Interpolation of solid/liquid partition coefficients, Kd, for iodine in soils

Abstract

The measurement of K d is difficult for most radionuclides: a different value is expected for every different soil. This study explored a modification of the constituent- K d approach used to estimate K d in geological materials. Here we selected five soils of very different compositions, four were field soils and one was an artificial potting soil. The soils were blended together in ratios of 1:1, 1:3 and 1:1:2 for all possible (60) 2- and 3-soil combinations. The K d was measured for each soil and each of the combined soils using additions of stable iodine. Our hypothesis was that the weighted average of the K ds of the original, unblended soils, weighted by the blending ratios, would be a reasonable estimate of the measured K ds of the blended soils. The ratios of expected/measured K d values did not deviate significantly from unity (a geometric mean of 0.91) for the four field soils. This result suggests that K d in the combined field soils could be estimated by the weighted average K d for the constituent soils. The resulting variation is consistent with other estimation methods. The practical implication of this finding is that, with K d data for a few benchmark soils in a region, one could estimate K d for other soils. The potting soil did not conform, and there are several possible explanations for this.