Assessment of waste hardened cement mortar utilization as an alternative sorbent to remove SO2 in flue gas

Developing efficient low-cost absorbents has been recognized as a prerequisite for industrial application of wet flue gas desulfurization (WFGD). Herein, hardened cement mortar (HCM) particles developed from waste concrete blocks were used as an innovative absorbent for SO2. The results show that the SO2 in flue gas can be completely absorbed by the highly alkaline HCM slurry. Under optimum operating conditions, 0.8 g of SO2 was retained by per gram of HCM. Under acid conditions produced upon dissolving SO2 in water, the Ca-rich compounds in HCM particles can continuously release Ca2+ and OH- into the HCM slurry. The Ca2+ ions released can effectively combine with SO32-, resulting in the absorption of SO2 dissolved in water. The dissolution process of HCM particles is well described by the pseudo-second-order model. The desulphurization byproduct was characterized by X-Ray diffraction (XRD) analysis, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and energy dispersive spectrometry (EDS). The results show that the desulphurization product mainly consists of gypsum. The technology developed provides a type of new material for removing SO2 in waste flue gas. It also offers an innovative solution for the disposal of waste concrete which is also a global environmental concern.