Pyrohydrolysis of SmF3 in moist air

• Published in: Journal of fluorine chemistry 2017-01, Vol.193, p.106-112
• Main Authors: Peng, Jia, Zheng, Xiaobei, Qiu, Tingting, Gao, Size, Liu, Yuxia, Zhang, Lan
• Format: Article
• Language: English
• Subjects: Kinetics; Pyrohydrolysis; Reaction mechanism; SmF3; Thermogravimetry
• ISSN: 0022-1139; 1873-3328
• DOI: 10.1016/j.jfluchem.2016.11.011

There were two stages of pyrohydrolysis process of SmF3 correspond to the conversion of SmF3 into SmOF and SmOF into Sm2O3. The rate-determining step of pyrohydrolysis was the surface reaction control, and the shrinking core model was applied to describe the mechanism. [Display omitted] •Pyrohydrolysis of SmF3 obeys the phase boundary rate law.•Sm2O3 was generated on the surface layer with parceled SmOF kernel particles.•The shrinking core model can be used to describe the mechanism of SmF3 pyrohydrolysis.•Rate-determining step of pyrohydrolysis was the surface reaction control. In order to prove the feasibility of pyrohydrolysis method of fluorides in TMSR spent fuel reprocessing, pyrohydrolysis behavior and reaction mechanism of neutron poison represented by SmF3 in moist air, have been studied by means of thermogravimetric analysis (TG). Then, reaction products in solid state were characterized by means of XRD and SEM. The results indicated that SmF3 began to hydrolyze in 773K. Two definite breaks on TG curves were correlated to the conversions of SmF3 into SmOF and SmOF into Sm2O3, respectively. Through the simulation calculation, we found that the two stages of the reaction can both meet the second-order reaction kinetics, and their corresponding activation energies are 60.2 and 31.2kJ/mol, respectively. From the results of dynamics simulation, the rate equation obeyed the phase boundary rate law, which was expressed by [1 − (1−x) 1/3]=kt. Further studies indicated that the rate-determining step was the surface reaction control, and the shrinking core model was applied to describe the mechanism. These results showed that pyrohydrolysis method of fluorides could be used for fuel reprocessing due to its unique reaction mechanism.