This study examines the effect of the chemical composition and origin on the performance of two calcitic and two dolomitic limestones from different sources in South Africa. The experiments were carried out in a fixed bed reactor maintained at 80 degrees C. The raw sorbent materials were calcined at 900 degrees C and the resulting quicklime hydrated to produce the relevant hydrates which were used in the tests. Results obtained show that the maximum temperature rise during the hydration of the samples varied from 5 to 65 degrees C depending on the chemical composition of the sorbent. Sorbents with higher temperature rise resulted in products with a more porous structure and a better performance in the sulphur capture. The maximum sorbent conversion in terms of mol of SO, per mol of sorbent varied from 0.0274 for dolomitic limestones to 0.1823 for the calcitic limestones. The presence of Fe2O3 in small quantities was observed to have a positive effect on the performance of the sorbent. (c) 2007 Elsevier Ltd. All rights reserved.