Over the last years, the management of municipal solid waste (MSW) has been renovated and modernized. Timely treatment or storage of municipal waste does not, however, solve the problem of the threat MSW may pose for human life and environment. Therefore, projects of modern thermal plants for the processing of municipal solid waste, such as eco-incineration plants, have been launched on the market. It is not only possible to carry out the process of utilization of MSW, but also to obtain renewable energy. The result of MSW incineration is fly ash and bottom ash. In the fly ash composition, there are present chemical compounds such as silicon dioxide, magnesium oxide, aluminum oxide and calcium oxide. The carbonation process is a process in which calcium or magnesium oxide may react with carbon dioxide, forming carbonates. The mineral carbonation is possible with the use of high-calcium fly ash as one of the substrates of this chemical reaction. As a result, it produces carbonates which are not harmful to the environment as well as to humans. The idea of the experiment was to carry out the process of mineral carbonation of fly ash from the thermal treatment plant of municipal solid waste. The whole process was carried out at elevated pressure, and temperatures. After the experiment, several instrumental analyses were performed on the tested samples, such as XRD analysis, SEM scanning electron microscopy and IR infrared spectroscopy. The free calcium content was determined.