Leaching Behaviors of Arsenic from Arsenic-Iron Hydroxide Sludge during TCLP

Abstract

The toxicity characteristic leaching procedure (TCLP) is normally used to evaluate if sludge should be managed as hazardous waste. This study examines immobilization mechanisms of arsenic onto arsenic-iron hydroxide sludge, the byproduct of arsenic removal by coagulation with ferric chloride. The leaching mechanism of arsenic from the sludge due to the TCLP is also investigated. Microscopic characterization techniques including scanning electron microscopy equipped with energy dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR) were employed to characterize the sludge samples with the As-to-Fe ratios of 0.07 to 0.15 before and after the TCLP. SEM-EDS and FT-IR results suggested that arsenic-iron hydroxide sludge be ferric hydroxide, whose surface is inner or outer spherically sorbed by arsenic, rather than the precipitate of insoluble iron-arsenic compounds such as Fe(AsO )4 . This is also confirmed by XRD results, which revealed that none of suc...