Fluoride determination in various matrices relevant to nuclear industry: A review

MASS SPECTROMETRY-BASED TECHNIQUES FOR DIRECT QUANTIFICATION OF HIGH IONIZATION ENERGY ELEMENTS IN SOLID MATERIALS-CHALLENGES AND PERSPECTIVES

The determination of nonmetals, first of all, the most electronegative ones-nitrogen, oxygen, fluorine, chlorine, and bromine, poses the highest challenge for element analysis. These elements are characterized by high reactivity, volatility, high ionization energy, and the absence of intensive spectral lines in the optical spectral range. Conventional techniques of their quantification include considerable "wet chemistry" stages so the application of these techniques for the solid sample is highly laborious and prone to uncontrollable uncertainties. Additionally, current development in material science and other areas requires the quantification of the elements at lower levels with good sensitivity. Owing to their robustness and flexibility, mass spectrometry techniques provide vast possibilities for the quantification, spatial and isotopic analysis, including the solutions for direct analysis of solids. The current review focuses on the application of major mass spectrometric techniques for the quantification of N, O, F, Cl, and Br in solid samples. The following techniques are mainly considered: thermal ionization mass spectrometry (TIMS), isotope-ratio MS (IRMS), secondary ion MS (SIMS), inductively coupled plasma MS (ICP-MS), and glow discharge MS (GDMS); as the most accessible and widely applied for the purpose. General ionization issues, advantages, limitations, and novel methodological solutions are discussed. © 2020 John Wiley & Sons Ltd.

A study of matrix and admixture elements in fluorine-rich ionic conductors by pulsed glow discharge mass spectrometry

RATIONALE

Dopants in ionic conductors play a crucial role in achieving the required electrochemical properties. A slight variation in their concentration considerably affects the conductivity of crystals and their applicability as ionic conductors and laser materials. To ensure the growth of high-quality fluoride crystals, adequate approaches for the quantification of matrix and admixture/dopant components are required.

METHODS

A panel of SrF₂ - and GdF₃ -doped LaF₃ single crystals was investigated. The electrical conductivity of the crystals was measured using impedance spectroscopy in the frequency range 100 Hz-1 MHz to control for crystal quality. Pulsed glow discharge mass spectrometry (GDMS) was used to simultaneously quantify fluorine, strontium, lanthanum, and gadolinium in the crystals. X-ray fluorescence, scanning electron microscopy-energy dispersive X-ray spectroscopy, and arc optical emission spectrometry were used for validation.

RESULTS

Quasiperiodic intensity drifts under sputtering of the ionic conductors were observed and attributed to F^- redistribution on the sample surface, affecting surface conductivity and sputtering rate. Several sample preparation protocols were tested to address that effect. Full coating of the sample with a layer of silver several micrometers thick provided stable and effective sputtering. The parameters for the GDMS determination of F, Sr, La, and Gd were optimized. The elements' distribution was studied in different parts of the crystals.

CONCLUSIONS

An analytical approach to the direct multi-element analysis of fluoride-containing ionic conductors using pulsed GDMS with La_1-x-y Sr_x Gd_y F_3-x as an example was designed and tested. Instability effects of ionic conductivity were explained and coped with, providing effective and stable sputtering.

Preparation of a novel CeO2/SiO2 adsorbent and its adsorption behavior for fluoride ion

The silica-based CeO2 adsorbent (CeO2/SiO2) was prepared for removing fluoride from the aqueous solution. The synthesized adsorbent was characterized by scanning electron microscope, energy dispersive spectrum, X-ray diffractometer, Fourier transform infrared spectrometer, and zeta potential measurement analyses. The adsorption batch experiments in the various experimental conditions including solution pH, contact time, initial fluoride concentration, and adsorption temperature were performed and investigated. The maximum adsorption capacity of fluoride into CeO2/SiO2 was 2.441 mmol/g at pH 3 and 298 K. The adsorption kinetics and isotherms were well described by the pseudo-second-order model and the Langmuir model, respectively. The fluoride adsorption reached the equilibrium in 15 min from the aqueous solution with the initial fluoride concentration of 400 mg/l at 298 K. In the temperature range of 298–338 K, the maximum adsorption capacity of fluoride decreased from 2.441 mmol/g to 2.109 mmol/l at pH 3. The adsorption thermodynamics study revealed that this process was a spontaneous, exothermic, and entropy-driving adsorption. Furthermore, the mechanism of adsorption was identified as the anion exchange and the electrostatic interaction. The desorption efficiency of fluoride-loaded CeO2/SiO2 adsorbent could reach about 95% by 0.1 mol/l NaOH.

Direct Separation of Molybdenum from Solid Uranium Matrices Employing Pyrohydrolysis, a Green Separation Method, and Its Determination by Ion Chromatography

Pyrohydrolysis is a well-established separation method, and it is being used as a sample preparation method for several materials for further determination of non-metals such as halogens, boron, and sulfur. Analytes are retained in a diluted solution that is suitable for carrying out analysis by several determination techniques and minimizing the use of concentrated reagents. Pyrohydrolysis separation of metals has not been reported yet. The present study demonstrates the pyrohydrolysis separation of Mo as MoO4(2-) from uranium materials and its subsequent determination using ion chromatography coupled with suppressed conductivity detector. With use of TGA and XRD the volatilization behavior of Mo was studied. Important parameters for the pyrohydrolysis method required for the quantitative separation of Mo were evaluated. The precision of the method was better than 5% at 25 ppm of Mo. The accuracy was evaluated by analysis of a CRM (U3O8-ILCE-IV). The method was applied to determine Mo in ammonium diuranate samples, where the conventional methods suffer from the loss of Mo.

Analysis methods for meso- and macroporous silicon etching baths

: Analysis methods for electrochemical etching baths consisting of various concentrations of hydrofluoric acid (HF) and an additional organic surface wetting agent are presented. These electrolytes are used for the formation of meso- and macroporous silicon. Monitoring the etching bath composition requires at least one method each for the determination of the HF concentration and the organic content of the bath. However, it is a precondition that the analysis equipment withstands the aggressive HF. Titration and a fluoride ion-selective electrode are used for the determination of the HF and a cuvette test method for the analysis of the organic content, respectively. The most suitable analysis method is identified depending on the components in the electrolyte with the focus on capability of resistance against the aggressive HF.