This work explores the reaction mechanisms for the sonochemical-enhanced carbonation of fluidized bed combustion (FBC) ash. Ashes from Nova Scotia Power's 165 MWe circulating fluidized bed combustor (CFBC) as well as synthetic ash prepared directly from limestone have been used. Acetone tests were carried out using pure acetone as well as acetone/water mixtures (4:1 ratio). Tests with acetone demonstrated that, without previous hydration of the ash, significant carbonation is not achieved. Experiments were also conducted to determine the role of hydration temperature on the carbonation of FBC ash. X-ray diffraction (XRD) analysis of synthetic ash after sonication has also been carried out. Analysis of the data obtained revealed that the process is well described by a series reaction mechanism. Initial hydration temperature does not appear to significantly impact the carbonation of FBC ash. Synthetic ash does not behave like FBC ash due apparently to its extreme susceptibility to the size reduction capability of ultrasonics. (c) 2007 Elsevier Ltd. All rights reserved.