This paper presents a facile approach to selectively decrease the CaO content in titania slag from 1.09 to 0.18 wt.% under a selective chlorination atmosphere of Cl-2 and CO. Thermodynamic analysis indicated that a predominance area exists to selectively chlorinate CaO with a low reduction potential. The intrinsic chlorination kinetics indicated that both the high partial pressure of chlorine and high temperature were advantageous to increase the chlorination selectivity,of CaO. Under the guidance of the thermodynamic and intrinsic kinetics, selective chlorination kinetics of CaO from titania slag were conducted at 1173-1273 K and were represented by the pore-blocking rate law. The present study indicated that a high concentration of reactant gases with a low reduction potential at high temperature could simultaneously overcome the inner mass transfer resistance while maintaining a high chlorination selectivity. The optimized partial pressures of Cl-2 and CO were 0.8 and 0.2 atm, respectively, and the temperature was 1273 K. (C) 2016 Elsevier B.V. All rights reserved.