Distinctive Arsenic(V) Trapping Modes by Magnetite Nanoparticles Induced by Different Sorption Processes

• Published in: Environmental science & technology Vol. 45; no. 17; pp. 7258 - 7266
• Main Authors: Wang, Yuheng, Morin, Guillaume, Ona-Nguema, Georges, Juillot, Farid, Calas, Georges, Brown, Gordon E
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01-09-2011
• Subjects: Adsorption; Applied sciences; Arsenic; Arsenic - chemistry; Biological and physicochemical phenomena; Biological and physicochemical properties of pollutants. Interaction in the soil; Chemical Precipitation; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Environmental Processes; Environmental Sciences; Exact sciences and technology; Experiments; Ferric Compounds - chemistry; Magnetite Nanoparticles - chemistry; Microscopy, Electron, Transmission - methods; Models, Molecular; Nanoparticles; Natural water pollution; Oxidation-Reduction; Particle Size; Pollution; Pollution, environment geology; Soil and sediments pollution; Water treatment; Water treatment and pollution; X-Ray Absorption Spectroscopy - methods; Iron oxide; XANES spectrometry; Arsenic; Arsenates; Nanoparticle; X ray diffraction; Sorption; Trace element; Carcinogen; Trapping; Magnetite; Transmission electron microscopy; Poison; Nanostructured materials
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es200299f

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 precipitation, using X-ray absorption fine structure (XAFS) spectroscopy and transmission electron microscopy (TEM). XAFS results suggest that AsO4 tetrahedra form predominantly inner-sphere bidentate corner-sharing (2C) complexes and outer-sphere complexes on magnetite in the adsorption experiments. In the precipitation experiments, an increasing fraction of AsO4 tetrahedra appears to be incorporated in clusters having a magnetite-like local structure with increasing As loading, the remaining fraction of As being adsorbed at the surface of magnetite particles. In the sample with the highest As loading (15.7 μmol/m2) XAFS data indicate that As(V) is fully incorporated in such clusters. Such processes help to explain the significantly higher arsenic uptake in precipitation samples compared to those generated in adsorption experiments. In addition, for the precipitation samples, TEM observations indicate the formation of amorphous coatings and small (∼3 nm) nanoparticles associated with larger (∼20–40 nm) magnetite nanoparticles, which are absent in the adsorption samples. These results suggest that As(V) could form complexes at the surfaces of the small nanoparticles and could be progressively incorporated in their structure with increasing As loading. These results provide some of the fundamental knowledge about As(V)-magnetite interactions that is essential for developing effective water treatment technologies for arsenic.