One-pot synthesis of regenerative calcium counterions from waste chicken eggshells for SO2-to-sulfur reduction

Abating sulfur dioxide (SO2) emissions is increasingly critical for addressing environmental concerns and safeguarding human health. In this study, we propose a novel, sustainable approach utilizing in situ eggshell waste-derived calcium-based materials for the catalytic thermal reduction of SO2 to elemental sulfur. Our research focuses on the facile synthesis of calcium-based compounds, proceeding from chicken eggshells to CaO, CaSO4, and finally CaS, for treating hazardous SO2 gas in a one-pot reactor. The effects of gas hourly space velocity (GHSV), temperature, and catalyst stability were studied. Optimal conditions for sulfur yield (71.32%) and SO2 conversion (43.38%) were achieved at 800 °C with a GHSV of 117 L h/g. Our findings demonstrate that the calcium-based materials exhibit exceptional stability, maintaining activity for 6.5 h. Mechanistically, the synergistic pathways of Mars-Van Krevelen and Eley-Rideal mechanisms underlying the SO2 reduction process were elucidated. This research presents a sustainable solution for converting SO2 into a valuable sulfur commodity, and contributes to achieving Sustainable Development Goal No. 12 on Sustainable Consumption and Production. By harnessing CaS derived from eggshell waste, our work underscores the potential for environmentally friendly practices in addressing industrial emissions and advancing sustainable resource utilization.