Thermodynamic Modeling of Aqueous Electrolyte Systems: Current Status

Abstract

The current status of thermodynamic modeling in aqueous chemistry is reviewed. A number of recent developments hold considerable promise, but these need to be weighed against ongoing difficulties with existing theoretical modeling frameworks. Some key issues are identified and discussed. These include long-standing difficulties in choosing the right program code, in comparing alternatives objectively, in implementing models as published, and in wasting effort on numerous proposed “modifications” and/or “improvements”. There needs to be greater awareness of the major limitations that such assorted variations in modeling functions imply for practical thermodynamic modeling purposes. They typically lack proper substantiation, fail to distinguish between cause and effect, and are presented in ways that all-too-often cannot be falsified. Numerical correlations in particular permit overoptimistic assertions based only on “satisfactory” fits, neglecting the dictum that regression analyses can be used to discredit hypotheses but not to prove them. The risks of “model tuning” should always be acknowledged and minimized. Recognition of the uncertainties in data that have not been confirmed by independent measurement needs to be redoubled. Modeling frameworks incapable of explicit trace activity coefficient prediction should no longer be regarded as credible. The current modeling paradigm evidently has to be reassessed, hopefully to find better ways forward, including new protocols which command sufficient support to warrant IUPAC endorsement.

Thermodynamics of primitive model electrolytes in the symmetric and modified Poisson-Boltzmann theories. A comparative study with Monte Carlo simulations

“…Designing many of the important industrial chemical processes involving aqueous electrolytes requires an understanding of the thermodynamics of these systems. Ion-ion or ion-surface charge interactions of electrolyte solutions in water are fundamental processes also in areas such as biology and physical chemistry (see for example, references [1][2][3][4][5][6][7][8][9][10]). These interactions relate to the activity of water and the individual activities of the ions in solution.…”

Salt Solubilities in Aqueous Solutions of NaNO3, NaNO2, NaCl, and NaOH: A Hofmeister-like Series for Understanding Alkaline Nuclear Waste

“…Despite extensive investigation for more than 100 years, salt solubility in multicomponent aqueous electrolyte solutions are still not well described theoretically except in the most dilute solutions. 1 The cause of this difficulty is in part because of what are called “specific interactions”, 2 which are interactions between different constituents in the solution. All ions create an electric field in solution because they are charged.…”

“… 3 − 5 Unfortunately, the current models must be parameterized with the experimental data for concentrated solutions, which can require substantial experimentation to capture all of the specific interactions between all ions in systems with many components. 1 While it is certainly possible to determine a large number of interaction parameters experimentally, it is cost prohibitive in many cases. Voigt emphasized this point with seawater.…”

Activity Coefficients of Concentrated Salt Solutions: A Monte Carlo Investigation

“…The single ion activity is otherwise difficult to calculate from theory [54]. Moreover, simulations are less approximate than theories and usually theoretical results are first evaluated against computer simulations before comparing them with experimental data [55]. We shall start our exploration of this interesting issue by simulating the mean ionic activity and osmotic coefficients of HCl at 25 °C.…”