Hydrothermal synthesis of (Zr,U)SiO: an efficient pathway to incorporate uranium into zircon.

The preparation of synthetic (Zr,U)SiO solid solution is challenging, as the conventional high-temperature solid-state method limits the solubility of uranium (4 ± 1 mol%) in the orthosilicate phase due to its thermodynamic instability. However, these compounds are of great interest as a result of (Zr,U)SiO solid solutions, with uranium contents exceeding this concentration, being observed as corium phases formed during nuclear accidents. It has been identified that hydrothermal synthesis pathways can be used for the formation of the metastable phase, such as USiO.

Chronicles of plutonium peroxides: spectroscopic characterization of a new peroxo compound of Pu(IV).

Although hydrogen peroxide (HO) has been highly used in nuclear chemistry for more than 75 years, the preparation and literature description of tetravalent actinide peroxides remain surprisingly scarce. A new insight is given in this topic through the synthesis and thorough structural characterization of a new peroxo compound of Pu(IV).

How hydrothermal synthesis improves the synthesis of (Zr,Ce)SiO solid solutions.

Although ZrSiO is the most well-known compound in the zircon-structured family (space group 4/), the experimental conditions for preparing pure and well-crystallized phases that are doped with a tetravalent element hydrothermal synthesis have never been clearly discussed in the literature. With the aim to answer this question, the experimental conditions of the preparation of ZrSiO and (Zr,Ce)SiO were investigated in order to synthesize well-crystallized and pure phases. A multiparametric study has been carried out using soft hydrothermal conditions with variables including reactant concentration, initial pH of the reactive medium, and duration of the hydrothermal treatment.

Correction: Formation of plutonium(IV) silicate species in very alkaline reactive media.

Correction for 'Formation of plutonium(IV) silicate species in very alkaline reactive media' by Paul Estevenon , , 2021, , 12528-12536, DOI: 10.1039/D1DT02248B.

Formation of plutonium(IV) silicate species in very alkaline reactive media.

Studying the speciation of Pu(IV) in very alkaline and silicate ion rich reactive media allowed identification of the formation of plutonium(IV)-silicate colloidal suspensions which were stable for months. These colloids were stabilized in aqueous solution for pH > 13 and for concentrations around 10 mol L. Successive filtration processes allowed evaluation of their size, which was found to be smaller than 6 nm.

The Role of Water and Hydroxyl Groups in the Structures of Stetindite and Coffinite, MSiO (M = Ce, U).

Orthosilicates adopt the zircon structure types (4), consisting of isolated SiO tetrahedra joined by A-site metal cations, such as Ce and U. They are of significant interest in the fields of geochemistry, mineralogy, nuclear waste form development, and material science. Stetindite (CeSiO) and coffinite (USiO) can be formed under hydrothermal conditions despite both being thermodynamically metastable.

Thermodynamics of CeSiO: Implications for Actinide Orthosilicates.

Zircon (ZrSiO, 4/) can accommodate actinides, such as thorium, uranium, and plutonium. The zircon structure has been determined for several of the end-member compositions of other actinides, such as plutonium and neptunium. However, the thermodynamic properties of these actinide zircon structure types are largely unknown due to the difficulties in synthesizing these materials and handling transuranium actinides.

study of the synthesis of thorite (ThSiO) under environmental representative conditions.

Thorite, (ThSiO4) with a zircon type structure, is one of the most abundant natural sources of thorium on Earth. Generally, actinides are known to form nanoparticles in silicate medium, though no direct link between those colloids and the crystalline form of thorite was evidenced until now. Here we show the formation of thorite from colloids and nanocrystalline structures under experimental conditions close to environmental pH and temperature.

The formation of PuSiO under hydrothermal conditions.

Attempts to synthesize plutonium(iv) silicate, PuSiO4, have been made on the basis of results recently reported in the literature for CeSiO4, ThSiO4, and USiO4 under hydrothermal conditions. Although it was not possible to prepare PuSiO4via applying the conditions reported for thorium and uranium, an efficient method of PuSiO4 synthesis was established by applying the conditions optimized for the CeSiO4 system. This method was based on the slow oxidation of plutonium(iii) silicate reactants under hydrothermal conditions at 150 °C in hydrochloric acid (pH = 3-4).

Formation of CeSiO from cerium(iii) silicate precursors.

Although the preparation of CeSiO4 has been already reported, the formation of pure cerium silicate from aqueous precursors appears as a challenge. An innovative way of synthesis has been identified in this study, allowing the formation of CeSiO4 after hydrothermal treatment starting from Ce(iii) silicate precursors. Among the experimental parameters examined, significant effects were found according to the nature of the precursor and of the reactive media considered, the pH of the reactive media and the temperature of the hydrothermal process.

Preparation of CeSiO from aqueous precursors under soft hydrothermal conditions.

Even though CeSiO was synthesized one time through a hydrothermal treatment, the conditions leading to its formation remain largely unknown. In order to define the optimized conditions of synthesis, a multiparametric study was developed by varying the pH of the solution, the temperature, and the nature of the reactants and of the complexing ions in solution. This study highlighted that CeSiO could not be obtained starting from Ce(iv) reactants.

Impact of Carbonate Ions on the Synthesis of ThSiO under Hydrothermal Conditions.

Multiparametric study of the hydrothermal synthesis of thorite, ThSiO, was performed with the aim to determine the most efficient conditions to form single phase thorite samples. Among the experimental parameters investigated, temperature of the hydrothermal process, concentration of carbonate ions, thorium and silicon reactants, and pH of the reactive media significantly affect the composition of the final system obtained. Single phase samples of ThSiO were prepared in weakly basic reactive media and at temperatures over 150 °C, for thorium and silicate concentrations higher than 8 × 10 mol L and carbonate concentrations of at least 8 × 10 mol L.

Multiparametric Study of the Synthesis of ThSiO under Hydrothermal Conditions.

A multiparametric study of the hydrothermal synthesis of ThSiO, thorite, was performed with the aim of determining the most efficient conditions to form single-phase samples. Among the experimental parameters examined, significant effects were found for the concentration of reactants in the starting mixture, pH of the reactive media, and temperature of the hydrothermal process. Such parameters affected both the rate of formation of thorite and the morphology of the final products synthesized.