Effect of calcination temperature and atmosphere on pozzolanic activity and carbon fixation of flotation tailings

The thermal activated flotation tailings are an ideal raw materials for the preparation of cementitious materials, but the carbon emission caused by thermal activation greatly limits their green resource utilization. The prerequisite of large-scale industrialization of tailings are to effective reduction of carbon emissions due to the thermal activation while increasing pozzolanic activity is a prerequisite for large-scale industrialization of tailings. It used pure CO₂ atmosphere instead of the component of CO₂ in flue gas. The feasibility of the tailings activated in flue gas meantime the CO₂ fixation was discussed. Through the comparison of tailings activated at Air atmosphere with that of CO₂ atmosphere, the effect of activation and carbon fixation on the pozzolanic activity and capacity of carbon fixation of activated tailings was analyzed. XRD, N₂ adsorption and TG were used to analyze the physicochemical structure and carbon fixation performance of the tailings after two kinds of atmospheres activation and carbon fixation. The pozzolanic activity of the activated carbon fixation tailings were evaluated using the compressive strength of the stone after mixing the tailing with cement as an index. By studying the physicochemical structure of stones at different curing ages, the mechanism of the influence of carbon fixation on the hydration process of tailings-cement were revealed. The results show that the pozzolanic activity of the coal calcined in Air atmosphere is higher than that of the coal calcined in CO₂ atmosphere. The optimal activation temperature of tailings under Air and CO₂ atmosphere is 700℃, and the contribution of pozzolanic activity is 29.98% and 15.51%, respectively. After standard curing for 28 days, the compressive strength of tailings-cement stone calcination under Air and CO₂ atmosphere is 29.1% and 6.9% higher than that of raw coal-cement stone. At the same time, the tailings achieves the best carbon fixation effect at 700℃ under CO₂ atmosphere, and the carbon fixation rate is 0.93%. The tailings calcined in CO₂ atmosphere participates in cement hydration reaction, and the active substances and mineralization product CaCO₃ positively promote the hydration of clinker and production of ettringite (AFt). In the late hydration stage, the specific surface area of the hardened pastes increased and the pores filled, which improved the porosity density, and the compressive strength of the hardened pastes increased significantly.