Oxidation of As^Ⅲ by Several Manganese Oxide Minerals in Absence and Presence of Goethite

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 Asv, 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 hansmannite possessed much low capacity of As^Ⅲ oxidation, and released more Mn^2＋ than birnessite and todorokite during the oxidation. The maximum amount of Asv 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） 〉 hansmannite （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 Asv being 651.0 mmol/kg for birnessite, 332.3 mmol/kg for todorokite and 159.4 mmol/kg for hansmannite. Goethite promoted As^Ⅲ oxidation on the surface of Mn oxide minerals through adsorption of the Asv produced, incurring the decrease of Asv 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.

Metal Uptake by Plants from Soil Contaminated by Thin-Film Solar Panel Material

Various metals, including zinc (Zn), nickel (Ni), aluminum (Al), chromium (Cr), gallium (Ga), lead (Pb), copper (Cu) and indium (In), may be released and cause contamination when scrapped end-of-life (EoL) Cu(InGa)Se2 thin-film solar panel (CIGS TFSP) is buried in the soil. In this study, we grew Brassica parachinensis L. H. Bariley (VegBrassica) in three different types of soils, namely, a commercial soil, a Mollisol, and an Oxisol, which had been contaminated by CIGS TFSP to various extents. The concentrations of contaminants in these soils were positively correlated with both the amount of CIGS TFSP added and the burial period. Plants grew well in commercial soil and Mollisol, but those in Oxisol showed prominent signs of chlorosis and died after 30 days. The bioaccumulation factor (BF) and concentration of Zn in VegBrassica grown in commercial soil with 10% of CIGS TFSP added were 3.61 and 296 mg/kg, respectively, while the BF and concentration of In of VegBrassica grown in Mollisol were 3.80 and 13.72 mg/kg, respectively. The results showed that soils were contaminated by metals released from CIGS TFSP, and different adsorption patterns were observed for VegBrassica?depending on which types of metals associated with the soil properties.