lot decreased from 1.7 to 0.7 g and 0.4 g, respectively, while glutathione showed a healing action (1.5 and 1.7 g). The radioactive ions accumulated especially in roots (35.5 %), and less in shoots (11.2 %). Results were statistically validated.

Laboratory analyses of 60Co2+, 65Zn2+ and 55+59Fe3+ radiocations uptake by Lemna minor

The living Lemna minor vascular plant and two different sorbents obtained by chemical treatment of this plant were tested to study the removal process of 60Co2+, 65Zn2+ and 55+59Fe3+ from low radioactive wastewaters. The most effective sorbent was the protonated biomass, indicating the decisive contribution of the complexation process in the assembly of the uptake mechanisms. The uptake performance of the biosorbent obtained from the L. minor can be increased with ∼20% by treatment with 0.1 N HNO3. Concerning the metabolically active mechanism, it can be notice the slow elimination of 65Zn2+ and the continuously increase of 55+59Fe3+ uptake degree. The Na2CO3 generated in situ in systems participates to a double exchange reaction with the metallic cations during the uptake. 60Co2+, 65Zn2+ and 55+59Fe3+ radiocations prefer for coordination N-donor ligands at the expense O-donors ones.

Determination of REE, U, Th, Ba, and Zr in simulated hydrogeological leachates by ICP-AES after matrix solvent extraction

Abstract A fast, reliable and precise method for the determination of Ba, Zr, Th, U, La, Ce, Eu, Hf and Gd in leaching solutions containing up to 1 mol/L FeCl3 by inductively coupled plasma-atomic emission spectrometry (ICP-AES) was described. Liquid-liquid extraction with diethyl ether was applied for selective and quantitative extraction of the iron with a decontamination factor of 65000. The study has enabled the determination of rare earth elements, U, Th Ba, and Zr, from the solution with high iron content with detection limits in the range of 1–24 ng/ml and a precision of 0.9%–4.6 % relative standard deviation. The developed method was simple and was adopted for implementation in a glove box for handling radioactive materials.