Visible-light photocatalysis accelerates As(III) release and oxidation from arsenic-containing sludge

•Visible-light photocatalysis accelerates the dissolution of arsenic sulfide sludge.•Visible light increases the oxidation rate of the released As(III) into As(V).•The sludge quickly precipitates in solution by phase-transforming into sulfur.•Both O2¯ and OH control the dissolution and oxidation of the sludge.•The intermediate sulfur species and sulfur radicals affect the fate of the sludge.