Light-scattering characteristics of hydrated ions in dilute solutions of major sea salts

The major ions in seawater include Na+, Mg2+, Cl−, Ca2+, and K+, altogether accounting for >96% of the total mass of sea salts. The radii of ions in solution depend on the number of the solvent molecules in their solvation shells, and so would have an influence on the light-scattering of the aqueous solution. Taking in to account density fluctuation theory of pure water and Rayleigh scattering of hydrated ions, a theoretical model was developed estimating the light-scattering characteristics of the dilute ionic aqueous solution. The results show that there is a decreasing contribution due to density fluctuation, in the same salinity of solution, the most contribution to scattering due to density fluctuation is CaCl2 solution and MgCl2 > KCl > NaCl. There is an increasing contribution due to hydrated ions for the light scattering. For each kind of hydrated ion, the contribution is Cl− > Mg2+ > K+ > Ca2+ > Na+, and for each kind of solution, the contribution is MgCl2 > CaCl2 > NaCl > KCl. Comparing the two contribution for the light scattering in one solution, we can get the latter effect dominating.