5 pages.-- Final full-text version of the paper available at: http://dx.doi.org/10.1021/es0351589.The optimization of parameters of synthesis of belite cement clinker from coal fly ash of high Ca content is presented in this paper. The synthesis process is based on the hydrothermal-calcination-route of the fly ash without extra additions. The hydrothermal treatment was carried out in demineralized water and a 1 M NaOH solution for 4h at the temperatures of 100 °C, 150 °C, and 200 °C. The precursors obtained during the hydrothermal treatment were heated at temperatures of 700 °C, 800 °C, 900 °C, and 1000 °C. The changes of fly ash composition after the different treatments were characterized by X-ray diffraction (XRD), FT infrared (FTIR) spectroscopy, surface area (BETN2), and thermal analyses. From the results obtained we concluded that the optimum temperature of the hydrothermal treatment was 200 °C, and the optimum temperature for obtaining the belite cement clinker was 800 °C.The authors gratefully acknowledge the financial support by the Minister of Science and Technology (Project no. MAT 2002-04023-CO1-CO2-CO3) and the Thermal Station of Cercs (Catalonia) for the fly ash supplied.Peer reviewed