Carbonation Conversion Rate Investigation of Alternative Low-Cost and Sustainable Calcium-Based Waste through a Carbonation/Calcination Process toward Carbon Dioxide Capture

Calcium-based waste (CBW) is potentially utilized as a sorbent in carbon dioxide (CO₂) capture through a calcium looping process. In this work, the carbonation conversion rates of eggshell and seashell were investigated at carbonation temperatures of 600−700 °C and CO₂ concentrations at 15−100 vol %, along with the carbonation/calcination cyclic test. The characteristics (morphology, elements, structures, and functional groups) of the CBW were observed in the optimum carbonation (3 h, 650 °C, 100 vol % CO₂) and calcination (1 h, 850 °C, air) conditions. From the findings, the optimal carbonation conversion conditions were observed at 650 °C (carbonation conversion rates, eggshell: 0.92, seashell: 0.80) and 15 vol % (carbonation conversion rates, eggshell: 0.86, seashell: 0.61). A continuous decrease in the carbonation conversion rate during the 10 cycles of carbonation/calcination demonstrated a progressive sintering phenomenon. FESEM, FIB, and EDS demonstrated that CO₂ was adsorbed on both the surface and inside of CBW after carbonation. XRD and FTIR displayed that the eggshell and seashell exhibited a dominant calcite and aragonite phase, respectively. Two potential carbonation conversion mechanisms were proposed: (i) a straightforward carbonation conversion mechanism of eggshell, which includes the rapid kinetic-controlled and diffusion-controlled reaction, and (ii) intricate multiple reactions and steps due to the presence of water in seashell, which leads to a slower carbonation conversion process.