Enhanced As(III) Sequestration Using Sulfide-Modified Nano-Scale Zero-Valent Iron with a Characteristic Core–Shell Structure: Sulfidation and As Distribution

Abstract

Sulfide-modified nano-scale zero-valent iron (S-nZVI) was synthesized and employed for the removal of aqueous As(III). The structure and removal performance of S-nZVI was investigated and compared with that of pristine nZVI. S-nZVI has an optimal As removal capacity of 240 mg/g, which is much higher than that of nZVI. The sulfidation of nZVI also enhanced the As(III) removal rate, and the enhancement largely depended on the S/Fe molar ratio. The optimum pH for As(III) removal with S-nZVI was in a broad range from 3 to 8. Transmission electron microscopy (TEM) with energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM) with EDS, and X-ray photoelectron spectroscopy (XPS) were employed to characterize the S-nZVI before and after reacting with As(III). The results demonstrated that S-nZVI had a unique core–shell structure. Sulfur was incorporated into the shell of S-nZVI, and the thickness of the surface layer increased from 5 nm to approximately 30 nm, which suggested that more As(II...