Deactivation of Ca-based sorbents by coal-derived minerals during multicycle CO2 sorption reactions at elevated temperature and pressure was investigated using a laboratory-scale horizontal-tube reactor. The sorbents tended to undergo a solid-solid reaction with coal-derived ash components such as silicon (Si) and aluminum (Al) during multicycle CO2 sorption with an intermediate hydration stage. This reaction formed complex inorganics, such as mayenite (Ca12Al14O33), calcium silicate (Ca2SiO4), and spurrite (Ca-5(SiO4)(2)CO3), and substantially decreased the sorbents' CO2 sorption ability. Interaction with the coal-derived minerals was significant during the multicycle calcination-carbonation reaction only when the sorbents were subjected to the intermediate hydration treatment. This result suggests that steam enhanced the solid-solid interaction between the minerals and the sorbents at elevated temperature (> 873 K) and pressure (6.0 MPa) and that the interaction should be avoided by selecting proper reaction conditions for efficient utilization of the Ca-based sorbents.