Stabilization of arsenic sulfide sludge by hydrothermal treatment

Arsenic sulfide sludge (ASS) generated during the treatment of strongly acidic wastewater with sulfide precipitation method has long been a problem for the nonferrous smelting enterprises. In this study, stabilization of ASS from a lead and zinc smelter by hydrothermal treatment was investigated. The ASS was characterized with high contents of arsenic (46.9%) and sulfur (32.6%), and leaching concentration of arsenic was determined to be 702.0 mg/L. The parameters of the hydrothermal treatment were studied in detail. It was found that the leaching concentrations of As, Pb and Cd, dehydration ratio, density and morphology of ASS changed dramatically during the hydrothermal treatment. Comprehensive consideration of these changes, the optimal conditions were determined to be temperature of 200 °C, reaction time of 4 h, liquid-to-solid (L/S) ratio of 1:1 and the initial pH of 2. Under the optimal conditions, the leaching concentration of As for the treated ASS decreased to