Extended Pitzer activity model for the system M(III) − Na+ − Mg2+ − Ca2+ − H+ − Cl- − NO3- − OH- − H2O(l) (M = Am, Cm, Nd) at 25°C

The Thermodynamic Reference Database (THEREDA, www.thereda.de) selected thermodynamic data for Am(III), Cm(III) and Nd(III) in the previous releases No. 2 (2011) Am(III), Cm(III), Nd(III) – Na+, Ca2+, Mg2+, Cl-, OH- – H2O(l) () and No. 8 (2013): Am(III), Cm(III) – Na+ – Cl-, SO42-, CO32- – H2O(l). The present work builds on these releases by extending the Pitzer activity model to include interactions with NO3-. The extension of the system by nitrate is consistent with the latest NEA-TDB selection and is based on available solubility studies in dilute to concentrated saline systems. The extended model includes the species M3+, MOH2+, M(OH)2+, M(OH)3(aq), M(OH)4-, MCl2+, MCl2+, MNO32+, M(NO3)2+, Ca[M(OH)3]2+, Ca2[M(OH)4]3+, Ca3[M(OH)6]3+, Mg[MNO3OH]3+ and Mg[MNO3(OH)2]2+ among which the four NO3- containing species are new in THEREDA. The updated model accurately describes solubility data for M = Am, Cm and Nd in dilute to concentrated pure chloride, pure nitrate and mixed Cl-/NO3- systems containing Na+, Mg2+ and Ca2+.