Abstract
In Japan, the common salt-producing method with saline was entirely replaced by the new electrodialysis method with ion exchange membrane in 1972. This has resulted in a great change both in the chemical composition and the amount of bittern, the byproduct as well as the mother liquid of NaC1 deposits.
Bromine, potassium sulfate, calcium sulfate, potassium chloride, and various kinds of magnesium chloride are manufactured by evaporating the concentration of bittern.
The author has succeeded in obtaining potassium sulfate through the process of treating ionic bittern.
The apparatus of producing potassium sulfate was connected with a tripple-effect evaporator to form a unified system. In the process of treating decalcium bittern, we have established the processing formula of a greater effect than the sofar evaporation system.
The most important point of this report is an analysis on the preparation of potassium sulfate, K2SO4. The details of potassium sulfate preparation are as follows:
Because of the scarcity of natural potash resources in Japan, potassium chloride of low quality had been produced in bittern factories for use as fertilizer for sixty years. The author made a study on the preparation of potassium sulfate from bittern and succeeded fortunately in its industrialization.
The equilibrium diagram of J. H. van't Hoff or J. D'Ans for the five component system of oceanic salt, i. e., Na+, K+, Mg2+, Cl-, is not suitable for the full explanation of the phase rule phenomenon on the preparation of potassium sulfate.
J. H. van'tHoff treated isothermal equilibrium diagrams of four component system of oceanic salt as the reciprocal salt pair, K2Cl2+MgSO4→K2SO4+MgCl2. J. D'Ans treated oceanic salt as three axies, Mg, SO4, K2, and recognized that NaCl saturated in all cases. This phenomenon is so greatly complex that those diagrams conceived by the authorities are not able to explain the fact satisfactorily because Na+ cannot change freely and perfectly in the equilibrium diagrams owing to the lack of Na2. In order to make Na2, K2, Mg, SO4, Cl2 change freely and perfectly, the author felt it necessary to make use of the diagram of ternary prism system that was first reported by Dr. Shunpei Oka at the meeting of the Society of Salt Science held in Tokyo, Japan in May, 1959.
The author made an investigation on the graphical calculation of phase rule by using Dr. Oka's diagram, and thus devised to apply the calculations to practical use for industrialization. Those graphical calculations obtained from the author's study are shown in this report. The comparison of these graphical calculation data with the actual data of industrialization indicates that they are quite similar to each other in their tendency.
The outline of the actually-industrialized manufacturing process resembles the process employed by Stassfurt salt mine, which manufactures potassium sulfate from decomposition of kalimagnesia with potassium chloride and produces kalimagnesia by the double decomposition of magnesium sulfate with potassium chloride.
Kalimagnesia in this case, therefore, is a kind of medium double salt produced in the two-step reaction process. Magnesium sulfate, MgSO4·7H20 used to be produced from bittern by cooling with refrigerator in the salt-field bittern age. Nowadays, however, as there is not a source of supply of magnesium sulfate in ion-bittern, magnesium sulfate is obtained from magnesium hydroxide by treatment with sulfuric acid. Magnesium sulfate which is now used is of the following chemical synthesis, Mg (OH) 2+H2SO4=MgSO4+2H2O.
