1977 Volume 31 Issue 4 Pages 164-178
In Japan, the common salt is made in seven factories by the evaporation of concentrated sea water, so called ionic brines, made by electrodialysis with ion-exchange membranes, in vacuum pans. As the ionic brines thus made contained little sulphates, so they may be, practically assumed to be the mixed solutions of chlorides. Then, the treatments of ionic brines in salt factories, such as, deposition of NaCl by evaporation and salts depositions by cooling the hot mother liquor and so on, may be graphically calculated with the phase diagrams for five component system: Na+, K+, Mg2+, Ca2+ Cl--H2O.
The author reported in his previous paper,method for computation of kind of salts deposited and amounts of their deposition, in case of cooling 110°C evaporated mother liquor to 25°C.
In this paper, the author studied the general solution of this problem, namely, graphical calculations for evaporations of ionic brines of any composition at any temperature, and cooling the mother liquor to any temperature.
The studies were done in three steps. At first step, the compositions of ionic brine were assumed that the concentration of NaCl, MgCl2 and CaCl2 remained constant, but only KCl changed. By this means, innumerable compositions of brine could be considered. For example, evaporation of brine A (Fig.-1) at 110°C, the mother liquor for such innumerable brine must lie on the line E1A′. Among them, four points, namely A′, A1′, A2′′ and A3′′, were found to be most important in relations to the lines gh and ij. Graphical calculations were made of these four points, the compositions of cold mother liquor ABB, A1B, A2B and A3B were found (Table-1, Table-2). From the positions of these points in the diagram, amounts of H2O evaporated, NaCl deposited by evaporation and amounts of salts deposited by cooling hot mother liquor were calculated (Table-3). For other brine B, D and E, the same calculations were made (Fig.-2). With so obtained sixteen values, the relation of KCl and NaCl deposited vs. KCl concentrations in the brine were shown in a graph (Fig.-3). In the graph, sixteen points for KCl and those for NaCl lied on straight lines passing the origine. So the relation might be expressed in two general formulas: y=ax and z=bx, where y and z mean the amounts of KCl and NaCl deposited, x means the concentration of KCl in the brine, in g/kg brine, and a and b were constants, namely 0.761 and 0.252. The reliability of these formulas were tested, and found, that, at least, they had reliability of two available cyphers (Fig.-4, Table-4).
As the second step, ionic brine was evaporated at 110°C, to KCl saturation, and the hot mother liquor thus obtained was cooled to 90°C, 70°C, 45°C and 25°C (Fig.-5). The amounts of KCl (y) and NaCl (z) dep sited were also found to be in relation to the concentration of KCl (x) in the brine: y=axandz=bx, where a and b were constants depend on the cooling temperatures tc (Fig.-6, Table-6).
As the third step, ionic brine was evaporated at 90°C, 70°C, and 45°C to the saturation of KCl and hot mother liquor separated from NaCl crystals was cooled to 25°C (Fig.-7). The amounts of KCl (y) and NaCl (z) deposited were found to be in relation to concentration of KCl (x) in the brine: y=ax and g=bx, where a and b were the constants depend on the temperature of evaporation th (Fig.-8, Table-7).
