Mineralogical factors causing underestimation of K_d values calculated from radiocesium interception potential

Abstract

The radiocesium interception potential (RIP) was developed as an indicator for frayed edge sites (FES) present in soils and minerals and is widely used to measure soil's ability to retain radiocesium. However, the limiting factors for using RIP to predict radiocesium dynamics in soil have not been adequately investigated. This study aimed to measure RIP using artificially weathered biotite. The solid–liquid partition coefficient (K_d) was determined, and the estimated K_d was calculated using RIP and K⁺ or NH₄⁺ concentrations in the liquid phase. The results consistently showed that the estimated values were lower than the measured values, particularly as the K⁺ or NH₄⁺ concentration in the liquid phase increased. The findings strongly suggest that changes in the swelling state of the solid phase, in combination with the composition of the liquid phase during K_d measurements, play a vital role in the variation of K_d, an aspect that is often overlooked.