BACKGROUND Zero-valent iron (ZVI) is an environmentally friendly and cost-efficient material for the removal of contaminants. However, its application is challenged by problems such as surface passivation and pH increase in the reaction media. As a potential solution for this problem, pyrite, a waste of the mining industry, was used together with ZVI for reductive removal of azo dyes. RESULTS In comparison with ZVI alone, the ZVI/pyrite mixture showed dramatically enhanced efficiency and reusability for dye removal, although pyrite itself can hardly remove dyes. The reaction rate constant k(obs) for the removal of Orange II at the initial pH (pH(0)) of 7.0 was enhanced 9.4- to 28.0-fold by using the mixture at a pyrite/ZVI mass ratio ranging from 1 to 4, respectively. The mechanism studies indicate that pyrite not only helped produce more iron(II) by facilitating iron corrosion and the iron(II)/iron(III) cycle in the mixed system, but also activated the ZVI surface by in situ sulfidation. The high reactivity of the adsorbed iron(II) in the mixed system significantly contributed to dye removal, especially at the alkalescent pH. CONCLUSION Pyrite accelerated the reductive removal of dyes by ZVI, through inhibiting its surface passivation and suppressing the pH increase in the reaction media. Therefore, this research proposes a facile method for enhancing the reactivity and applicability of ZVI in environmental remediation. (c) 2020 Society of Chemical Industry