Georges Ona-Nguema

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The modes of As(III) sorption onto two-line ferrihydrite (Fh), hematite (Hm), goethite (Gt), and lepidocrocite (Lp) have been investigated under anoxic condition using X-ray absorption spectroscopy (XAS). X-ray absorption near-edge structure spectroscopy (XANES) indicates that the absence of oxygen minimized As(III) oxidation due to Fenton reactions.(More)
Green rust (GR) as highly reactive iron mineral potentially plays a key role for the fate of (in)organic contaminants, such as chromium or arsenic, and nitroaromatic compounds functioning both as sorbent and reductant. GR forms as corrosion product of steel but is also naturally present in hydromorphic soils and sediments forming as metastable intermediate(More)
Euglena gracilis is a photosynthetic eukaryote ubiquitous in arsenic-polluted acid mine drainages and is locally exposed to As(III) and As(V) concentrations up to 250 and 100 mg L(-1), respectively. Here, arsenic speciation in E. graciliswas determined by X-ray absorption spectroscopy and selected (bio)chemical methods on cells grown at nonlimiting(More)
Arsenic sorption onto maghemite potentially contributes to arsenic retention in magnetite-based arsenic removal processes because maghemite is the most common oxidation product of magnetite and may form a coating on magnetite surfaces. Such a sorption reaction could also favor arsenic immobilization at redox boundaries in groundwaters. The nature of arsenic(More)
To reduce the adverse effects of arsenic on humans, various technologies are used to remove arsenic from groundwater, most relying on As adsorption on Fe-(oxyhydr)oxides and concomitant oxidation of As(III) by dissolved O(2). This reaction can be catalyzed by microbial activity or by strongly oxidizing radical species known to form upon oxidation of Fe(II)(More)
Bioreduction of the well-crystallized ferric oxyhydroxide gamma-FeOOH lepidocrocite was investigated in batch cultures using Shewanella putrefaciens bacterium (strain CIP 8040) at initial pH 7.5 in bicarbonate buffer. The cultures were performed with formate as electron donor without phosphate, in the presence or absence of anthraquinone-2,6-disulfonate(More)
Arsenic sorption onto iron oxide spinels such as magnetite may contribute to arsenic immobilization at redox fronts in soils, sediments, and aquifers, as well as in putative remediation and water treatment technologies. We have investigated As(V) speciation resulting from different sorption processes on magnetite nanoparticles, including both adsorption and(More)
Arsenic sorption onto iron oxide spinels such as magnetite could contribute to immobilization of arsenite (AsO3(3-)), the reduced, highly toxic form of arsenic in contaminated anoxic groundwaters, as well as to putative remediation processes. Nanocrystalline magnetite (<20 nm) is known to exhibit higher efficiency for arsenite sorption than larger(More)
Bacterial activity is commonly thought to be directly responsible for denitrification in soils and groundwater. However, nitrate reduction in low organic sediments occurs abiotically by FeII ions within the fougerite mineral (IMA 2003-057), giving the bluish-green color of gleysols. Fougerite, the mineral counterpart of FeII-III oxyhydroxycarbonate,(More)
Ferrihydrite (Fh) is a nanocrystalline ferric oxyhydroxide involved in the retention of pollutants in natural systems and in water-treatment processes. The status and properties of major chemical impurities in natural Fh is however still scarcely documented. Here we investigated the structure of aluminum-rich Fh, and their role in arsenic scavenging in(More)