Oxygen solubility modeling in aqueous solutions

Oxygen dissolved in the aqueous phase (O₂)_aq is an important oxidant in many industrial processes, ranging from pressure leaching and heap leaching of metals from minerals to the bleaching of wood fibers in the pulp and paper industry. Frequently, (O ₂)_aq is a prime agent promoting corrosion of metals in aqueous systems. This study presents a general solubility model for estimating oxygen solubility in aqueous inorganic solutions over a wide range of conditions. These include changes in oxygen partial pressure P(O₂) (atm), variations in the process temperature T (K), and changing concentrations C_t of dissociated inorganic solute I. The model is based on a thermodynamic analysis showing that the concentration c_aq of (O₂)_aq in pure water is dependent upon P(O₂) and T via an equation of the form c_aq=P(O₂)f(T), where f(T) is a T-dependent function related to the chemical potential, entropy, and partial molar heat capacity of the gaseous oxygen (O₂)_g and dissolved (O₂)_aq species. In the presence of a single I, this equation is modified by a φ-factor such that the new oxygen solubility, (c_aq)_I, becomes (c_aq)_I=φc_aq=φP(O₂ )f(T), where φ is an I-dependent function of C_I. Inorganic solutes of similar stoichiometry, composed of a common anion and having cations from the same group in the Periodic Table, tend to exhibit a similar φ-factor and (c_aq)_I value, provided all concentrations, c_aq, (c_aq)_I, and C_I, are reported in molal (m) units (mol/kg H₂O). Methods for incorporating the effect of multiple I on φ are presented and discussed