Removal of Radioactive Ions from Nuclear Waste Solutions by Electrodialysis

Abstract

Removal of radioactive ions was studied from low and medium level radioactive waste solutions by electrodialysis using ion exchange membranes. The test solutions contained 137Cs+, 90Sr2+, 106Ru3+ or fission products (F.P.) as active ions and NaCl, Na2SO4 or Ca(NO3)2 as inactive coexisting salts. The decontamination factor of the active ions was in the order: 137Cs+ (greater than 99%) 90Sr2+F.P. 106Ru3+. The dialysis time required to attain the saturation was the shortest for monovalent cations K+, Cs+ and Na+, intermediate for divalent cation Sr2+, and the longest for trivalent cation Ru3+. The ratio of the decontamination factor of an active ion ηA to the desalination factor of an inactive ion A+ was nearly equal to unity for 24Na, 42K, 137Cs and S),Sr. On the other hand, the apparent selective permeability of an active ion (A+) against Na+ ion, TA+ was higher than unity for all the active ions tested, and was in the order of 137>Cs90Sr>42>K24Na, where TA Na+ is defined by the ratio of γA to γNa+ with γA being the ratio of dilution of A in the diluate and γNa+ being that of Na+ in the same diluate. The decontamination factor of the active ions did not depend significantly on the species and concentrations of the coexistent salts or on the concentration of the active ions.