Abstract
A study was made to examine the behavior of fluoride in the process of concentrating sea water by ion exchange membrane method. The Alizarin complexon method was employed for carrying out an analysis of fluoride. However, it was necessary, especially in the analysis of concentrated solution, to add some sodium chloride to samples for avoiding errors to be derived from a change in the concentration of sodium chloride.
The permselectivities of fluoride to chloride TFCl in sea water were as small as about 0.1, representing a half or one-third of those of sodium chloride solution. The differential permselectivity TFCl in sea water was constant (about 0.17) in the region of less than 60% in degree of desalting for chloride. As for the small apparent permeability of fluoride in sea water, it seemed to be reasonable to consider that fluoride formed complex ion with a cation or cations in sea water. As the result of our examination on the effects of cations in sea water upon the permeability of fluoride, effects of magnesium were found to be great, but fluoride was found to be never concentrated as cations. The form of the complex ion was approximately MgF+, and the constant of its formation was about 101·8 at 20-40°C. Therefore, our conclusion was that most of fluoride contained in sea water existed in the form of MgF+ and seemed to hardly permeate through the cation exchange membrane in the form of MgF+, but F- which was in equilibrium with the MgF+ permeated through the anion exchange membrane.
