Geochemistry and Implications of Rare Earth Elements in Arsenic-Affected Shallow Aquifer from Jianghan Plain, Central China

Jianghan plain has been determined as a new endemic arsenic-poisoning area in the southern China. In order to understand the role of rare earth elements (REE)on arsenic mobilization in groundwater from the Jianghan plain, REE concentrations were measured in 114 groundwater samples and 9 sediment samples from the shallow arsenic-affected aquifer system and the REE speciations along the groundwater flow path were caculated by the hydrogeochemical PHREEQC simulation. The results indicate that the REE concentrations range from 0.032 to 0.843 μg/L. The groundwater exhibite the enrichment of LREE and dramatically positive Eu anomalies, and the Eu anomalies are positively correlated with As concentration. The REE speciation mainly existes as LnCO₃⁺ and Ln(CO₃)₂^-, meanwhile the LnCO₃⁺ concentrations decrease and Ln(CO₃)₂^2- concentrations increased along the regional groundwater flow path. The distribution of REE concentrations was mainly affected by the complexation with HCO₃^- and the reductive dissolution of iron oxide minerals. The enrichment of LREE in the groundwater was affected by the REE distribution patterns of minerals in the aquifer and the preferential desorption with LREE of iron oxide minerals, and the REE speciation was controlled by the pH along the groundwater flow path. The Eu concentrations and positive Eu anomalies could indicate the enrichment of arsenic in the groundwater.