How the distribution coefficient of ²³⁸U in natural soils is affected by the method used to obtain the soil solution...

A systematic study on desorption of uranium in a natural soil has been carried out to reduce the level of uncertainty associated with the method employed to determine the values of the distribution coefficient (K_d). Generally, the operating method used to extract and analyze the soil solution determines the K_d values. Here, the centrifugation method has been used to obtain soil solution extracts. Several procedural parameters have been considered such as incubation time, the level of soil moisture relative to saturation (saturation degree) and centrifugation speed (equivalent to effective suction). In order to analyze the influence of soil structural characteristics, this study considers three grain-size fractions of soil: loamy coarse sand, loamy fine sand, and loam, all of which are obtained from a natural soil collected in a uranium mineralized area. Our results indicate that neither incubation time nor centrifugation speed influence the determination of K_d for uranium. The results also indicate that the level of soil moisture is the most important factor for determining ²³⁸U-K_d. It has been shown that the influence of moisture on K_d also depends on the structural characteristic of the soil. For the loamy coarse sand subsample, the moisture level during the incubation period showed a significant influence on the K_d. In addition, through the use of regression analysis, the pH was identified as the cofactor with the greatest influence on K_d of uranium.