Resource utilization of the CaSO₄ industrial byproduct as oxygen carrier (OC) in chemical looping combustion (CLC) is of great significance due to its attractive advantages including easy availability, low cost, large oxygen content as well as great potential to avoid the environmental harms during storage. But the gaseous sulphur released from the CaSO₄ side reactions is always a great concern, which not only deteriorates the reactivity of CaSO₄ but also causes pollution to the environment.
In order to improve the reactivity of CaSO₄ as well as efficiently control the gaseous sulphur emission from the CaSO₄ side reactions, a novel CaSO₄-CuFe₂O₄ mixed OC of special “core-shell” structure was firstly prepared using the novel template combined preparation method. Its reaction characteristics with a typical lignite was evaluated and the particular combined oxygen transfer mechanism involved was revealed, wherein both the CuFe₂O₄ (Fig 1) and the substrate CaSO₄ transfer their lattice oxygen in sequence firstly and then the reduced Cu and Fe₃O₄ would further in situ regain the lattice oxygen from the substrate CaSO₄ and transfer their recovered oxygen again to coal. And thus, the greatly enhanced reactivity (Fig 2) of this CaSO₄-CuFe₂O₄ mixed OC was reached as expected for sufficient conversion of coal, and the CO₂ yield was greatly improved as shown in Fig 3. 
Furthermore, the sulphur transformation and redistribution during the CaSO₄ mixed OC reaction with coal was studied in detail. Complete analysis of the sulphur species indicated that there existed great potential to directionally fix the gas sulphur released from the side reactions of CaSO₄ as solid sulphides and thus realized the in-situ desulphurization.
   Overall, the mixed OC of CaSO₄-CuFe₂O₄ OC possessed good reactivity and directional fixation of the gaseous sulphur, which benefited simultaneous carbon capture and in-situ desulfuration in CLC, as such was quite attractive in the future application.
 

Chemical looping combustion; CaSO4-CuFe2O4 mixed OC; template combined preparation method; oxygen transfer mechanism; Simultaneous carbon capture and sulfur removal;