Abstract The CO2 capture behavior of carbide slag as industrial waste dumped from a chlor-alkali plant in calcination/carbonation cycles was investigated in a fixed-bed reactor and a thermogravimetric analyzer, which was furthermore compared with that of hydration of CaO (Hy-CaO) and limestone. The main component of the carbide slag was the same as that of Hy-CaO which was Ca(OH)2. The effects of reaction temperature, particle size and cycle number on CO2 capture of the carbide slag were discussed. The carbide slag exhibited greater ultimate carbonation conversion than Hy-CaO and the limestone for the same number of cycles. For the same number of cycles, the calcined carbide slag had a smaller volume of pores 155 nm in diameter than the two other calcined sorbents. This was maybe a reason why the carbide slag exhibits a higher ultimate carbonation conversion than the Hy-CaO and the limestone. The cyclic carbonation conversion of the carbide slag was lower than that of the limestone before a certain time (called transition time); however, the converse result was observed after that time. It was attributed to the difference in the volume of pores