Inhibition of Uranium (VI) Sorption on Titanium Dioxide by Surface Iron (III) Species in Ferric Oxide/Titanium Dioxide Systems.

Uranium (U(VI)) sorption in systems containing titanium dioxide (TiO2) and various Fe(M)-oxide phases was investigated in the acidic pH range (pH 2.5-6). Studies were conducted with physical mixtures of TiO2 and ferrihydrite, TiO2 with coprecipitated ferrihydrite, and with systems where Fe(III) was mostly present as crystalline Fe(III) oxides. The presence of ferrihydrite resulted in decreased U(VI) sorption relative to the pure TiO2 systems, particularly below pH 4, an unexpected result given that the presence of another sorbent would be expected to increase U(VI) uptake. In mixtures of TiO2 and crystalline Fe(III) oxide phases, U(VI) sorption was higher than for the analogous mixtures of TiO2 with ferrihydrite, and was similar to U(VI) sorption on TiO2 alone. X-ray absorption spectroscopy of the TiO2 system with freshly precipitated Fe(III) oxides indicated the presence Fe(III) surface phase that inhibits U(VI) sorption-a reaction whereby Fe(III) precipitates as lepidocrocite and/or ferrihydrite effectively blocking surface sorption sites on the underlying TiO2. Competition between dissolved Fe(III) and U(VI) for sorption sites may also contribute to the observed decrease in U(VI) sorption. The present study demonstrates the complexity of sorption in mixed systems, where the oxide phases do not necessarily behave in an additive manner, and has implications for U(VI) mobility in natural and impacted environments where Fe(III) (oxyhydr)oxides are usually assumed to increase the retention of U(VI). © 2012, American Chemical Society

Uranium sorption in iron oxide/titanium oxide systems

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Removal of natural organic matter from source water: Review on coagulants, dual coagulation, alternative coagulants, and mechanisms

Natural organic matter (NOM) represents a range of soluble and insoluble material which can have considerable impact on drinking water quality. In addition to creating problems with taste, odour, clarification, and colour, removal of NOM is problematic because it can initiate the formation of disinfection by-products, which can adversely affect human health. Numerous technologies and methods have been employed to remove NOM in water treatment, with the most common processes involving the use of coagulants and similar technologies. This paper provides an overview of the most widely studied coagulants, coagulant aids, dual coagulants, and alternative coagulants. The paper also investigates the effects of operating parameters such as temperature, coagulant dose, pH, use of inorganic salts, inorganic polymeric coagulants, and organic polyelectrolytes in terms of charge neutralisation, polymer adsorption, and polymer bridging. Finally, emerging technologies and the use of novel coagulants are investigated

Optimisation of dual coagulation process for the removal of turbidity in source water using streaming potential

The charge at the surface of suspended particles and the degree of its neutralisation play an important role for achieving better turbidity removal efficiency in the coagulation process. Therefore, optimisation of the process critically requires continuous measurement or monitoring of surface charge. Streaming potential for this purpose can be considered as a good potential option in dual coagulation system. This study investigated factors that alter the streaming potential of source water, including pH, turbidity, humic acid concentration, inorganic coagulants, ionic strength, and polyelectrolyte concentrations. A range of dual coagulation systems were tested using the streaming potential to optimise coagulant doses., And jar test experiments were performed to estimate the extent of floc formation and turbidity reduction. Several inorganic and organic coagulants were combined in dual coagulation systems; Ferric chloride (FeCl3), Titanium chloride (TiCl4), and Aluminium chloride (AlCl3), Non-ionic polyacrylamide (PAM) and anionic polyacrylamide (aPAM). Turbidity removal efficiencies ranged from 83% to 99%. Ti (IV) systems gave the most efficient removal, which was not improved by the addition of polymer. PAM and aPAM added to Al (III) and Fe (III) flocculant systems, did improve the total removal efficiency and the rate of removal, with the effect more pronounced for Fe (III). Overall, PAM yielded the best results, particularly in combination with Fe (III). The streaming potential proved to be an excellent measure of optimum coagulant dosing