Novel resource utilization approach of spent catalyst from flue gas denitrification: Preparing high quality titanium-bearing pellets

Spent titanium-based catalyst is a waste generated by the selective catalytic reduction (SCR) denitrification process, whose generation is dramatically increasing in the iron and steel industry year by year. A novel approach was proposed in this work to prepare titanium-bearing pellets by using spent catalyst. The influences of spent catalyst addition on the comprehensive properties of pellets were studied. The corresponding relationship between the change of phase structure and the spent catalyst pellets' strength was investigated. The results demonstrated that the spent catalyst could be adsorbed on the surface of ore particles physically and chemically, improving the adhesion of particles inside the pellet and the hydrophilicity, thus obtaining good comprehensive performance of the green pellets. When adding 5.0 wt% spent catalyst, the bentonite dosage could be reduced by 50%, and the strength of roasted pellets could meet the requirement of large blast furnaces. The consolidation mechanism of the spent catalyst pellets indicated that TiO2 reacted with FeO first to generate FeTiO3 in the preheating process and further oxidized to form Fe2TiO5 in the roasting process. The unreacted TiO2 would appear in the roasted pellets and inhibit recrystallization and polycrystalline growth of Fe2O3 grains, resulting in the reduction of compressive strength. Overall, high-quality titanium-bearing pellets could be obtained when the amount of spent catalyst was less than 5.0 wt%. This study thus provided an alternative route to resource utilization of spent catalysts in iron and steel enterprises.