Volume changes for mixing the major sea salts: Equations valid to ionic strength 3.0 and temperature 95°C

Equations in the ion-interaction (Pitzer) system are derived for the volume change on mixing any combination of the sea salts NaCl, Na₂SO₄, MgSO₄, MgCl₂ at constant ionic strenth. For these mixings of different charge types, the equations include complex differences of pure electrolyte terms. Recently measured data for each of the pure electrolytes provide these pure electrolyte terms. Other recent measurements on the volume change on mixing are compared with values calculated from the equations. At 25°C there is no need to introduce the mixing terms based on differences in the interactions of ions of the same sign. At other temperatures, the agreement without the mixing terms is good, but significant improvement is obtained by inclusion of the binary mixing terms Cl,SO ₄ ^v and _Na,Mg ^v . The equations and parameters can then predict the volumetric properties of any mixed solution of these salts over the range 0–100°C and to at least 3 mol-kg^–1 ionic strength.