The paper presents a model of the reaction between SO2 and trona based slurries. Experimental findings relevant to the desuffurisation in a spray dryer were compared with the proposed mathematical model and were found in good agreement. It is observed that at high stoichiometric ratios, the diffusion of SO2 from the gas bulk to the droplet interface is dominant for absorption and with decreasing stoichiometric ratio the absorption efficiency decreases. An increase in the temperature also causes a decrease in absorption efficiency. At the stoichiometric ratio (Na/S = 2), SO2 removal efficiency was found to be around 90%. (c) 2006 Elsevier B.V. All rights reserved.