Lime enhanced gasification (LEGS) process based on calcium looping in which CaO is employed as CO2 sorbent is an emerging technology for hydrogen production and CO2 capture. In this work, carbide slag which was an industrial solid waste was utilized as CO2 sorbent in hydrogen production process. Modification of carbide slag by propionic acid was proposed to improve its reactivity. The CO2 capture behavior of raw and modified carbide slags was investigated in a dual fixed-bed reactor (DFR) and a thermo-gravimetric analyzer (TGA). The results show that modification of carbide slag by propionic acid enhances its CO2 capture capacity in the multiple calcination/carbonation cycles. The favorable carbonation temperature and calcination temperature for modified carbide slag are 680-700 degrees C and 850-950 degrees C, respectively. Prolonged carbonation treatment is beneficial to CO2 capture of raw and modified carbide slags. The prolonged carbonation for 9 h in the 21st cycle increases the conversions of raw and modified carbide slags in this cycle. And then the carbonation conversions of the two sorbents were also improved in the subsequent cycles. Calcined modified carbide slag shows more porous microstructure compared with calcined raw one for the same number of cycles. Modification of carbide slag by propionic acid increases the surface area, pore volume and pore area. In addition, the volume and area of the pores in 20-100 nm in diameter were improved, which had been proved to be more effective to capture CO2. The microstructure of calcined modified carbide slag favors its higher CO2 capture capacity in the multiple calcination/carbonation cycles. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.