Separation of seawater by Soret diffusion

Abstract

Samples of artificial seawater were separated in a Clusius-Dickel (thermogravitational) column at temperatures from 5 to 40°C at atmospheric pressure. The ions represented were sodium, magnesium, potassium, calcium, chloride and sulfate. The samples were analyzed by atomic absorption for the positive ions, and by titration for the negative ions. From the separations, ionic Soret coefficients were calculated. A multi-component effect was found, that is, the ionic coefficients were not the same as those we measured previously for the same ions in binary salts, but, except for the sulfate ions, the Soret coefficients were similar to those in binary salts. Because the difference between binary salts and this complex solution affects the coefficients only moderately, the results should be applicable to a wide range of natural waters. In the interfaces above the Red Sea brines, Soret diffusion opposes Fickian diffusion, tending to keep the sulfate in the normal Red Sea waters from penetrating to the sulfate-depleted brines.