A study was conducted to make a comparison between the concentration process of brine obtained by ion-exchange membrane method (brine I) and that of brine obtained by evaporation method (brine II), from sea water. It wasconducted mainly in the crystallizing field of sodium chloride at the boiling point under the atmospheric pressure. The brine I excluding the brine which contains more sulfate ion than the equivalent of calcium ion, possessed less sodium chloride the brine II at the saturation point with sodium chloride. Furthermore, the amount of sodium chloride contained in the brine I showed a more rapid decrease when further evaporated. Accordingly, the amount of water to be evaporated from the brine I to separate the same ratio of sodium chloride would be less than that to be evaporated from the brine II. In the brine which has a little amount of calcium sulfate and common ion salts (calcium chloride and magnesium sulfate), no deposition of calcium sulfate was observed before the saturation point with sodium chloride. All the depositted calcium sulfate was found to be hemihydrate. The brine I contained more potassium ion in its mother liquor as compared with the brine II, and therefore the brine I would be suitable to the manufacture of potassium salt.
In their previous paper (This Journal, 19, 164-7 (1965)), the authors reported that the composition of ion-exchange membrane brines could be roughly divided into two 6-component systems; a-type brine belonging to NaCl-KCl-MgCl2-CaCl2-CaSO4-H2O and b-type brine belonging to NaCl-KCl-MgCl2-MgSO4-CaSO4-H2O. When the authors considered the process of concentration of ion-exchange membrane brines by phase rule, they omitted CaSO4. from the consideration on the assumption that CaSO4 contained in these brines is entirely precipitated out prior to the precipitation of NaCl. Also, they simplified the equilibrium diagram on the assumption that the equilibrium system is always saturated with NaCl, just as in the case of sea-water concentration. In the present paper, the authors determined the kinds of precipitated crystals and the changes of liquid phase components during the process of thermally evaporating the brine which was supposed to have representative composition of a-type and b-type brines at the temperature of 25°C. In this case, they used for the a-type brine the equilibrium diagram on the triangular coordinate, and for the b-type brine the equilibrium diagram on the stereo-geometric axis for graphicalcal culation. Also, the composition of the liquid phase obtained when NaCl crystals begin to precipitate was graphically calculated from the NaCl solubility and the NaCl concentration obtained when KCl crystals begin to precipitate. As is shown by the results of the calculation of the a-type and the b-type brines, about 97% of NaCl content was precipitated as pure crystals before the volume of mother liquor was reduced to approximately 1/10 of the original brine. Then, the precipitation took place in the order of KCl, MgCl2·KCl·6H2O. The compositions of precipitated crystals in each stage of concentration were also approximately the same, and the liquid-phase compositions were analogous except for the difference between CaCl2 and MgSO4·From these facts, the authors reached the conclusion that in so far as the concentration is not so much advanced, the properties of brine such as the boiling point, specific heat, etc. may be of nearly the same value.
In his previous paper, the author reported that calcium salts crystallized from de-magnesiumed and de-calciumed brine were 2Na2S04·CaSO4·2H2O and glauberite. In this paper, the author analyzed the composition of precipitates and their mother liquid taken from 10 salt manufacturing factories, and studied the crystal state by X-ray diffraction and thermal gravimetric analyses. The results obtained were discussed from phase equilibrium on both solid and liquid phases. The following were the results thus obtained; 1. Precipitates of mother liquid are composed of sodium chloride and one or more than one of calcium sulfate hemi-and di-hydrates, polyhalite and kainite. 2. The solid phase is closely related to the composition of mother liquid. 3. Calcium hemi-and di-hydrates or glauberite crystallized from the mother liquid in the early stage of concentration near the composition of sea water in Janecke's figure. 4. Polyhalite alone, or polyhalite with single crystal of calcium sulfate was found in the mother liquid in the late stage of concentration.
The authors made a study on the impurities of common salt by dividing them into two groups; e. g., the impurities adhered to the surface of crystals (on crystal)(this will be reported later.) and those contained in the crystals.(in crystal) This paper reports the results of the study the authors made on those impurities contained in the crystals by chemical, X-ray and thermo-gravimetric analyses including microscopic observation. The resuts were as follows: 1. Those impurities contained in the crystals were K+; 0.013-0.033g, Mg++; 0.007-0.017g, Ca++; 0.003-0.014g and SO4--; 0.022-0.069g per 100 gram sample, respectively. 2. 70-80% of total potassium ion contained in the crystals was considered to exist as a form of potassium chloride. 3. The result of microscopic observation showed that almost all the calcium ion was contained as a form of calcium sulfate. Much more calcium sulfate was contained in those crystals of salt produced by ion-exchange membrane method (0.109-0.641g/100g) than in those of salt produced in ordinary salt fields (0.010-0.044g/100g). 4. The amount of cavity (hole containing mother liquid in the crystals) was measured by gravimetric analysis and found to be 0.15-0.24g/100g except the crystals of salt made by ion-exchange membrane method. 5. There was found a corelation between the density of mother liquid and the amount of cavity therefrom. Namely, as the mother liquid was concentrated, more cavity was contained in the crystals.
In order to control suspended matters in sea water to be fed to the salt-making factory operated by ion-exchange membrane's method, the authors studied the measurement method for the turbidity of sea water, the relations between the turbidity and each of other characteristics of the suspended matters, effects of particle size and composition of the suspended matters on the turbidity, and obtained the following results: The light scattering method was found to be an appropriate method for the measurement of suspended matters in sea water. By improving the JIS' light scattering method, the measuring sensitivity was increased about ten times, and the turbidity as low as 0.002 ppm could be measured. The standard turbidity solution prepared by JIS' method was found to be most appropriate, and its mean particle size was 2.7μ. The strength of light scattering reached a maximum of about 2μ. However, it decreased as the particle size deviated from 1 to 3μ, and the turbidity value also decreased. The turbidity, the dry weight of suspended matters, the particle size and chemical composition of suspended matters in sea water samples collected at Iwaki (Fukushima pref.), Oku (Okayama pref.), Sakaide (Kagawa pref.) and Odawara (Kanagawa pref.) were measured by the improved light scattering method, by filtration with membrane filter arid drying at 50°C, by Tyndall light method, by Andreasen pipette method, and by chemical and X-ray spectrometric analysis, respectively. By examining correlations between the turbidity and each of other characteristics of suspended matters, it became possible to estimate the other characteristics from the turbidity value. The sea water collected at Iwaki contained many decomposition matters of diatoms, and the filtrated sea water was found to contain fine coal dust. The sea water obtained at Oku contained many animate matters, while the sea water at Odawara showed higher content of ferric compound.