Sulfur dioxide pollutant was treated in the laboratory with hydrated lime particles having a mean diameter of 9.1 mum in a continuously operating binary fluidized bed reactor also containing inert sand particles with sizes varying from 500 to 590 mum. The influence of temperature (500, 600, 700 and 800 degreesC) on the reaction medium, of the superficial velocity of the gas (0.8, 1.0 and 1.2 m/s), and of the Ca/S molar ratio (1, 2 and 3) on the SO2 removal efficiency were investigated for an inflow gas concentration of 1000ppm and an initially static bed height of 10.0cm. The pollutant removal efficiency proved to depend on the temperature and the velocity of the gaseous flow and was strongly influenced by the Ca/S molar ratio. The maximum efficiency of 97.7% was achieved at a temperature of 700 degreesC, a Ca/S ratio of 3 and a velocity of 0.8 m/s. The lime particles' mean residence time was determined by an indirect method, which consisted of integrating the gas concentration curves normalized with respect to time. Based on a calculation of the critical transition velocities, it was concluded that the reactor operated in a bubbling regime under each condition investigated here. (C) 2004 Elsevier B.V. All rights reserved.