The catalytic activities of iron concentrate, rare earth concentrate, and rare earth tailings for semi-coke denitration were studied using thermogravimetric analysis combined with Fourier transform infrared spectroscopy. The results revealed that less NO was produced from semi-coke combustion with the addition of iron and rare earth minerals, and meanwhile CO production was reduced as well. It is likely that the addition of iron and rare earth minerals enhances the homogeneous reduction of NO by CO thus improving the removal efficiency of nitrogen oxides. The catalytic activity of rare earth tailings was higher than those of rare earth concentrate and iron concentrate. It is evidenced that ferric oxide and rare earth oxides in the tailings are associated, synergically catalyzing the homogeneous reduction of NO by CO.