| Arsenic is a naturally occurring toxic element, widely known for its toxicity even atlow concentrations, and is also introduced into environments through a number ofindustrial processes and agricultural practices, including mining, using of arsenicalpesticides and so on. It causes a variety of adverse effects to environment and humans.Developing efficient treatment and understanding arsenic behavior in environment aretherefore both major public health issues gaining increasing attention in recent years. Asessential source of Mn element for the nutrition of animals and plants, one of importantadsorbents, redox agents, catalysts and carriers for environmental information, Mn oxideminerals are important component in soil. They usually cement with clay mineral, whichis also important element in soil. Investigation on the oxidization characteristics of theirassociations will provide some insights into predicting the chemical reactions andremoval of arsenic in soil.In this paper, the preparation, characterization, and oxidation properties for As(Ⅲ)of manganese oxide coated clay were investigated. A scanning electron microscope(SEM), X-ray diffraction spectrum (XRD), Rapid potentiometric titration(RPT) andBET-N2 analyses were used to observe the surface properties of the coated layer. Theconclusion of the present study may be listed as follow:1) XRD patterns and SEM micrographs demonstrated that discrete kaolinite,montmorillonite, birnessite and todorokite had good characteristic diffractionpeaks, except the hydrous manganese oxide (HMO). The characteristic diffraction peaksof the associations nearly consisted with the discrete Mn oxide minerals, while the peakswere broadened and weakened. As the increase of the clay content, the characteristicdiffraction peaks of clay were gradually appeared and strengthened. The SEM/EDS forthe sample of manganese-coated clay were illustrated that manganese was spread over thesuface of coated sand.2) The zero point of charge (PZC) of birnissite, todorokite, HMO, kaolinite andmontmorillonite were 3.16, 3.28, 1.93, 3.87 and 4.18, respectively. The PZC of theassociations were between 2.05 and 3.79, and increased with the adding of the clay.3) The magnitude order of the outside surface area was (m2/g): HMO (207.2)＞todorokite (102.5)＞montmorillonite (40.9)＞birnessite (33.7)＞kaolinite (24.8). And theoutside surface area of the associations were between 28.2 and 184.6 m2/g. The orderillustrated that the outside surface area of HMO, todorokite and birnessite were largerthan kaolinite, while they were also higher than montmorillonite except birnessite. So the outside surface area of HMO-Kao (Mont) and Tod-Kao(Mont) associations weredecreased when the clay was increased, but the change of Bir-Mont association's outsidesurface area were opposite. The change of the outside surface area of Bir-Kao was little.In all, the outside surface area of all the associations were increased as compared to thespecific surface area of clay.4) The maximum amounts of As(Ⅲ) oxidized by the tested samples in order were(mmol/kg): birnessite (763.5)＞todorokite (645.9)＞HMO(602.9)＞montmorillonite(121.2)＞kaolinte (77.7). When the clay was cement with the Mn oxide minerals, the neworder was (mmol/kg): B-K03 (1992.5)＞B-M03 (1490.7)＞T-K03 (1280.0)＞T-M03(1157.1)＞H-K03(778.5). The maximum amounts of As(Ⅲ) oxidized byassociations were all larger than the discrete Mn oxide minerals, and the As(Ⅲ) removalrate increased with increasing clay, suggesting the clay was responsible for the adsorptionof the produced As(Ⅴ). The amounts of As(Ⅲ) oxidized by tested samples were increaedwith ion strength.
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