Cerium In Solutions Research Articles

Cerium Ion Adsorption to Fluorine-Doped Tin Oxide Electrodes

The f-elements are critical in many technologies including electronics, catalysis, magnetics, and clean energy. Additionally, these elements occur in very low abundance worldwide. Research has therefore been motivated in the detection, quantification, and reclamation of these elements from waste streams. In this presentation we explore the use of fluorine-doped tin oxide (FTO) electrodes as sensitive and cost-effective electrochemical sensors for cerium ions. We demonstrate that cerium adsorbs reversibly to bare FTO surfaces with a dependence on pH. Through voltammetry and XPS characterization, we demonstrate that the adsorbed cerium, which can undergo the quasi-reversible CeIV/CeIII redox transition, exists in more than one chemical environment. Based on these data, we posit that these different environments are due to the buildup of multiple layers of cerium ions on the FTO surfaces. At lower concentrations (< ca. 100 uM), we can use voltammetry to quantify the cerium adsorbed to the FTO and relate it to the concentration of cerium in solution, with a lower detection limit of about 10-6 M. The data fits to a pseudo second order rate law with a rate constant on the order of 107 (cm2 mol-1)2 s-1. The adsorption fits well to the Freundlich model, but we are working towards finding a non-empirical adsorption model than provide the equilibrium constant for the adsorption reaction.

Hydrothermal conversion of mixed uranium(IV)-cerium(III) oxalates into U1-xCexO2+δ·nH2O solid solutions.

Uranium-cerium oxide solid solutions, U1-xCexO2+δ·nH2O, were prepared through hydrothermal conversion of mixed U(IV)-Ce(III) oxalate precursors, cerium being used as a surrogate for plutonium. Whatever the starting pH, the fluorite-type structure of AnO2 was obtained after heating at 250 °C for 24 h. The initial pH of the reaction media appeared to affect significantly the oxide morphology: for pH ≤ 2, the powder was found to be composed of microspheres, whereas for more alkaline pH values, agglomerates of nanocrystallites were found. Furthermore, a study of the hydrothermal treatment duration (T = 250 °C, pH = 8, t = 1-48 h) showed that fluorite-type mixed dioxides started to form after only 1 h, and then became single phase after 3 h. SEM and TEM/EDS analyses revealed that the cationic distribution narrowed with time to finally form highly homogeneous mixed oxides. Such a preparation route was then applied to various cerium incorporation rates and it was found that the formation of U1-xCexO2+δ·nH2O mixed oxides was possible for 0.1 ≤ x ≤ 0.75. In all the systems investigated, the speciation of uranium and cerium was questioned in both the solid and liquid phases. Thermodynamic calculations and evaluation of the O/M ratio in the final oxides led us to understand the complex redox behaviour of uranium and cerium in solution during hydrothermal processes and to propose a conversion mechanism.

Toxicity assay of lanthanum and cerium in solutions and soil

Lanthanum (La) and cerium (Ce) are one of the most abundant rare earth elements (REEs). In spite of quite extensive studying of the effects of these lanthanides on biota, some contradictions remain in the results. Also little is known about the effect of lanthanum and cerium on plant cells and their mitotic cycle, especially in soils. In this study, the effects of La and Ce in solutions and soil samples on root growth, mitotic index (MI) and frequency of aberrant cells (FAC) were assayed using one of the most convenient objects for testing of cytotoxicity – onion Allium cepa L. Bulbs were germinated on media containing La and Ce in concentrations 0–200 mg/l and 0–50 mg/l respectively for solutions and 0–200 mg/kg for soil samples. After 5 days of germination in solutions, a significant decrease in root elongation and MI in apical meristem cells are shown. We have also observed an increase in the number of cells with aberrations at 50 mg/l La and Ce concentration. The number of observed stickiness and disturbed metaphase has increased significantly. Soil samples turned out to be less toxic compared to the solutions probably due to the decreased availability of REEs. In spite of this, significant cytotoxicity of soil samples containing the highest concentration of La and Ce (200 mg/kg) is observed. The latter may indicate the importance of considering the cytotoxicity of soils containing high lanthanides concentrations – in extraction and production areas and actively fertilized fields.

The Effect of Borate on Cerium Film Formation

Cerium cations were found to inhibit corrosion of Aluminun alloys by the formation of a tetravalent cerium oxide film. The film forms by the oxidation of cerium in solution followed by precipitation under alkaline conditions. The process can be accelerated or facilitated by catalyzing the oxidation reaction, e.g., by the addition of hydrogen peroxide in solution. In this work a trivalent film was found to precipitate under similar conditions by the addition of borate to the solution. The addition of borate appears to stifle the oxidation of cerium in solution. The result is most likely the precipitation of an insoluble cerium compound followed by physical deposition.

The chemistry of solutions of CeO2 in cryolite melts

The solubility of CeO2 in cryolite has been investigated as a function of oxygen pressure, alumina content of the melt, and A1F3 content of the melt. Additional information comes from cryoscopic measurements, cyclic voltammetric studies, and thermodynamic calculations. The conclusions are that (a) cerium in solution is exclusively Ce(III), (b) the dominant species are CeOF and CeF3, the latter probably complexed as Na2CeF5, (c) control of oxygen pressure is of importance in measuring the solubility of the oxide of any metal that has more than one oxidation state, but (d) there may be serious kinetic difficulties in equilibrating gas and molten salt.

XIII. A redetermination of the atomic weight of cerium

XIII. A redetermination of the atomic weight of cerium