Abstract
Carbon capture and storage (CCS) is a promising technology for mitigating CO(2) emissions, and Ca-based adsorbents are regarded as potential candidates for CO(2) capture. This study focuses on the synthesis of Ca-based adsorbents using an aluminum (Al) leaching residue from coal ash. Through hydrothermal treatment of the Al leaching residue, tobermorite with a high Ca ratio was synthesized. By employing CO(2)-pressurized leaching followed by calcination at 900 °C, the fibrous SiO(2)-modified CaO structure was synthesized. The synthesis of SiO(2)-modified CaO and its CO(2) absorption property were investigated by TG (Thermogravimetry), SEM (Scanning Electron Microscopy), ICP (Inductively Coupled Plasma), and TEM (Transmission Electron Microscopy). The conversion of SiO(2)-modified CaO was 93.8% during the first CO(2) adsorption, and the CaO conversion rate can still be maintained at 70.3% after 10 cycles. In comparison, pure CaO exhibited only a 42.9% conversion rate after 10 cycles. Due to the inhibiting effect of SiO(2) on sintering, the synthesized SiO(2)-modified CaO showed a higher CO(2) absorption amount after 10 cycles. After 15 cycles, the absorption amounts of pure CaO and Ca-based adsorbents were 30.7 and 32.5 g of CO(2)/(100 g of absorbent), respectively. After cycling, SiO(2)-modified CaO still had a fibrous structure, and it had a smaller diameter and higher specific surface area than pure CaO. The special structure of tobermorite can inhibit the sintering of SiO(2)-modified CaO and improve its cyclic stability in the process of CO(2) absorption at high temperature. The synthesis of SiO(2)-modified CaO by using the Al leaching residue of coal ash offers novel approaches for treating coal-based wastes containing significant amounts of Ca and Si.