Sequential determination of uranium (IV), free acidity and hydrazine in a single aliquot

Design of experiments for the optimization of U(VI) reduction with hydrogen over Pt/SiO2

Significant amount of uranous nitrate is required for reducing Pu(IV) into inextractable Pu(III) for partitioning of U(VI) and Pu(IV) present in the loaded organic phase in PUREX process. Experiments have been conducted for the preparation of uranous nitrate by reducing uranyl nitrate present in nitric acid solution using hydrogen over Pt/SiO2 catalyst. The effect of process variables such as U(VI) concentration, H2 pressure, nitric acid concentration, catalyst quantity, temperature, mixing speed, and hydrazine concentration (for stabilizing U(IV)) on the yield of U(IV) was studied. The process variables were optimized by a two-step statistical approach namely design of experiments. The initial screening of process variables and determination of important variables that affect the production of U(IV) was determined by definitive screening design (DSD) methodology. The DSD yielded three variables affecting the U(VI) reduction to a significant extent were U(VI) concentration, H2 pressure and mixing speed. These significant variables were further optimized using five-level full factorial central composite design (CCD) methodology for understanding the intricate interactions between the variables and the combined effect of all variables at a time influencing the U(VI) reduction. A second-order polynomial equation derived from CCD was subjected to analysis of variance (ANOVA) for estimating the validity of the model and statistical significance of the terms involved in the polynomial. The results revealed that the model can predict the yield of U(IV) generation with 95% confidence in the proposed experimental range.

Microfluidic In-Situ Spectrophotometric Approaches to Tackle Actinides Analysis in Multiple Oxidation States

The study and development of present and future processes for the treatment/recycling of spent nuclear fuels require many steps, from design in the laboratory to setting up on an industrial scale. In all of these steps, analysis and instrumentation are key points. For scientific reasons (small-scale studies, control of phenomena, etc.) but also with regard to minimizing costs, risks, and waste, such developments are increasingly carried out on milli- or microfluidic devices. The logic is the same for the chemical analyses associated with their follow-up and interpretation. Due to this, over the last few years, opto-microfluidic analysis devices adapted to the monitoring of different processes (dissolution, liquid-liquid extraction, precipitation, etc.) have been increasingly designed and developed. In this work, we prove that photonic lab-on-a-chip (PhLoC) technology is fully suitable for all actinides concentration monitoring along the plutonium uranium refining extraction (plutonium, uranium, reduction, extraction, or Purex) process. Several PhLoC microfluidic platforms were specifically designed and used in different nuclear research and development (R&D) laboratories, to tackle actinides analysis in multiple oxidation states even in mixtures. The detection limits reached (tens of µmol·L^-1) are fully compliant with on-line process monitoring, whereas a range of analyzable concentrations of three orders of magnitude can be covered with less than 150 µL of analyte. Finally, this work confirms the possibility and the potential of coupling Raman and ultraviolet-visible (UV-Vis) spectroscopies at the microfluidic scale, opening the perspective of measuring very complex mixtures.

Spectroscopic study on the reactions of bis-salophen with uranyl and then with fructose 1,6-bisphosphate and the analytical application

The chelating reaction of bis-salophen with uranyl to form binuclear complex uranyl-bis-salophen (UBS) was studied by fluorescence spectroscopy. The coordination reaction of UBS with fructose 1,6-bisphosphate (F-1,6-BP) to form supramolecular polymer was then studied by resonance light scattering (RLS) spectroscopy. The reaction of bis-salophen with uranyl results in a remarkable enhancement of fluorescence intensity. The maximum emission wavelength of the fluorescence is at 471nm. The reaction of UBS with F-1,6-BP results in a remarkable enhancement of RLS intensity. The maximum scattering wavelength of the RLS is at 460nm. The two reactions were used to establish fluorescence method for the determination of uranium (VI) and RLS method for the determination of F-1,6-BP, respectively. Under optimum conditions, the linear ranges for the detection of uranium (VI) and F-1,6-BP are 0.003-0.35nmol/mL and 0.05-5.0nmol/mL, respectively. The detection limits are 0.0017nmol/mL and 0.020nmol/mL, respectively. The proposed fluorescence method has been successfully applied for the determination of uranium (VI) in environmental water samples with the recoveries of 97.0-104.0%. The proposed RLS method has also been successfully applied for the determination of F-1,6-BP in medicine injection samples with the recoveries of 98.5-102.3%.

Separation and determination of trace uranium using a double-receptor sandwich supramolecule method based on immobilized salophen and fluorescence labeled oligonucleotide

A double-receptor sandwich supramolecule method for the separation and determination of trace uranium was proposed in this paper. One receptor is a salophen which can react with uranyl to form a uranyl-salophen complex, and another receptor is an oligonucleotide which can bind uranyl to form oligonucleotide-uranyl-salophen supramolecule. The salophen was immobilized on the surface of silica gel particles and used as the solid phase receptor for separating uranium from solution. The oligonucleotide was labeled with a fluorescent group and used as the labeled receptor for quantitatively analyzing uranium. In the procedure of separation and determination, uranyl ion was first combined with the solid phase receptor and then conjugated with the labeled receptor to form the sandwich-type supramolecule. The labeled receptor in the sandwich supramolecule was then eluted and determined by fluorescence analysis. The experimental results demonstrate that this method has a number of advantages such as high selectivity, excellent pre-concentration capability, high sensitivity, good stability and low cost. Under optimal conditions, the linear range for the detection of uranium is 0.5-30.0 ng mL(-1) with a detection limit of 0.2 ng mL(-1). The proposed method was successfully applied for the separation and determination of uranium in real samples with the recoveries of 95.0-105.5%.