The solubility of gases and other non-electrolytes in electrolyte solutions are normally examined using the Setschenow (1899) equation, which for oxygen is given by: ln [O2]0/[O2] = lnγ(O2) = ksm The ratio of the solubility of oxygen (μmol kg-1) in water [O2]0 and solution [O2] is equal to the activity coefficient (γ) at a given molality (m), and ks is the salting coefficient. In this paper, measurements of the solubility of oxygen in the major sea salts (NaCl, MgCl2, Na2SO4, and MgSO4) from dilute solutions to saturation at 25°C are examined. Measurements were also made on mixtures of the major sea salts (NaCl + Na2SO4, NaCl + MgCl2, Na2SO4 + MgSO4, MgCl2 + MgSO4, NaCl + MgSO4 and Na2SO4 + MgCl2). The solubilities [O2] have been fitted to equations of the form: ln[O2] = A + Bm + Cm2 where A, B, and C are empirical constants. The salting coefficient kS is equal to -(B + C m), and the value of (∂lnγ/∂m)m=o = -B. The mixtures were also fitted to similar equations, where m is replaced by the total molality (mT). The values of kS for the mixtures can be estimated from the endmembers by: kS(NaCl + MgSO4) = NNaClkS(NaCl) + NMgSO4 kS(MgSO4) where Ni is the mole fraction of the salt (i). This equation predicts solubilities for the mixtures that are in reasonable agreement with the measured values (±20 μmol kg-1). The division of the values of kS of the salts into ionic components [kS(NaCl) = kS(Na+) + kS(Cl-)] yields different values for kS(SO2-4) from Na2SO4 and MgSO4 solutions. This is related to different interactions of SO2-4 with Na+ and Mg2+ ions. These interactions are accounted for using the Pitzer equations: lnγ02 = 2∑cλ02cmc + 2∑aλ02ama + 2∑Nλ02NmN + Elsevier Science Ltd.
ASJC Scopus subject areas
- Geochemistry and Petrology