A study of Ion Adsorption type Deposit REE enrichment in regolith using reactive transport model sim

Abstract

Rare-earth element (REE) ion-adsorption type deposits (IADs) are important REE resources with features such as easy extraction of REEs, abundance of HREE, and low involvement of radioactive elements. However, there has been no quantitative discussion of the formation process of the concentration patterns seen in the vertical profiles of the IADs. In this study, the vertical migration of REE is reproduced using a one-dimensional reactive transport model to examine the factors that contribute to the formation of REE concentrations in the IAD. Core samples of weathered granite from Ishikawa-machi, Fukushima Prefecture, Japan, collected by hand auger method were used for the simulation. XRD analysis of minerals, ICP-MS measurement of REE concentrations in acid-decomposed samples, XRF bead method measurement of major elements, and Y speciation analysis by EXAFS were conducted on the sample and confirmed that REE concentrations as IAD were occurring. The K_d of ⁸⁸Y was determined for this sample using pore water, and simulations were performed based on the K_d. The obtained results were compared with the erosion rate of the surface layer and discussed.