Simultaneous oxidation of arsenic and antimony at low and circumneutral pH, with and without microbial catalysis

► At circumneutral pH As and Sb oxidation was catalyzed by microbes. ► At acid pH As and Sb are oxidized abiotically by Fe(III). ► At acid pH Fe(III) was formed by microbial oxidation. ► In abiotic Fe(III)-solutions, Sb oxidizes slightly faster than As. ► Oxidation rates increased by increasing As, Sb, Fe(III), and Cl with light.