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

Abstract 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.