Development of accurate chemical thermodynamic database for geochemical storage of nuclear waste. Part II: Models for predicting solution properties and solid-liquid equilibrium in binary nitrate systems

 The main purpose of this study is to develop new thermodynamic models for solution behavior and solid-liquid equilibrium in 10 nitrate binary systems of the type 2-1 (Mg(NO[sub.3])[sub.2]-H[sub.2]O, Ca(NO[sub.3])[sub.2]-H[sub.2]O, Ba(NO[sub.3])[sub.2]-H[sub.2]O, Sr(NO[sub.3])[sub.2]-H[sub.2]O, and UO[sub.2](NO[sub.3])[sub.2]-H[sub.2]O), 3-1 (Cr(NO[sub.3])[sub.3]-H[sub.2]O, Al(NO[sub.3])[sub.3]-H[sub.2]O, La(NO[sub.3])[sub.3]-H[sub.2]O, Lu(NO[sub.3])[sub.3]-H[sub.2]O), and 4-1 (Th(NO[sub.3])[sub.4]-H[sub.2]O) from low to very high concentration at 25 °C. To construct models, we used different versions of standard molality-based Pitzer approach. To parameterize models, we used all available raw experimental osmotic coefficients data ([PHI]) for whole concentration range of solutions, and up to supersaturation zone. The predictions of developed models are in excellent agreement with [PHI]-data, and with recommendations on activity coefficients ([GAMMA][sub.±]) in binary solutions from low to very high concentration. The Deliquescence Relative Humidity (DRH), and thermodynamic solubility product (as ln K°[sub.sp]) of 12 nitrate solid phases, precipitating from saturated binary solutions have been calculated. The concentration-independent models for nitrate systems described in this study are of high importance for development of strategies and programs for nuclear waste geochemical storage. Keywords: Nuclear waste sequestration, Chemical modelling, Pitzer approach, DRH and K°[sub.sp] of Mg(NO[sub.3])[sub.2].6H[sub.2]O(s), Ca(NO[sub.3])[sub.2].4H[sub.2]O(s), Ca(NO[sub.3])[sub.2].3H[sub.2]O(s), Ba(NO[sub.3])[sub.2](s), Sr(NO[sub.3])[sub.2](s), UO[sub.2](NO[sub.3])[sub.2].6H[sub.2]O(s), Al(NO[sub.3])[sub.3].9H[sub.2]O(s), Cr(NO[sub.3])[sub.3](s), La(NO[sub.3])[sub.3].6H[sub.2]O (s), La(NO[sub.3])[sub.3](s), Lu(NO[sub.3])[sub.3].5H[sub.2]O(s) and Th(NO[sub.3])[sub.4].6H[sub.2]O(s)