Adsorption and Removal of Radioiodine in the Water Supply by Coprecipitation with Iron (III) Hydroxide

Abstract

The coprecipitation of radioiodine by iron (III) hydroxide flocculation method was studied as functions of pH and the concentrations of coexisting ions of the solutions for the removal of radioiodine on the water treatment system.
The pH of the radioiodine solution included chloline water as oxidizer and iron (III) nitrate was adjusted to pH 9 to 9.5 for the precipitation of iron (III), and then readjusted to pH 4 to 6. Thus the iodate ion was absorbed by the electrostatic action on iron (III) hydroxide particle surface. The adsorption property is affected by contents of coexisting anions. Sulfate ion prevented the adsorption of iodate ion on the iron (III) hydroxide. The radioiodine removal effect at pH 6 decreased by carbonate ion, since the isoelectric point of the iron (III) hydroxide located lower pH 8.5. However, by the coexisting anions, the coagulation and settling abilities of the iron (III) hydroxide in the slightly acid solutions were improved The removal rate of radioiodine was more than 95% at pH3 to 4 of the solution, in which the anions of the natural river water level of Japan (SO₄^2-, CO₃^2-<0.4, 30 mg/l) were coexisted.