A series of carbon dioxide gasification tests of waste biomass chars were performed in a thermogravimetric analysis system, at non-isothermal heating conditions. The effects of the inorganic constituents of the fuels on thermal conversion characteristics were examined. Reaction rates were determined by developing a power law model. The bulk of char gasification process occurred between 800 and 950 degrees C. Maximum reaction rate and conversion were exhibited by waste paper char, due to its higher surface area. Inherent alkaline and alkaline earth carbonates and sulphates acted as catalysts, by increasing the reactivity of the fuels in carbon dioxide and causing their degradation to start at lower temperatures (60-75 degrees C). The kinetic model fitted the experimental results accurately. Activation energy values and reaction order ranged from 180 to 370 kJ/mol and 0.4 to 0.6, respectively, among the chars, indicating a chemically controlled process. (C) 2010 Elsevier Ltd. All rights reserved.