X-ray absorption fine structure (XAFS) spectroscopy was employed to determine the bonding environment of As(V) in the presence of Cu(II) and Zn(II) on goethite and gibbsite. In addition, several mineral species and precipitates derived from homogeneous and heterogeneous (presence of alpha-Cr(2)O(3)) super-saturations were studied. Structural parameters were determined after resolving the broad ...

Hexavalent chromium (Cr(vi), present predominantly as CrO4(2-) in water at neutral pH) is a common ground water pollutant, and reductive immobilization is a frequent remediation alternative. The Cr(iii) that forms upon microbial or abiotic reduction often co-precipitates with naturally present or added iron (Fe), and the stability of the resulting Fe-Cr precipitate is a function of its mineral ...

Acid-base data for oxide minerals are fundamental building blocks for adsorption models. Although the influence of impurities is often discussed in a qualitative way, a quantitative analysis is largely missing. A notable exception is the discussion of the possible effect of surface impurities on the results of mass titrations. In the present contribution potential contaminations are discussed i...

U(VI) adsorption onto goethite-coated sand was studied in batch experiments ata solid-to-solution ratio (SSR) ranging from 33.3 to 333 g/L. Batch kinetic experiments revealed that the presence of 10(-4) M phosphate increased both the initial rate and ultimate extent of U(VI) adsorption compared with phosphate-free systems. Our experimental U(VI) adsorption isotherms were independent of SSR in p...

We study the influence of a magnetic field on the biaxial nematic phase of board-like goethite colloids both experimentally and theoretically. Using synchrotron small angle X-ray scattering techniques we find that applying a magnetic field along the main director of the biaxial nematic phase leads to a clear decrease in biaxiality with increasing magnetic field strength. Above a certain magneti...

Co(III) polyamine complexes with either two or three labile coordination sites bind strongly to high surface area metal oxides such as goethite or aluminium trihydroxide, and have been shown to act as passivating agents for aluminium flake in aqueous media, in addition to providing a potential method for surface functionalisation.

Experiments were performed herein to investigate the rates and products of heterogeneous reduction of Tc(VII) by Fe(II) adsorbed to hematite and goethite, and by Fe(II) associated with a dithionite–citrate–bicarbonate (DCB) reduced natural phyllosilicate mixture [structural, ion-exchangeable, and edge-complexed Fe(II)] containing vermiculite, illite, and muscovite. The heterogeneous reduction o...

Neutralisation of Acid Rock Drainage (ARD) by adding an alkaline reagent produces sludges generally dominated by amorphous ferrihydrite, often with high levels of adsorbed heavy metals. The effect of neutralisation method and reagent on the long-term chemical stability of these treatment sludges was investigated experimentally using a relatively oxidised synthetic ARD (containing Fe[~70% Fe], A...

This paper reports steady-state dissolution rates of synthetic low-substitution Al-goethites (mol % Al < 10) at pH 5 in the presence of the trihydroxamate siderophore, desferrioxamine B (DFO-B), and the common biological ligand, oxalate. The siderophore-promoted Fe release rate increased both with the level of Al substitution and with DFO-B concentration up to about 100 microM, after which a pl...

Heavy metal pollution presents a major hazard to the soil environment. Studies have shown that the activities of a variety of soil enzymes are inhibited by heavy metals. However, little information is available concerning the effect of heavy metals on the activity of enzymes immobilized by different soil constituents. The main objective of this work was to investigate the effects of copper on t...