In situ mechanochemical activation of reduced iron powder for arsenic stabilization in high content arsenic sulfide sludge

Arsenic sulfide slag (ASS) with high content of arsenic is a common industrial waste in nonferrous metal smelting. Because of the high potential of arsenic leaching under environmental conditions, it brings serious ecological threat during storage. Stabilization of the unstable arsenic in ASS is urgently needed for its safe disposal. Current stabilization methods such as hydrothermal treatment, stabilization/solidification, and thermal copolymerization still face challenges including high energy consumption, poor stabilize efficiency and large volume increase after treatment. Here we developed a mechanochemical strategy to stabilize the bleachable arsenic using reduced iron powder as stabilizer. The arsenic leaching concentration was decreased from 18484.9 mg /L to only 56.3 mg/L after treatment, achieving a stabilization efficiency of 99.7 %. The mechanism study proved that MC treatment triggered the corrosion of Fe powder and dissolution of As2O3 with the help of acidic water in the ASS. An integration of the rapid reduction and oxidation then happened for the soluble arsenic. The produced As(II) and As(V) reacted with sulfide and iron oxides, greatly reducing the arsenic leaching concentration. The BCR sequential extraction results further conformed most of the arsenics (83.7 %) in ASS were stabilization into the environmental stable residual fraction.