Effects of colloidal particle size on the geochemical characteristics of REE in the water in southern Jiangxi province, China

Abstract

The small watershed of southern Jiangxi province, embodying much detailed information about the origin and behavior of rare earth elements (REE), is a typical region enriched in REE in China. In this study, the dissolved rare earth elements (DREE) geochemistry affected by colloidal particle size (<0.45 μm, <0.2 μm), was first analyzed in a small watershed with high REE background. The REE geochemical characteristics were studied comparatively in both the regions affected by REE or not. With deceasing pore size (reducing more colloidal particles), the following results were found: (1) the total DREE concentrations of the filtrates decrease from 0.533 to 0.357 μg/l, mainly because the filter membrane with smaller pore size can remove more REE-rich colloidal particles from the water samples. (2) Two types of PAAS-normalized-DREE patterns changed differently. The relatively flat pattern, in the area without REE minerals influence, converted from slight light REE (LREE) enrichment to weak HREE enrichment. This should be due to the decreasing adsorptive ability of REE from La to Lu on the colloidal particles. The HREE enrichment pattern in the area affected by REE minerals had no obvious change, which may be resulted from the preferable complexion of LREE with $${\text{SO}}_{4}^{2 - }$$ in the extraction liquids or from anthropogenic factors. (3) Both negative Ce anomalies and negative Eu anomalies were weakened and positive Eu anomalies became stronger. It evidenced that larger colloidal particles (0.2 < d < 0.45 μm) adsorbed less PAAS-normalized Ce relative to its neighboring elements (PAAS-normalized La and Nd). This study will be useful to future-related research in a watershed impacted by multiple factors.