Ca(OH)2-Modified White Mud Sorbent with Enhanced Performance for SO2 Removal from Flue Gas

The efficient utilization of industrial waste (containing alkaline compounds, especially Ca-based species) for flue gas desulfurization (FGD) is of great importance for both environmental protection and resource recovery. In this study, paper industry white mud was modified with Ca(OH)2 to develop a cost-effective sorbent with enhanced SO2 removal performance. Optimization experiments identified the best preparation conditions as a 1:1 Ca(OH)2/white mud ratio, 60 °C modification temperature, 6 h reaction time, and a liquid-to-solid ratio of 3:1. Under these conditions, the sorbent achieved nearly 100% SO2 removal in the first 6 h and maintained >90% efficiency after 10 h, significantly outperforming raw white mud and Ca(OH)2 alone. Characterization revealed that the superior performance originated from structural stability and abundant active sites. BET analysis showed a high surface area (24.8 m2·g−1) and pore volume (0.160 cm3·g−1), which were largely preserved after desulfurization, indicating resistance to pore blockage. SEM images confirmed a transition from porous aggregates to densified product layers, consistent with a shrinking-core/product-layer mechanism. XRD identified CaSO4·2H2O as the dominant product, while in situ FTIR demonstrated that O2 promotes sulfite oxidation and H2O accelerates hydrated sulfate formation, enhancing activity but causing faster pore blocking. The presence of NO extended sorbent durability by catalyzing continuous sulfite oxidation through NO/NO2 redox cycling. Overall, Ca(OH)2-modified white mud combines high reactivity, durability, and structural stability, offering a promising alternative to conventional sorbents. This work provides a viable route for the resource utilization of paper industry waste and practical insights for designing efficient and sustainable materials for industrial FGD systems.