Abstract:The state of uranium is an important condition that determines its migration ability in water. A data set from lab leaching experiments under different CO2 and O2 pressures were synthetically studied in geochemical model software PHREEQC, aiming to decipher influencing factors of Eh-pH field in uranium leaching system. The results show that, in CO2+O2 leaching uranium system, uranyl carbonate complex is the main form of uranium in water, pH value of water affects the critical pH value of dominant domain of uranyl carbonate complex, and HCO3- concentration is the main controlling factor for change of uranium redox critical potential. It indicates that CO2 is the fundamental factor for these changes.