Thermodynamic study of uranium in the process of coal thermal utilization

Uranium is a kind of radionuclide and also an important strategic resource. In some areas of China, the content of U in coal is extremely enriched. After high temperature transformation, U in coal can be enriched in solid products, which may cause radioactivity risk. In order to control the release of U and transform U in coal products into resource, it is necessary to investigate the migration law of uranium during thermal utilization of coal. Based on the thermodynamic equilibrium principle, the morphology distribution of uranium was calculated and analyzed in the processes of pyrolysis, gasification and combustion of Ganhe coal, Xiaolongtan coal and Shengli coal. Also the influence of calcium based additives on U migration was analyzed to provide theoretical guidance for subsequent experimental studies. The results show that uranium has different forms in pyrolysis, gasification and combustion processes; UO₃(g) is the only gas phase product produced under different working conditions, and higher temperature, lower pressure and stronger oxidation environment can increase the formation amount of UO₃(g); volatilization of uranium is significantly week when uranium is fixed to form calcium uranate. Especially, the amount of calcium uranate in Ganhe coal during combustion is increased obviously after the use of calcium based additives and the effect of CaO is the most significant.