PH-dependent photochemical transformation of arsenic sulfide sludge catalyzed by Fe ions under visible light irradiation

• Fe(II) promoted the photo-oxidation of released As(III) in ASS. The mechanism Fe(II)-stimulated was pH-dependent. At pH 3.0, both OH and SO 4 − made a contribution to As oxidation. Reductive sulfur species from ASS played critical role Fe(II)/Fe(III) cycle. Arsenic sulfide sludge (ASS) is typical precipitation product acid smelting wastewater. Previous study reported that when exposed sunlight, release oxidation were markedly accelerated. However, key factor trigger photocatalytic transformation still unclear. Herein, we revealed coexisting ions promote under visible light. We further validated In conditions, by cycling catalysis with assistance reductive ASS, e.g. S 2− 3 , thus accelerated As(III). While neutral nascent ferric hydroxide colloids enhanced rate via photo-induced ligand-to-metal-charge transfer (LMCT) mechanism. These findings help predicting controlling fate real arsenic-containing sunlit environments.