A chemical model for the major electrolyte component of seawater based on the Brønsted-Guggenheim hypothesis

The Brønsted-Guggenheim hypothesis of specific ionic interaction is used to develop a chemical model for the major electrolyte components in seawater (Na⁺---K⁺---Mg²⁺---Ca²⁺---Cl⁻---SO₄²⁻ at 25°C and 1 atm total pressure. The model is shown to be in essential agreement with models based on the Bjerrum ion-association hypothesis (e.g., Garrels and Thompson, 1962), with calculations based on the ionic hydration and cluster expansion theories of electrolyte solutions, and with available experimental evidence.The Brønsted-Guggenheim model is computationally simpler than the currently accepted Bjerrum model and results directly in the conventional total single-ion activity coefficients that are most commonly required for calculations in seawater equilibria. The simple form of the equations should enable the model to be extended quite readily to cover a wide range of temperature, pressure and solution composition. However, applications are at present restricted by the availability of the appropriate interaction coefficients.