Limited utilization possibilities of high–calcium fly ashes (HCFA) are a serious issue not only in Europe, but also worldwide. The properties of such waste from coal-fired power plants could be conveniently treated in order to make their compositions compliant with national regulations and allow their use in a variety of industrial applications. This work reports on an investigation of mineral carbonation of HCFA from Greece, Poland and Spain with total CaO contents between 10 and 15 wt.%. Two types of experiments, batch and continuous flow, with and without the addition of water vapor, were performed. Best carbonation efficiency obtained was 47% of the bulk CaO content. The free lime content of the samples was found to be the controlling factor. After treatment, the amount of free lime was reduced to values suitable for their utilization as supplementary cementitious materials. The addition of water to the system played also an important role in the progress of the carbonation reactions. Our results strongly suggest that a carbonation treatment of HCFA could contribute to the circular economy of such waste materials and potentially increase their utilization in the construction industry, as well as make a significant contribution to lowering of the CO2 emissions in coal-burning industrial facilities.

Peer Reviewed