Schwertmannite was synthesized through the oxidation of FeSO4 by Acidithiobacillus ferrooxidans LX5 cell suspension and characterized using X-ray diffraction spectroscopy (XRD) and scanning electron microscope (SEM). Schwertmannite photocatalytic degradation of acid orange 7 (AO7) assisted by citric acid was further investigated at different initial pH values and different concentrations of schwertmannite or citric acid. The results showed that it was difficult for AO7 to be discomposed by schwertmannite or citric acid alone under UV irradiation. However, the removal of AO7 was significantly enhanced when biogenic schwertmannite and citric acid coexisted in the reaction system. Low pH and high initial concentrations of citric acid and schwertmannite were beneficial to the degradation of AO7. Hydroxyl radical ((OH)-O-center dot) and Fe(II), the intermediates, were investigated during the reactions to reveal their correlation with the degradation of AO7. A possible mechanism for biogenic schwertmannite photocatalytic decomposition of AO7 in the presence of citric acid was proposed. (C) 2015 Elsevier B.V. All rights reserved.