Thermodynamic database for silicate species in aqueous sodium salt solution at 298°K and 1 atm

The database provides effective equilibrium constants of oligomerization and deprotonation reactions of (poly-)silicate aqueous species and their variation with ionic strength, 0 < I < 2 M to be used for classical geochemical modeling (e.g. PHREEQC, GEMS etc). The effective equilibrium constants were obtained from averaging out the results of a microscopic model for silicate speciation, based on the primitive model, parametrized against independent experimental data and solved with Monte Carlo simulations using the grand canonical titration scheme developed by Labbez and Jönsson1. The variation of the effective constant with the ionic strength obeys a Debye-Hückel-like equation of the form pK_eff(I) = pK_eff(0) + A·sqrt(I)/(1 + sqrt(I)) + B·I + C·I² + D·I³ The domain of validity of the current version of the database (v1) is limited to sodium salt solutions with 0 < I < 2 M and at 0 < pH < 12. Future versions of the database will include silicate species with higher degree of polymerization (currently, DP = 1–4) as well as the complexation constant with calcium ion. [1] C. Labbez, B. Jönsson, A New Monte Carlo Method for the Titration of Molecules and Minerals, Lect. Note Comp. Sci. 4699 (2007) 66–72. Contents: README.md: overview and usage instructions. pkeff_generator.py: small python program to generate the list of reactions and associated log K to be used in PHREEQC at a given ionic strength parameter_file.dat: data file providing the parameters of the Debye-Huckel-like equation for the effective equilibrium constants of deprotonation reactions oligomerization_constant.dat: data file providing the equilibrium constant for the oligomerization reactions logK_I_0.6.dat: example file for PHREEQC reaction block with all silicate deprotonation and oligomerization log K values at I = 0.6 M, computed from the python script.