In this paper, a study was conducted on the method of recovering potassium from sea water andbrine by using zirconium polyphosphate (ZPP) and zirconium phosphate (ZP), and then crystallinezirconium phosphate (CZP) as an inorganic ion exchanger.
For preparing polyphosphate, there were used Na-tripolyphosphate, Na-hexametaphosphate, andNa-polyphosphate which was prepared by heating NaH₂PO₄·₂H₂O for three hours at 550°C and 650°C, respectively.
1. The total ion exchange capacity of the resulting ZPP was in the range of 4 to 5mg-equiv, /gof exchanger, and that of ZP exchanger was enhanced with an increase in the molar ratio ofPO4/Zr of the initial solution. It was about 5 mg-equiv./g when the molar ratio was 2.5: 1.
2. It was possible to selectively adsorb the potassium dissolved in sea water and brine by ZPand ZPP exchangers.The amount of adsorbed potassium for the zirconiumpyrophosphate and zirconium-hexametaphosphate was larger than that of sodium, and in selective adsorption, potassiumproved to be the best of all exchangers used.
3. Also, chromatographical separation was possible between sodium and potassium by which theconcentration and volume of desorbent for the column were exchanged. Therefore, thepercentage of potassium ion against the total cation (Na+K+Mg+Ca) in the desorbent was enhanced to about 80%.

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To evaluate the merits of electrodialytic concentration of the waste brine discharged from a seawater desalting plant by muiti-stage flash (MSF) process, or of the sea water of higheremperature discharged from the condenser of a steampower station, the authors carried outxperiments on the electrodialytic concentration of sea water of different temperatures andprepared solutions of different concentrations and temperatures, using a smaller electrodialysis, apparatus and examined the effects of the concentration and temperature of feed solutions and ofcurrent density on the concentration characteristics. Results obtained were as follows:
1. In case the electrodialytic concentration of sea water of higher temperature is done, the following merits cen be expected:
(1) As the temperature of feed solution becomes higher, the cell voltage and the electricenergy consumption decrease.
(2) As the water splitting becomes harder to occur, as compared with the electrodialyticconcentration of natural sea water, the risk of scale formation decreases.
(3) Because of (2), the operating current density can be raised and approached to the optimum value.(At present, the opeating current density in electrodialytic concentration of natural sea water is obliged to be set lower than the optimum value to prevent watersplittng and its resulting scale formation.)
(4) Because of (3), the output of NaCl shows an increase.(This means that, if theoutput of NaCl is definite, the unit of the electrodialysis apparatus can be reduced.)
2. In case of the electrodialytic concentration of solutions of higher concentration and highertemperature, the following merits can be expected, as in that of the waste brine obtained fromMSF process plant:
(1) As the temperature and the concentration of feed solutions become higher, the cell voltage and the consumption of electric energy decrease.
(2) As the water splitting becomes harder to occur and the permselectivity of bivalent ions decreases, the risk of scale formation decreases.
(3) Because of (2), the operating current density can be raised and approached to the optimum value.(Optimum current density in the electrodialytic concentration of the waste brine from MSF process plant is estimated to be higher than the value in the electrodialytic concentrarion of sea water of higher temperature.)
(4) Because of (3), the concentration and the quantity of concentrate and the output ofNaCl increase.
(5) As the concentration of the concentrate increases, the amount of water to be evaporatedin the crystallization process is expected to decrease. This brings about a decrease in the crystallization cost.

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