Investigation on the cyclic CO2 capture behaviour and degradation mechanism of molten salt promoted MgO derived from commercial hydromagnesite

Abstract

This study examines the cyclic CO₂ capture performance and degradation mechanism of molten salt-promoted MgO, a low-cost and scalable precursor, derived from commercially available hydromagnesite. The material was modified using different nitrate-based molten salt compositions to enhance CO₂ uptake. Among the formulations, single- and double-salt-promoted MgO exhibited the highest initial capture capacities; however, performance declined with repeated cycling. Notably, the single-salt system demonstrated comparatively better stability over 10–22 cycles than others. The observed reduction in CO₂ capture capacity is attributed to the gradual loss and transformation of nitrate species, which reduces the effective molten phase and pore blockage. Thermodynamic analysis supports the conversion of active nitrate phases into less effective forms during cycling, while X-ray diffraction and ICP-MS confirm a decrease in nitrate content despite minimal change in overall sodium levels. These findings highlight the critical role of molten salt stability in sustaining CO₂ capture performance and provide insight into the design of more durable MgO-based sorbents.