Adsorption Behaviors of Arsenic(V) onto Fe-Based Backwashing Sludge Produced from Fe(II)-Removal Plants
This study investigates the adsorption characteristics of As(V) onto the Fe-based backwashing sludge (FBBS), which was produced in the Fe(II) removal process. FBBS exhibits rough surfaces and shows high BET surface area of 148.41 m2/g. According to the results of EDS and XRD, the main constituents include sulfate inter-layered Fe hydroxide [Fe(SO4)OH], ferric oxhydroxide (γ-FeOOH), quartz (SiO2), and calcium carbonate (CaCO3). The adsorption kinetics data were well described by the Elovich model (r2 = 0.993), indicating the highly heterogeneous adsorption. The maximum adsorption capacity of As(V) increased from 40.04 to 88.76 mg/g as temperatures increased from 298 to 318 K, suggesting an endothermic process. The removal of As(V) was inhibited with elevated solution pH, especially from pH 7.0 to pH 10.0. Moreover, the removal of As(V) was enhanced with an increase in ion strength (0.01-1 M NaNO3), implying that the adsorption of As(V) was mainly through inner-sphere complexes mechanism.