Cyclic aqueous carbonation of fly ash in seawater: Enhancing carbonation efficiency and CO2 removal rate

Aqueous mineral carbonation of coal fly ash (CFA) is an effective CO₂ sequestration strategy, but improving its efficiency remains challenging. We observed a significant drop in carbonation efficiency from 94.8 % to 26.5 % when transitioning from an open to a sealed system using the same CaO-content CFA and seawater under ambient conditions. Experiments revealed that the slightly elevated pCO₂ in the sealed system accelerated CaCO₃ formation on CFA surfaces, hindering CaO leaching. To address this, we proposed introducing excess CO₂ post-carbonation to dissolve external CaCO₃, facilitating further CaO leaching and enhancing efficiency through a cyclic carbonation method. After optimizing the process with this cyclic approach, under identical conditions, the carbonation efficiency increased from 26.5 % (cycle 1) to 31.3 % (cycle 3) and CO₂ removal rate from 65.6 % to 80.3 %. Optimized solid-to-liquid and magnesium-to-calcium ratios during the cycles further improved efficiency. These findings provide valuable insights for enhancing industrial carbonation and CO₂ capture.