Effect of the product layer on the kinetics of the CO₂‐lime reaction

The kinetics of reaction between CO 2 and lime is investigated in the range of 673 to 998 K with a view to examining the effects of product layer deposition and variations in the limestone calcination atmosphere. The reaction is initially rapid and chemically controlled and goes through a sudden transition to a much slower regime controlled by diffusion in the product CaCO 3 layer. The magnitude of the estimated product layer diffusivity is in the range of 10 −18 to 10 −21 m 2 /s, the corresponding activation energy is 88.9 ± 3.7 kJ/mol below 688 K and 179.2 ± 7.0 kJ/mol above that temperature, suggestive of solid state diffusion. Plausible mechanisms are discussed.