Three kinds of membrane cells (a),(b) and (c), as shown in Fig. 1 and Fig. 2 were experimentally produced to improve the filterpress-type concentrator. The effective membrane area of these cells were expanded further than that of the old type without providing internal conduit holes to the surface of the membrane. As the result of experimental use of these cells in an industrial scale apparatus, the authors reached the following conclusions: 1. The cell (a) proved it difficult to produce its gasket, and its concentrating characteristics were not favorable. 2. The cell (b) proved it easy to produce its gasket, and its concentrating characteristics were favorable. However, it had such a defect as the spacer of flow-paths was fragile, and it could not prevent an increase in the flow-resistance resulting from the deposition of suspended matters of sea water. 3. The cell (c) which was of the simplest structure proved it easy to produce its gasket. In addition, the leakage of liquid was little, and flow-characteristics and concentrating characteristics were favorable. However, it was presumed that the leakage of the current increased a little due to its wider flow-path than the old type. 4. The use of a thickness-adjustment-gasket in the cells (b) and (c) did not make it difficult to assemble membrane packs. Therefore, the use of thickness-adjustment-gasket was judged to be the most appropriate way for making the effective membrane area larger. 5. The experiments demonstrated that such a most rational and desirable cell-structure as the cell (c) could be produced by combining the membrane having no conduit-holes with the thicknessadjustment-gasket and the plane gasket having wider (simplified) flow-paths. 6. Even when the sea water which had been filtrated by sand or diatomaceous earth filter was fed to the apparatus, a farily large amount of suspended matter of the sea water was found to stick to the surfaces of the membrane and the spacer. However, the cell (c) with its flow-path expanded showed a less increase in the flow-resistance caused by such deposits as compared to the cells (a) and (b). 7. When the pH of sea water was adjusted to 5-6 by addition of hydrochloric acid before the sea water was fed to the apparatus, or when the pH of circulating brine was adjusted to around 4 by addition of hydrochloric acid also, there was no deposition of calcium carbonate. This was also true of a long-run operation which was done under such conditions as 5 amp/dm2 0f current density, 30% recovery of sodium chloride, and 14-25°C temperature of seawater.
The authors conducted a study on the properties of both the FAC which was available on the general market and the FAC which had been prepared by varying the compositions of iron and ammonium. The study aimed at investigating the colors of their aqueous solutions, the color of salt with FAC added, changes in habits of sodium chloride caused by FAC, and the anti-caking effects of the FACs. A further study was made on the decoloration of the commercially available FAC and changes in its anti-caking capacity. The following were the results obtained from these studies: 1. The aqueous FAC solution changed its color from yellowish green to dark brown in accordance with an increase in its pH. The absorbance of the solution at 520 mμ was the minimum at pH 5. 2. When a FAC having a greater absorbance at 520 mμ was used, the color of the salt with the FAC added developed in accordance with the increase of whiteness (ΔR). 3. When treated with active charcoal, the commercial FAC changed its color from brown to yellowish green. and the absorbance of its aqueous solution at 520 mμ became lower. However, no difference was observed in the white ness (ΔR) of the sait with 20-100ppm FAC added, between the treated and untreated ones. When the aqueous solution of the commercial FAC having little anti-caking effect was decolored, the pH of the solution showed a rise according to an increase in the anti-caking capacity. 4. When the aqueous sodium chloride solutions containing FAC at pH 8.5-9.0 were concentrated naturally on a slide glass, fine crystals of sodium chloride were produced. This showed that the TAC had an anti-caking effect of common salt changing habits by impurity. It was also shown by scanning electron microscopic observations that the fine crystals treated with ferrocyanide ions were different from those treated with the FAC. 5. The anti-caking effect of the FAC increased in proportion to the increase of pH, and the absorbance of its aqueous solution at 520 mp showed a rise making brown the color of salt with the FAC added.
Anti-caking ability of NTA-amide was examined by pressure and absorption-desorption caking tests. And the following results were obtained; 1. NTA-amide was found to have the effect of habit change on the crystallization of sodium chloride. Therefore, it was classified as an anti-caking agent by habit change. 2. Appreciable anti-caking effect of NTA-amide was expected with the addition of 5 ppm. The anti-caking ability was increased till 10 ppm then decreased gradually as the increase of the amount of NTA-amide. 3. NTA-amide decomposed at the temperature above 157°C. The anti-caking ability was not decreased, when the sample salt added with NTA-amide was dried below 140°C. 4. Anti-caking ability of NTA-amide was disturbed to some extent by potassium, magnesium and sulfate ions. 5. Anti-caking ability of NTA-amide was not decreased till 10 cycles of absorption-desorption caking test.
Desalination membranes of 6-Nylon were prepared by casting method. The Nylon solution was spread thinly on a glass plate, and the solvent was evaporated at a constant temperature. The film cast was immersed in water and then cured. The casting solution was composed of 6-Nylon (30-35%), formic acid (35-45%), and m-cresol or o-chlorophenol (20-30%). Membranes of better performance were obtained when the evaporation of the solvent was done at a high temperature (100°C) for a short period (3-4 min). Various curing processes were examined, but the curing in steam was found most effective. The rejection of the membrane which had been evaporated for 5 minutes at 100°C and cured in steam, showed 78% for Na+ ion (Raw solution: 0.05 mol/liter NaCl, Operating pressure: 50kg/cm2), but the amount of the flux was not very large.