The paper gives high-temperature isothermal data on sulfur dioxide (SO2) capture, obtained as a function of temperature, SO2 partial pressure, and Ca/S molar ratio for a pulverized dolomite (34 micrometer mean size) and a high-purity calcite (11 micrometer mean size). The experimental results indicated that sulfur capture increases approximately linearly with increasing Ca/S ratio and is relatively insensitive to SO2 partial pressure at the conditions tested. Reaction zone temperature was found to critically influence the overall effectiveness of sulfur capture by sorbent injection; as the local temperature increases, the rates of heterogeneous chemical reaction and diffusion increase, but these are ultimately compensated for by a decrease in initial sorbent surface area due to desurfacing during flash calcination. The experimental results were compared with theoretical predictions using a combined diffusion/heterogeneous chemical reaction model which was developed based on a grain formulation. Initial analysis of various fundamental kinetic studies suggested that the intrinsic chemistry was first order in calcium sites and zero order in SO2 partial pressure. Model predictions showed good qualitative and quantitative agreement with experimental data. Analysis of temperature profiles from full-scale utility boilers suggests a strong dependency on quench rate in the sulfation zone.