Simultaneous oxidation and adsorption of arsenic by one-step fabrication of alum sludge and graphitic carbon nitride (g-C3N4).

The oxidation of trivalent arsenic (As(III)) to pentavalent arsenic (As(V)) is a common pretreatment to remove As(III) from the aqueous phase. The graphitic carbon nitride as a photocatalyst can transform As(III) to As(V), but the photocatalyst does not adsorb any species of arsenic. In this study, a new composite material to achieve the simultaneous oxidation and adsorption of arsenic was synthesized by co-pyrolyzing alum sludge and melamine. It was hypothesized that graphitic carbon nitride derived from melamine oxidizes As(III) to As(V) and pyrolyzed alum sludge provides strong adsorption sites for the oxidized As(V). The composites were characterized by X-ray diffraction, Brunauer-Emmett-Teller(BET) surface, scanning electron microscope, and X-ray photoelectron spectrometer. The composite material effectively converted As(III) to As(V) under the light, and the total arsenic concentration decreased in the aqueous phase via the adsorption of As(V). Speciation analysis of arsenic on the composite showed that both As(III) and As(V) species were present on the surface of adsorbent, from which desorption by mixing with deionized water was difficult. This new and green composite material can oxidize As(III) and adsorb arsenic simultaneously under the light, which can be used to treat arsenic-containing water.

Effects of lead mineralogy on soil washing enhanced by ferric salts as extracting and oxidizing agents.

In this study, we evaluated the feasibility of using ferric salts including FeCl3 and Fe(NO3)3 as extracting and oxidizing agents for a soil washing process to remediate Pb-contaminated soils. We treated various Pb minerals including PbO, PbCO3, Pb3(CO3)2(OH)2, PbSO4, PbS, and Pb5(PO4)3(OH) using ferric salts, and compared our results with those obtained using common washing agents of HCl, HNO3, disodium-ethylenediaminetetra-acetic acid (Na2-EDTA), and citric acid. The use of 50 mM Fe(NO3)3 extracted significantly more Pb (above 96% extraction) from Pb minerals except PbSO4 (below 55% extraction) compared to the other washing agents. In contrast, washing processes using FeCl3 and HCl were not effective for extraction from Pb minerals because of PbCl2 precipitation. Yet, the newly formed PbCl2 could be dissolved by subsequent wash with distilled water under acidic conditions. When applying our washing method to remediate field-contaminated soil from a shooting range that had high concentrations of Pb3(CO3)2(OH)2 and PbCO3, we extracted more Pb (approximately 99% extraction) from the soil using 100 mM Fe(NO3)3 than other washing agents at the same process conditions. Our results show that ferric salts can be alternative washing agents for Pb-contaminated soils in view of their extracting and oxidizing abilities.