Extraction characteristics and radiation stability of the CHALMEX process for separation of Am(III) and Eu(III) at different temperatures

[Display omitted] •The understanding of the CHALMEX process was significantly improved.•Mass transfer was identified as the rate-controlling process of Am(III) extraction.•Free enthalpy and entropy for Am(III) and Eu(III) extraction were determined.•The main pathways of the CyMe4-BTBP transformation under irradiation were proposed.•Some CyMe4-BTBP degradation products are efficient Am(III)/Eu(III) extractants. The behavior of the CHALMEX system comprising CyMe4-BTBP extractant in 30% tri-n-butyl phosphate and 70% phenyl trifluoromethyl sulfone diluents was characterized. The kinetic model based on mass transfer as the rate-controlling process was found to best describe the kinetics of Am(III) and Eu(III) extraction; the overall mass–transfer coefficients were determined. The dependence of distribution coefficients on temperature allowed change in free enthalpy and entropy of the system to be calculated. An investigation into the extraction properties of various CHALMEX systems combinations after irradiation with accelerated electrons up to an absorbed dose of 500 kGy at different temperatures up to 45 °C was carried out together with the characterisation of radiolytic products and their quantification using LC-MS and 1H NMR. The results obtained suggest that some of the radiolytic degradation products/adducts are efficient Am(III)/Eu(III) extractants, extracting Am and Eu by the ion-exchange mechanism. Adducts formed by hydroxylation or transfer of the CF3 moiety to the CyMe4-BTBP molecule are formed under irradiation together with products formed by elimination of a triazine ring or a cleavage of triazine ring(s). The results obtained now allow for a scheme of the main pathways of the CyMe4-BTBP molecule transformation under irradiation to be proposed.