Steelmaking slag contains high amounts of CaO, Fe2O3, SiO2, and Al2O3, and has great potential as a catalyst for the tar-reforming reaction to produce a carbon composite and hydrogen. This paper describes chemical waste-heat recovery of tar and the effects of slag on the tar-reforming reaction. The results indicate that slag has a good activity for decomposing tar into the gas phase and for producing high carbon content within the slag. The introduction of coal-pyrolysis products to slag at a temperature of 500 degrees C caused an 18%vol increasing in the gas amount and a 6%mass enhancing in the carbon content within the slag compared to coal pyrolysis without slag. At higher temperatures, coal pyrolysis gave rise to lower carbon deposition within the slag but a higher amount of gas product. Moreover, the gas reforming reaction occurred simultaneously with tar decomposition at higher temperatures. This proposed system offers energy-saving benefits of 103 MJ/ton steel and a 6%mass reduction in coke-breeze usage in the steelmaking industry. (C) 2013 Elsevier Ltd. All rights reserved.