Denitrification performance of rare earth tailings-based catalysts

Rare earth tailings from the Bayan Obo mine are rich in rare earth, iron, and other catalytically active substances. In this study, Na2CO3 and Ca(OH)2 were mixed with rare earth tailings, roasted, and the tailings modified by HCl-citric acid leaching and pickling to prepare high-performance rare earth tailings-based denitrification catalysts. Denitrification performance tests show that, in the temperature range 700°C~900°C, the alkali and acid co-processed modified tailings sample gave the best catalytic denitrification performance. XRD, SEM, and H2-TPR analyses show that, compared with raw ore samples, Fe activity sites increased after alkali and acid co-treatment. Cracks and holes appeared on the surface of the sample, and the reduction temperature range was broadened. XPS analysis showed that Fe coexisted in the forms Fe2+ and Fe3+, and Ce in the forms Ce3+ and Ce4+. At a rare earth tailings microwave roasting temperature of 500°C, NO concentration of 500 ppm, CO/NO ratio 4:1, and reaction temperature of 900°C, the denitrification efficiency of the catalyst was optimal, at up to 96.2%. In this study, a relatively green and pollution-free method was used to prepare catalysts, which can provide reference for solving the problem of rare earth tailings accumulation.