The integrated CO2/sludge gasification using the waste heat in hot slags, was explored with the aim of syngas production, waste heat recovery and sewage sludge disposal. The results demonstrated that hot slags presented multiple roles on sludge gasification, i.e., not only a good heat carrier (500-950 degrees C) but also an effective desulfurizer (800-900 degrees C). The total gas yields increased from 0.022 kg/kg(sludge) at 500 degrees C to 0.422 kg/kg(sludge) at 900 degrees C; meanwhile, the SO2 concentration at 900 degrees C remarkably reduced from 164 ppm to 114 ppm by blast furnace slags (BFS) and 93 ppm by steel slags (SS), respectively. A three-stage reaction was clarified including volatile release, char transformation and fixed carbon using Gaussian fittings and the kinetic model was analyzed. Accordingly, a decline process using the integrated method was designed and the optimum slag/sludge ratio was deduced. These deciphered results appealed potential ways of reasonable disposal of sewage sludge and efficient recovery of waste heat from hot slags. (C) 2015 Elsevier Ltd. All rights reserved.