| Arsenic is a metalloid element existing commonly in soil, waters and organism.Arsenic is characterized by the strong toxicity, harm, carcinogenicity, mutagenicity andteratogenicity. The prevention and treatment of arsenic is a key research direction in theworld. It is significant of the effect of adsorption-desorption and oxidation-reduction toarsenic removing and transforming in nature. This effect is becoming the key method usedfor arsenic pollution treatment of soil or waters currently The iron oxide minerals havesome features like high specific surface area, oxidizing, etc, thus through adsorption-desorption of arsenic and the oxidation state can be effectively fixed water solublearsenic,it can play a an important role for treatment of arsenic contained in wastewater orsoil. This study take selects goethite and ferrihydrite to study the characteristic ofadsorption,desorption and oxidation mechanism and explore the influence of pH,phosphate and organic acids on the arsenic adsorption-oxidation.1.With initial arsenic concentration increasing, the adsorption amount of the differentforms of arsenic on iron oxides minerals gradually increase while the adsorption capacitygradually decrease. Under normal temperature conditions, two different kinds of iron oxideminerals (goethite, ferrihydrite) both have ability to adsorb As (Ⅲ),and arsenic adsorptionon different iron oxides minerals fits Freundlich well. The adsorption capacity follows:ferrihydrite> goethite, two kinds of iron oxide minerals adsorption of As (Ⅲ) are thepreferential adsorption. As the As (Ⅲ) initial concentration increasing, the desorptionquantity of arsenic on iron oxides minerals gradually increase, but the desorption quantityof As (Ⅲ) on the surface of the two minerals is small, and the desorption phenomenon isnot obvious. As the As (Ⅲ) initial concentration increasing, the oxidation quantity ofarsenic on iron oxides minerals gradually increase while the oxidation rate decrease.concentration increasing, the oxidation quantity of arsenic on iron oxides mineralsgradually increase while the oxidation rate decrease.2. As the pH increasing, the oxidation quantity of arsenic on iron oxides mineralsincrease in weakly acidic to neutral range, the adsorption capacity of As (Ⅲ) reaches amaximum at pH8and9on goethite and ferrihydrite. Two kinds of minerals in the neutralto slightly alkaline pH is within the scope of adsorption-oxidation effect is moreobvious,and the effect of pH on As (Ⅲ) adsorption by goethite and ferrihydrite lead to thesame trend. the oxidation volume of As (Ⅲ) on iron oxide minerals surface increase rapidly after the first showing a decreasing trend with the change of pH while the oxidationrate remained basically unchanged.3. Phosphate has competition with the adsorption of As (Ⅲ) in the iron oxide mineralssurface, and the inhibition increased with the increase of phosphate concentration. As (Ⅲ)adsorption decreases with P/As increasing when the initial concentration of As (Ⅲ) keepunchanged, As (Ⅲ) adsorption gradually increases as the initial concentration increasingwhen P/As keep unchanged. The affect of Three kinds of phosphate on As (Ⅲ) in the ironoxide mineral surface follow as: PO43-＞HPO42-＞H2PO4-.With the addition ofphosphate concentration increases, the amount of oxidation and oxidation rates were testeddecreasing trend.4. Organic acids play an inhibitory effect to As (Ⅲ) adsorption reactions on ironoxide minerals. The adsorption capacity and rate of As (Ⅲ) in the iron oxide mineralsdecline significantly with increasing concentration of organic acids, the affect of organicacids on As (Ⅲ) in the iron oxide mineral surface follow as: citric acid＞oxalic acid. Theamount of oxidation and the oxidation rate decreases as the concentration of organic acidsincreasing, and the effects of oxidation reactions by oxalic acid greater than citric acid. Theeffect of As (Ⅲ) oxidation on ferrihydrite by organic acids is greater than goethite. |
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