The characteristics of the gas-liquid interfacial area (a) and the true liquid-side (k(L)) and volumetric (k(L)a) mass transfer coefficients were investigated in the riser of a three-phase circulating fluidized bed (TPCFB). The values of k(L)a and a were determined from the simultaneous physical desorption of O-2 and chemical absorption of CO2 into the liquid phase. The effects of the gas (U-G: 0.02-0.08 m/s) and liquid (U-L: 0.24-0.32 m/s) velocities, particle size (d(P): 0.5-3.0 x 10(-3) m) and solid circulation rate (G(S): 2.0-8.0 kg/m(2)s) on the values of k(L)a, a and k(L) were examined. The values of k(L)a and a increased with increasing gas velocity, particle size and solid circulation rate but increased only slightly with increasing liquid velocity in the riser. The true liquid-side mass transfer coefficient increased with increasing gas and liquid velocities, particle size and solid circulation rate. The values of k(L)a, a and k(L) were well-correlated in terms of the operating variables such as gas and liquid velocities, particle size and solid circulation rate. (C) 2013 Elsevier Ltd. All rights reserved.