## Abstract

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 [O_{2}]^{0}/[O_{2}] = lnγ(O_{2}) = k_{s}m The ratio of the solubility of oxygen (μmol kg^{-1}) in water [O_{2}]^{0} and solution [O_{2}] is equal to the activity coefficient (γ) at a given molality (m), and k_{s} is the salting coefficient. In this paper, measurements of the solubility of oxygen in the major sea salts (NaCl, MgCl_{2}, Na_{2}SO_{4}, and MgSO_{4}) from dilute solutions to saturation at 25°C are examined. Measurements were also made on mixtures of the major sea salts (NaCl + Na_{2}SO_{4}, NaCl + MgCl_{2}, Na_{2}SO_{4} + MgSO_{4}, MgCl_{2} + MgSO_{4}, NaCl + MgSO_{4} and Na_{2}SO_{4} + MgCl_{2}). The solubilities [O_{2}] have been fitted to equations of the form: ln[O_{2}] = A + Bm + Cm^{2} where A, B, and C are empirical constants. The salting coefficient k_{S} 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 (m_{T}). The values of k_{S} for the mixtures can be estimated from the endmembers by: k_{S}(NaCl + MgSO_{4}) = N_{NaCl}k_{S}(NaCl) + N_{MgSO4} k_{S}(MgSO_{4}) where N_{i} 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 k_{S} of the salts into ionic components [k_{S}(NaCl) = k_{S}(Na^{+}) + k_{S}(Cl^{-})] yields different values for k_{S}(SO^{2-}_{4}) from Na_{2}SO_{4} and MgSO_{4} solutions. This is related to different interactions of SO^{2-}_{4} with Na^{+} and Mg^{2+} ions. These interactions are accounted for using the Pitzer equations: lnγ_{02} = 2∑_{c}λ_{02c}m_{c} + 2∑_{a}λ_{02a}m_{a} + 2∑_{N}λ_{02N}m_{N} + Elsevier Science Ltd.

Original language | English (US) |
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Pages (from-to) | 2349-2359 |

Number of pages | 11 |

Journal | Geochimica et Cosmochimica Acta |

Volume | 66 |

Issue number | 13 |

DOIs | |

State | Published - Aug 12 2002 |

## ASJC Scopus subject areas

- Geochemistry and Petrology