1977 Volume 30 Issue 5-6 Pages 261-270
In Japan, common salt is made by concentrating sea water by electrodialysis method and evaporating the concentrated sea water (ionic brine) in vacuum pans. As its characteristic, ionic brine is composed of chloride solution containing a negligible amount of SO42-. Therefore, the treatment of ionic brine such as its evaporation and so forth can be graphically calculated on the diagrams of the five component system; Na+, K+, Mg2+, Ca2+Cl--H2O.
In the previous paper, the author reported the method of graphical calculation for the evaporation of four kinds of ionic brines at three different temperatures by using the Janecke type triangular coordinated phase diagrams of the five component system saturated with NaCl, and concluded that the best NaCl yield could be obtained by evaporation to the point of KC1 saturation.
In this paper, the author tried to get some usefull applications to the salt manufacturing industry in our country.
(1) At first, the graphical calculations were made for the evaporation of four kinds of ionic brines (Table-1), at eight different temperatures, namely 0°C, 25°C, 35°C, 45°C, 50°C, 70°C, 75°C and 110°C (Fig.-1) to the saturation point of KCl. From the calculations, it was found that the NaCl yields brines of depended solely on the temperature of evaporation, and not on the brine composition. The higher temperatures gave better NaCl yields. The rate of evaporations also depended on the temperatures. In this case, however, the compositions of brines seemed to have some effects (Fig.-2).
(2) The NaCl yield y was shown by the following empirical formura:yt=85.4+6.3log t(Fig.-3).
(3) In the salt making procedure, the temperature of separating salt crystals by centrifuging salt slurry is very important. Because the mother liquor (or bittern) needs to have been just saturated with KC1. Therefore, a lower temperature of centrifuging gave a lower NaCI yield, and a smaller rate of evaporation.
(4) Then, the ratios (NaCl obtained/H2O evaporated) were calculated. These ratios depended solely on the compositions of brines, and not on the temperatures. Moreover, the ratios were nearly equal to the ratios of NaCl/H2O in the compositions of brines. The ratio means the amount of NaCl obtainable by the evaporation of a unit amount of water. In another word, it means the energy efficiency of evaporation.
(5) From the graphical calculation, it was found out that the ratios NaCl/H2O (y) could be calculated by the following empirical equation from NaCl concentrations in brines (x):y=-0.014+0.00115x (Fig.-5).
(6) To show some examples, monthly values of NaCl/H2O ratios of ionic brines in ten working electrodyalitic factories were shown in the graph (Fig.-6).
