Separation of Calcium-Ion and Potassium-Ion

Abstract

“Calcium chloride solution” is produced from bittern, by adding CaCl₂and Ca(OH)₂solution to bittern and separating gypsum and magnesium hydroxide, respectively. It is about 16% in concentration and contains about 1/10 (equivalent ratio) of potassium ion. Separation and concentration of potassium ion from “calcium chloride solution” by electrodialysis with ion exchange membranes was examined. Selective permeability of calcium- to potassium-ion (T^Ca_K) in such a solution with high grade of concentration and special chemical composition as “calcium chloride solution” was determined at various conditions.
Potassium ion shows usually preferential permeability to calcium ion in cation exchange membrane. T^Ca_Kwas determined to be about 0.33 for ordinary membrane and to be about 0.07 for permselective membrane on univalent ions at the optimum condition; current density 1.0A/dm²and temperature 25°C. For both sorts of membrane, values of T^Ca_Kbecome greater by increasing current density and by both elevating and descending temperature.
Compositions of desalted and concentrated solutions were determinedfor several degrees of concentration by calculation and experiment. Calculations were made assuming selective permeability mentioned above to be 0.1. Experiments were carried out with an equiprment having 9cm²of effective membrane area. Experimental values were appreciably different from calculated ones, owing chiefly to superior permselectivity of membranes and the migration of water accompanying electrodialysis.
Degree of desalting affected on the change of composition of solutions rather seriously. Potassium ion content in concentrated solution was smaller when degree of desalting was greater. Flow rate of the solution in desalting compartments might also affect on the composition of solutions.