The degradation of p-chloroaniline (PCA) in aqueous solution by pyrite was studied. The effects of different parameters such as pyrite particle size, pH and pyrite dosages on the degradation of PCA were examined in batch experiments. The rate of PCA degradation increased with increased pyrite dosage and with decreased pyrite particle size from 20 to 200 mesh in aqueous solutions. Results showed that PCA degradation accelerated with lowering initial pH. In addition, the efficacy of PCA degradation by pyrite was higher with oxygen presence as compared to without oxygen. The role of reactive oxygen species (ROS) produced by pyrite in the system was also investigated. In particular, superoxide radical (Or) produced by pyrite was instrumental in producing more H2O2, which favored the degradation reaction. The results of this study give new insights into the mechanism of the reactivity of pyrite toward environmental contaminants. (C) 2015 Elsevier B.V. All rights reserved.