Arsenate immobilization associated with microbial oxidation of ferrous ion in complex acid sulfate water

► Arsenate immobilization upon microbial Fe2+ oxidation in acid sulfate water was investigated. ► The schwertmannite model was invalid for explaining the process in the complex acid sulfate water. ► Arsenate was initially removed through co-precipitation of non-Fe metals, arsenate and phosphate. ► Followed by formation of mixed Fe, arsenate and phosphate phases after sufficient Fe3+ was produced. ► The last step involved surface complexation with HAsO42− being the dominant adsorbed As species.