Potassium-doped lithium zirconate (Li2ZrO3) sorbents with similar crystallite but different aggregate sizes were prepared by a solid-state reaction method from mixtures of Li2CO3, K2CO3, and ZrO2 of different particle sizes. Carbon dioxide sorption rate on the prepared Li2ZrO3 sorbents increases with decreasing sorbent aggregate size. It is the size of the aggregate, not the crystallite, of Li2ZrO3 that controls the sorption rate. Temperature effect on CO2 sorption is complex, depending on both kinetic and thermodynamic factors. A mathematical model based on the double-shell sorption mechanism was established for CO2 sorption kinetics and it can fit experimental data quite well. Above 500degreesC, the rate-limiting step Of CO2 sorption is the diffusion of oxygen ions through the ZrO2 shell formed during the carbonation reaction. Oxygen ion conductivities in the ZrO2 shell were obtained by regression of the experimental CO2 uptake curves with the model and are consistent with the literature data. (C) 2003 Elsevier Ltd. All rights reserved.