Silvia Bulbulian

Synthesis of lithium silicates

Abstract Lithium silicates were synthesized by three techniques: (1) solid state reaction, (2) the precipitation method and finally, (3) the sol–gel method. Reactions were performed with different Li:Si molar ratios: 0.5, 1, 2 and 4. The obtained products were Li2SiO3, Li4SiO4 and Li2Si2O5. According to the synthesis method the composition of the samples changed as well as the morphology of the particles. The sol–gel method using CH3OLi provided the highest content of Li2SiO3 (94%); the solid state and precipitation methods provided pure Li4SiO4.

UO 2 2+ sorption on bentonite

The capacity of bentonite and purified bentonite to remove UO22+ ions from aqueous solutions has been investigated. The UO22+ uptake in these clays was determined for 0.2 and 0.002M uranyl nitrate solutions. It was found that under these conditions (0.2M) the maximum UO22+ uptake was 1.010±0.070 meq UO22+/g of bentonite and 0.787±0.020 meq UO22+/g of purified bentonite. In purified bentonite UO22+ sorption is irreversible up to 50 hours as no desorption was observed. Such is not the case in the natural bentonite. X-ray diffraction, thermal analyses, and transmission electron microscopy were used to characterize the solids. The uranium content was determined by neutron activation analysis.

Sorption of131I− by hydrotalcites

In this work, hydrotalcites were used to remove131I− from aqueous solutions. It was found that131I− sorption by hydrotalcites depends greatly on the thermal treatment of the solid and does not take place by ion exchange as I− is not capable of removing CO3−2 or other ions in the hydrotalcite. The anions have to be removed from the solid in order to permit I− to be sorbed in the hydrotalcite. The radionuclide content was determined by γ-spectrometry and X-ray diffraction was used to identify the compounds and to estimate cell parameters.

60Co sorption in zeolite 4A and effect of radiation

The potential uses of zeolites in the treatment of radioactive wastes may be conditioned to the physico-chemical properties of these materials. This work compares the Co sorption behavior of zeolite 4A and radiation treated zeolite 4A. Sorption experiments were performed with solutions containing labeled cobalt. No radiation effect (100 Mrad) in the zeolite structure or in the Co sorption behavior was found.

131I− Sorption by Thermally Treated Hydrotalcites

The sorption capacity of hydrotalcite (HT) and its calcined product (CHT) was evaluated for 131I− sorption from water solution and it was determined as a function of the calcining temperature. The radionuclide content was determined by γ-spectrometry. Solids were characterized by thermal analysis, X-ray diffraction (XRD), electron microscopy and Brunauer-Emmett-Teller (BET) analysis. For 0.1 M Na I solution, labeled with 131I−, sorption capacity was found to be 0.24 meq g−1 (7.2% of the anion exchange capacity, AEC). But, if the sample was previously calcined at 773 K and the HT structure destroyed, the sorption of I− increased considerably, up to 2.08 meq g−1 (63% of the AEC) and the HT structure was reconstructed. The 131I− sorption at very low concentrations (10−14M) was 0.04 × 10−14 meq of 131I− g−1 in the noncalcined HT, but for calcined samples at 773 K, the sorption increased to circa 0.97 × 10−14 meq g−1. Calcination temperature determines the surface area of the resulting mixed oxides, and that property seems to be the most important factor controlling the I− sorption. If the calcination temperature was increased to 873 K, the specific surface area of the oxide mixture increased and I− sorption increased as well, whereas calcination of HT at 973–1073 K resulted in a low surface area and a low I− retention.

131I− sorption from aqueous solutions by nitrated hydrotalcites

The sorption of radioactive iodide anion from aqueous solutions on hydrotalcite in the nitrate form has been investigated as a function of the Al/(Mg+Al) ratio. It was found that I− can replace only a small fraction of the nitrates in hydrotalcites and that I− sorption depends highly on Al/(Mg+Al) ratio.131I− was sorbed by anion exchange in the interlayer of hydrotalcite with an Al/(Mg+Al) ratio of 0.20 and, for higher ratios,131I− sorption increased more than 3 times. Hydrotalcites in the nitrate form were prepared using microwave irradiation in the hydrotreatment step. The radionuclide content was determined by Γ-spectrometry. Solids were characterized by BET, X-ray diffraction and atomic absorption analyses.

Phase transformations on lithium silicates under irradiation

Lithium silicates were synthesized by a precipitation method with a LirSi molar ratio of 4:1. The powders synthesized were mixtures of lithium silicates, Li SiO and Li SiO . Solids were characterized by X-ray diffraction. One of these 23 4 4 samples was prepared with an abnormal crystallization pattern. However, the crystallization pattern was corrected after irradiation either with neutrons or with gamma radiation. Furthermore, there was a phase transformation, Li SiO was the 44

Tritium recovery from nanostructured LiAlO2

Abstract In this work, a complex superlattice is obtained from a simple synthesis method. A detailed study by X-ray diffraction and electron microscopy is presented to determine the structural composition and the nanostructure of the obtained LiAlO 2 mixtures. To establish the influence of the superlattice presence in the tritium recovery, the obtained samples were irradiated with a mixed thermal and fast neutron flux in the nuclear reactor Triga Mark III (NRTMIII) at Salazar, Mexico. The study is focused on the superlattice effect on tritium mobility.

SOL–GEL SYNTHESIS OF LI2ZRSI6O15 POWDERS

Lithium silicozirconate (Li2ZrSi6O15) was synthesised by the sol–gel method. The synthesis was performed with several Li∶Zr∶Si molar ratios. The best yield of Li2ZrSi6O15 (89%) was obtained with the Li∶Zr∶Si molar ratio of 2∶2∶6. For molar ratios of Li∶Zr of 1 a mixture of oxides, such as SiO2 and ZrO2, was obtained. Moreover, when the Zr amount was higher than two, a mixture of oxides, lithium silicates and lithium zirconates was obtained.

EFFECTS OF γ RADIATION ON CHROMATE IMMOBILIZATION BY CALCINED HYDROTALCITES

The ability of hydrotalcites to retain anionic wastes was studied. In particular, Cr(VI)-adsorbed hydrotalcites were heated to immobilize Cr(VI) in the solid sample. When the heating temperature increased up to 500°C, the lamellar structure of hydrotalcite was lost. At high temperatures (1200°C), the solids were recrystallized in the form of a spinel. Lixiviation with 1 N and 5 N NaCl solutions were utilized to simulate the effect of sea water and of concentrated NaCl solutions in salt mines on the immobilization of Cr. Radiation damage on the solid containing the immobilized Cr was studied by γ-irradiating with a 60Co source at 1000 and 6000 kGy. The Cr-containing samples heated at 1200°C, whether irradiated or not, safely immobilized Cr in the hydrotalcite mainly in the form of MgCr2O4 spinel. Irradiation of hydrotalcites revealed two different effects: (1) samples heated up to 1200°C evolved as a solid in which chromium was retained more firmly than in the non-irradiated material, irradiation enhancing the spinel formation; (2) the structure of samples heated at 1200°C developed a preferential crystallite orientation rather than a purely random one or new location of chromium ions, this effect did not affect Cr immobilization in the solid. Chromium lixiviation with 5 N NaCl solution was always less than the corresponding value with 1 N NaCl solution, probably due to the poor mobility of Cl− ions in the highly concentrated NaCl solution.