The rate-limiting step during catalytic decomposition of thiosulfate by pyrite was studied in detail in this paper. The results show that Co and Ni impurities in synthetic pyrite increase thiosulfate decomposition, but F impurities in synthetic pyrite reduce thiosulfate decomposition. Density functional theory (DFT) showed that Co and Ni impurities increase the pyrite (100) surface Fermi energy and reduce its work function. This allows oxygen to accept electrons more easily, thus accelerating thiosulfate decomposition. Accordingly, Co or Ni impurities in pyrite make the O-O bond adsorbed on pyrite (100) surfaces become longer. On pyrite (100) surfaces doped with F, the O-O bond length decreases. These experimental results demonstrate that the rate-limiting step is the electron accepting step of oxygen during thiosulfate decomposition on the pyrite surface. (C) 2017 Elsevier B.V. All rights reserved.