Stabilization of arsenic sludge with mechanochemically modified zero valent iron.

Modified zero valent iron (ZVI) is obtained from commercial iron powder co-ground with manganese dioxide (MnO2) in intensive mechanical stress. The result indicates that the modified ZVI is very effective in arsenic sludge stabilization with a declination of arsenic leaching contraction from 72.50 mg/L to 0.62 mg/L, much lower than that of ordinary ZVI (10.48 mg/L). The involved process, including mechanochemical activation, corrosion and arsenic adsorption, is characterized explicitly to verify the improved arsenic stabilization mechanism. It shows that the mechanically formed Fe-Mn binary oxides layer results in an intensive corrosion extent, generating a mass of corrosion products. Moreover, as the emergence of Mn will restrain the process of iron (hydr)oxides crystallization, the ultimate corrosion products of the modified ZVI predominates in amorphous iron (hydr)oxides, performing much better in arsenic absorption. According to the BCR analysis, unstable arsenic in sludge is easily transformed to residual fraction by the help of amorphous iron (hydr)oxides, resulting in a restrained environmental availability of arsenic sludge after the modified ZVI stabilization.