Effect of Na2CO3, HF, and CO2 Treatment on the Regeneration of Exhausted Activated Carbon Used in Sintering Flue Gas

The method of continuous treatment with Na2CO3 solution, HF solution, and CO2 was proposed for the regeneration of the exhausted activated carbon (EAC) produced in the sintering flue gas purification process. In order to obtain the optimal operation conditions, the effect of key parameters such as Na2CO3 solution concentration, HF solution concentration, and CO2 activation temperature on the sulfur conversion rate and regeneration efficiency was analyzed. Also, the N-2 adsorption, Brunauer-Emmett-Teller analysis, scanning electron microscopy-energy dispersive spectrometry, X-ray diffraction, X-ray fluorescence, and Fourier transform infrared spectroscopy were adopted to investigate the deactivation reason and the change of the physical-chemical properties. The results showed that the deactivated EAC was mainly due to the deposition of inorganic compounds such as CaSO4, SiO2, and KCl to block the pores. Continuous treatment with Na2CO3 solution and HF solution could remove the inorganic compounds effectively. CO2 activation treatment further developed the blocked porosity and decreased the surface acidity. The optimal conditions for the regeneration of EAC were a Na2CO3 concentration of 0.5 mol/L, an HF concentration of 0.8 mol/L, and a CO2 activation temperature of 1073 K with the activation time of 1 h, corresponding to the specific surface area of 607.91m(2)/g. In the fourth regeneration cycle, the adsorption performance during the successive adsorption-regeneration process could still maintain a high level and the regeneration efficiency was 95.31%.