科研成果详情

Oxidation of As-III by three types of manganese oxide minerals affected by goethite was investigated by chemical analysis, equilibrium redox, X-ray diffraction (XRD) and transmission electron microscopy (TEM). Three synthesized Mn oxide minerals of different types, birnessite, todorokite, and hausmannite, could actively oxidize As-III to As-V, and greatly varied in their oxidation ability. Layer structured birnessite exhibited the highest capacity of As-III oxidation, followed by the tunnel structured todorokite. Lower oxide hausmannite possessed much low capacity of As-III oxidation, and released more Mn2+ than birnessite and todorokite during the oxidation. The maximum amount of As-V produced during the oxidation of As-III by Mn oxide minerals was in the order: birnessite (480.4 mmol/kg) > todorokite (279.6 mmol/kg) > hausmannite (117.9 mmol/kg). The oxidation capacity of the Mn oxide minerals was found to be relative to the composition, crystallinity, and surface properties. In the presence of goethite oxidation of As-III by Mn oxide minerals increased, with maximum amounts of As-V being 651.0 mmol/kg for birnessite, 332.3 mmol/kg for todorokite and 159.4 mmol/kg for hausmannite. Goethite promoted As-III oxidation on the surface of Mn oxide minerals through adsorption of the As-V produced, incurring the decrease of As-V concentration in solutions. Thus, the combined effects of the oxidation (by Mn oxide minerals)-adsorption (by goethite) lead to rapid oxidation and immobilization of As in soils and sediments and alleviation of the As-III toxicity in the environments.