Oxygen solubility modelling in water and brines


Oxygen solubility modelling in water and brines

Bok, F.; Moog, Helge C.

Dissolved molecular oxygen influences the chemistry of various redox reactions in the aqueous solution e.g. corrosion processes, microbial activity or the immobilisation of radionuclides. In the presence of dissolved oxygen, the poorly soluble (hydro)oxides of reduced actinides, e.g. U(OH)₄(am), PuO₂(am/cr) get oxidized and these elements become more soluble in water. Furthermore, the activity of dissolved oxygen is used as redox parameter in common geochemical codes (i.e. Geochemist’s Workbench®). Thus, the correct prediction of the O₂ solubility in water and saline solutions is necessary for the correct modelling of redox processes in water and in brines especially.
For reasons of consistency, the few existing sets of O₂-ion interaction coefficients for the Pitzer model cannot be used in combination with the THEREDA Pitzer model for the oceanic salt system and would result in wrong gas solubility calculation’s results. Therefore, a new and consistent set of solubility parameters was deduced using published O₂ solubility data in water and binary and ternary salt solutions from ~100 literature references.
First a critical review of the published data on oxygen solubility in water and salt solutions has been performed. Using these data, the temperature function of the O₂ Henry’s constant could be obtained valid for the temperature range 273–618 K. Then a consistent set of Pitzer interaction coefficients including its temperature function’s parameters was deduced for the calculation of the amount of dissolved oxygen in aqueous solution and brines. All parameters have been determined using the geochemical speciation software PHREEQC coupled with the parameter estimation software UCODE-2005.
A self-consistent set of Pitzer interaction coefficients for the description of oxygen solubility in binary and some ternary salt solutions could be obtained for the system Na⁺, K⁺, H⁺, Ca²⁺, Mg²⁺ / Cl⁻, SO₄²⁻, CO₃²⁻, PO₄³⁻, OH⁻ - H₂O(l). For the chloride and the sulphate subsystems, temperature function parameters could be obtained to describe the temperature dependency of the O₂ solubility in these salt solutions.

Keywords: Saline solutions; Redox; Oxygen; Pitzer; Solubility

  • Lecture (Conference)
    17 International Symposium on Solubility Phenomena and Related Equilibrium Processes (ISSP17), 24.-29.07.2016, Geneva, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-23599
Publ.-Id: 23599