Chimie de l'uranium (VI) à l'interface solution/minéraux (quartz et hydroxyde d'aluminium) (expériences et caractérisations spectroscopiques)

This study deals with the understanding of the uranyl chemistry at the 0.1 M NaNO3 solution/mineral (quartz and aluminium hydroxide) interface. The aims are:(i) to identify and to characterize the different uranyl surface species (mononuclear, polynuclear complexes and/or precipitates...), i.e. the coordination environments of sorbed/precipitated uranyl ions, by using X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS) and time-resolved laser-induced fluorescence spectroscopy (TRLFS), and;(ii) to investigate the influence of pH, initial uranyl aqueous concentration and hydroxyl ligand concentration on the uranyl surface speciation.Our study on the speciation of uranyl ions at the quartz surface (i) confirms the formation of uranyl polynuclear/oligomers on quartz from moderate (1 mol/m2) to high (26 mol/m2) uranyl surface concentrations and (ii) show that theses polynuclear species coexist with uranyl mononuclear surface species over a pH range 5-8.5 and a wide range of initial uranyl concentration of the solutions (10-100 M). The uranyl concentration of these surface species depends on pH and on the initial uranyl aqueous concentration.Hydrate (surface-) precipitates and/or adsorbed polynuclear species and monomeric uranyl surface complexes are formed on aluminium hydroxide. Uranyl mononuclear complexes are predominant at acidic pH, as well as uranyl in solution or on the surface. Besides mononuclear species, precipitates and/or adsorbed polynuclear species are predominantly formed at neutral pH values on aluminium hydroxide. A main contribution of our investigations is that precipitation and/or adsorption of polynuclear species seem to occur at low uranyl surface concentrations (0.01-0.4 mol/m2). The uranyl surface speciation is mainly dependent on the pH and the aluminol ligand concentration.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF