Abstract
On the basis of his previous report on desalination process, the author presumed by means of calculation the conditions under which CaSO4-scale deposition took place, and confirmed the results of his presumption with those of his concentration experiments which were carried out for about 100 hours. As a consequence, the following were made clear:
1. On the surface of the cation exchange membrane, an increase in the desalination ratio caused a gradual increase in the concentration of Mg2+ and Ca2+, but the concentration of SO42- was kept almost unchanged. On the surface of the anion exchange membrane, on the other hand, the concentration of SO42- showed an abrupt increase, and Mg2+ and Ca2+ a gradual increase.
2. As a result, CaSO4-scale was expected to deposit on the anion exchange membrane first when the desalination ratio would reach 85%, but 95% on the cation exchange membrane.
3. The concentrating experiments suggested that CaSO4-scale deposition began between 80 to 90% of the desalination ratio, and that the scale deposited on the anion exchange membrane around 90%. Thus, the results of the experiments agreed with those of the above presumption, proving that it was possible to predict the beginning point of CaSO4-scale deposition by calculation of the desalination process.
4. CaSO4-scale crystals were confirmed to be CaSO4·2H2O by X-ray diffraction analysis.
