SORPTION AND MIGRATION OF RADIOIODINE IN SATURATED SANDY SOIL

Using I-125 as tracer, the migration of iodide and iodate in a solvent flowing steadily through saturated sandy soil was examined in column experiment and analyzed theoretically, with particular reference to th e effect of differences in pH value. Runs at pH 3, medial pH and pH 10 were performed to determine breakthrough data from radioactivity meas urements on the effluent solution. The results obtained from column ex periments indicated that, for the same pH, sandy soil sorbed iodate (( IO3-)-I-125) more strongly than iodide (I-125(-)), and that, for the s ame chemical form, more effective sorption is shown at lower than at h igh pH. This indicated that the sorption behavior of iodine in sandy s oil depended significantly on their chemical form and on pH-i.e. the h ydrogen ion concentration in the influent solution. The strong sorptio n of iodate under medial pH and pH 3-evidenced by the breakthrough dat a-was simulated numerically, based on mathematical expressions represe nting a combination of instantaneous (equilibrium) and limited-rate (n on-equilibrium) sorption processes. Unknown parameters incorporated in the model were determined by a procedure of fitting the mathematicall y derived curves to the observed plots for different experimental cond itions, as a result of which good agreement was obtained of the calcul ated curves with the observed breakthrough plots.