Preparation, Characterization Of Fe-oxyhydroxide-montmorillonite Complexes And Their Arsenate-adsorption Behaviour

In tropical and sub-tropical area, soil solution contains large amount of hydroxy-Fe ions. These hydroxy-Fe ions may react with montmorillonite in soils to form Fe-oxyhydioxide-monUiiorillonite complexes. Such complexes might have affinity for detrimental inorganic oxyanions such as arsenate, a common toxic contaminant in soils. The purpose of this study is to investigate the influence of environmental conditions on the adsorption of arsenate on Fe-oxyhydroxide-monlmorillonte complexes, which is significant to agrology, geochemistry and environmental science.Fe-oxyhydroxide-monlmorillonite complexes were prepared by reaction of purified Ca-montmorillonite with hydroxy-Fe solution, and characterized by chemical analysis, electron microprobe (EPMA), powder x-ray diffraction (XRD), differential thermal analysis (DTA), Mossbauer spectroscopy, x-ray Photoelectron Spectrum (XPS), Zeta potential, etc. Characterization shows that the prepared complexes are mainly composed of montmorillonite and their surface-deposited Fe oxyhydroxide. They have different properties from montmorillonite and Fe oxyhydroxides such as larger specific area, different surface potential, etc.Under the acidity, temperature and other conditions ( initial arsenate concentration, ion strength, duration of adsorption) simulated to that of soil in tropical and sub-tropical area, the adsorption of arsenate on the prepared Fe-oxyhydroxide-montmorillonite complexes were conducted. The correlations between the arsenate uptake ability of Fe-oxyhydroxide-montmorillonite complexes and the duration of adsorption, initial concentration of arsenate, ion strength of the solution, acidity and temperature of environment are investigated and compared to the adsorption of arsenate on to montmorillonite and Fe oxyhydroxide. Results stow that Fe-oxyhydroxide-montmorillonite complexes have a strong affinity for arsenate species under experimental conditions, which is supposed to influence the behavior of arsenate in soil. On the basis of the analysis, the possible mechanism of arsenate adsorption is also discussed.