In their previous papers, the authors reported the amount and the crystal-form of those impurities which adhered to and were contained in the crystals of vacuum salts and Australian solar salts. In this paper, the authors conducted a study in the same way on those of Chinese solar salts which were inferior in quality to those of Australian and American salts. 1. Chinese solar salts were composed of 94-95% NaCl, 0.5% insoluble matters and 3% water, which were inferior to those of Australian and American salts. No remarkable change in the quality of the salts has been observed in recent years. 2. Impurities in crystals of Chinese solar salts were 0.01% insoluble matters and 0.67% water, which were greater in amount than those of such a high-quality solar salt as American. The ratio of the impurities in crystals to the total was 18-30%, which was shown as the limit of the quality improved by washing. 3. The composition of the mother liquid in the crystallizing pond of the salt-field was estimated at 10-43mol/l, 000mol H2O and was shifted from the concentrating process of sea water. This showed that the mother liquid in the pond was re-used several times after the crystallization of salt took place. 4. The crystals of Chinese solar salts were 1-10mm in grain-size and were not transparent. They contained 4-100μm cavities and 10-50μm CaSO4·2H2O in crystals. 5. The soluble and insoluble impurities of Chinese solar salts could be decreased by 50-60% by washing them with brine after they were crushed.
The electrodialytic method with ion exchange membranes has been mainly used as the concentrating operation or the desalting operation of brackish water. As yet, an agreed view about ion transfer within the electrodialytic equipment has not been given. As one of the fundamental researches, therefore, the authors investigated the influence of concentration of feed solution, current density, flow velocity, electrolyte and temperature to the ion transfer in electrodialysis. The measurement of some operating factors on the ion transfer was carried out for one pass of solution through the electrodialytic equipment with ion exchange membranes and without spacers. From this experiment, it was found that the contribution of the concentration difference between the concentrated solution and the desalted solution to the mass flux caused by the diffusion was negligible as compared with the contribution by the current density; namely, the mass flux was proportional to the current density, and the current transfer coefficient was shown by Eq.(8). In addition, this relation was valid even when the concentration of feed solution and the electrolyte in the electrodialytic equipment were changed. About the effect of temperature, it was found that the mass flux of ion transfer could be increased by lowering the temperature during the electrodialysis.