Using a K2CO3/piperazine (PZ) mixture as a typical phase-change absorbent has promising applicability for carbon dioxide (CO2) capture in coal-fired power plants that would contribute to low energy consumption for solvent regeneration. In this study, the reaction rate of CO2 with a concentrated K2CO3/PZ mixture was measured in a wetted-wall column. At a CO2 loading close to saturation absorption, correlative physical parameters were calculated. The effects of operating conditions, including gas flow rate, slurry flow rate, PZ concentration, CO2 loading, K2CO3 mass fraction, and temperature, on the absorption rate of CO2 were investigated. The results showed that the absorption rate was sensitive to the effects of the gas flow rate and CO2 loading. The PZ concentration and K2CO3 mass fraction also substantially influenced the CO2 absorption rate. However, minor changes in the CO2 absorption rate were observed when the slurry flow rate and temperature were increased. On the basis of a pseudo-first-order model, the absorption rate determined in this study was found to be controlled by mass transfer in both the gas film and the liquid film. The results can serve as a useful reference for designing CO2 removal systems using K2CO3/PZ mixtures.