In the present investigation, the authors determined the permselectivity of SO42- and Cl- through anion-exchange membrane in the ion-exchange transfer by NO3-. The results obtained were summarized as follows: When the concentration ratios of SO42- and Cl- in the original solution were constant, the transfer rate of SO42- and Cl- increases, respectively, with an increase in the concentration of NO3-, but the ratio of the transfer rate of the both ions was independent of the concentration of NO3-. The permselectivity coefficient of SO42- against Cl- was very small and approximately equal to that in electrodialysis. This value decreased with an increase in the concentration of the original solution. Also, the separation factor of SO42- against Cl- in the anion-exchange membrane showed a decrease with an increase in the concentration of the original solution. This tendency was very similar to that of the permselectivity coefficient. Thus, it was inferred from the above-mentioned facts that the mobility ratio of SO42- against Cl-in the membrane could be calculated from the value of the permselectivity coefficient and the separation factor. As the result of our calculation, the value proved to be about 0.5 notwithstanding the concentration of the original solution.
Common salt produced from the sea water that had been treated with caustic soda and milk of lime for precipitation of magnesium hydroxide, showed an abnormal caking tendency as compared with the salt produced from salt-field brine. The author, therefore, investigated the caking strength and examined the manufacturing process in order to reduce this caking tendency. Results obtained were as follows: 1. The common salt produced from the de-magnesium sea water proved to have a greater caking tendency than the salt produced from the salt-field brine. The caking strength was 1-5kg/-cm2 for the storage period of 6-12 months. 2. This high caking tendency is attributed to the fact that mother liquid containing less magnesium ion on the surface of salt crystals tends to dry when it is placed in low humidity, and when it is cooled it tends to precipite ateastrakanite (MgS04·Na2S04·4H20, hydrated double salt) transformed from loeweite and vanthoffite. This caused the salt to cake considerably.
In separation and concentration of potassium chloride by electrodialysis with ion exchange membrane from “calcium chloride solution” mentioned in previous report, effects of flow rate of the solution in desalting compartments and of degree of desalting on the composition of concentrated solution were estimated. The electrodialysis cell used was of 9cm2 in effective membrane area and consists of 4 concentrating compartments and 5 desalting ones. Membranes used were of the same as those in previous report, univalent permselective membranes. Desalting solution was circulated and raw solution was feeded continuously to the solution in circulating system. Effect of flow rate found to be little at 0.5-2.0cm/sec and that of degree of desalting to be serious. A bench scale test based on the above experimental results was done with a cell unit having 5 dm2-effective membrane area, 17-concentrating compartments and 18-desalting ones. Circulation system of desalting solution was also employed. Degree of desalting was set so that the concentration of calcium chloride in desalted solution may be rather high compared with that in raw solution. Current density, flow rate of the solution in desalting compartment and temperature employed were 1A/dm2, 3cm/sec and 11-13°C (equilibrated to the room temperature), respectively. Separation and concentration of potassium chloride were carried out satisfactorily. Volume of concentrated solution taken was about 1/10 of that of raw solution feeded, and recoveries of potassium chloride deposited from both of solutions by evaporation at the same conditions were calculated to be nearly equal. Electric power demand for electrodialysis was calculated to be about 1,100KWH/t-KCI.