Valorization of industrial carbide slag via microwave processing: A low-cost route to high-performance CaO-based CO2 sorbents.

Carbide slag, a high-calcium byproduct of acetylene production, presents significant environmental and land-occupation challenges due to limited recycling pathways. While converting this slag into calcium oxide-based CO2 adsorbents offers a promising valorization route, traditional thermal activation is often hindered by high energy requirements exceeding 800 °C and a reliance on chemical templates. To address these limitations, this study proposes an energy-efficient, zero-chemical microwave-assisted restructuring strategy for the sustainable valorization of carbide slag. By leveraging the dielectric response of the waste matrix, microwave irradiation triggers rapid volumetric dehydroxylation via an inside-out heating mode. This internal heating mechanism facilitates the development of a well-distributed mesoporous architecture while mitigating the premature surface sintering typically associated with conventional surface-to-core thermal gradients. Under optimized conditions at 500 °C for 30 min, the resulting microwave-modified adsorbent exhibited a CO2 adsorption capacity of 11.30 mmol g-1, representing a ∼104% increase compared to conventionally calcined slag. Kinetic analyses revealed that the microwave-engineered structure significantly lowers the carbonation activation energy from 11.94 to 7.67 kJ mol-1, effectively extending the kinetically-controlled reaction stage. Furthermore, Density Functional Theory calculations, corroborated by quantitative XRD and HRTEM characterization, identified the CaO (200) crystal plane as the preferentially exposed and most reactive surface, with a calculated adsorption energy of -1.705 eV at the O-top site. These findings establish a pragmatic and low-carbon pathway for the large-scale industrial valorization of carbide slag, offering a synergistic solution for solid waste management and carbon capture.