The mass-transfer rate and reaction kinetics play important roles in the removal of acidity gases and in gas-liquid reactive crystallization processes. in order to determine the absorption rate, a multiple-tube plug-flow model was adopted. For sake of gaining a better understanding of the effects of process variables on the absorption of acidity gas, i.e., carbon dioxide, into an alkaline solution containing fine barium carbonate crystals, a continuous bubble-column scrubber under a pH-stat condition was used. Assuming a two-film mechanism with fast second order reaction under the operating conditions applied in this work, the masstransfer coefficients could be obtained successfully. The effects of solid loading, the pH of the solution, gas concentration, gas-flow rate, and liquid-flow rate on the absorption rate and volumetric mass-transfer coefficient of carbon dioxide were investigated. Correlations of volumetric mass-transfer coefficients with process variables are investigated here and the gasliquid interfacial area and local mass-transfer coefficient are discussed to provide insight into the mass-transfer mechanism.