Rare earth element patterns: A tool for understanding processes in remediation of acid mine drainage

Abstract

The distribution of rare earth elements (REE) was applied to study processes in remediation of acid mine drainage (AMD). The concentration of total REE is up to 3 mg l −1 in AMD. Normalization of REE concentrations in seepage and surface waters to Post-Archean Australian Shale (PAAS) shows strong enrichment of heavy REE. For the case of the studied AMD REE patterns are representative for the seepage location. Therefore, they can be used to identify (former) waste rock dumps as a source of valley sediment contamination. Results from percolation experiments and LA-ICP-MS measurements show that REE patterns of seepage water samples do not reflect the total REE pattern of the source rocks but are preferentially eluted from Silurian “Ockerkalk”. Along a flow path of the creek Gessenbach, REEs decrease in concentration and fractionate due to coprecipitation with Fe phases. REE patterns are also applied to the study of sorption/uptake of heavy metals by biomass. A strain with high potential for remediation purposes could be identified by incubating microbial strains isolated from the investigation area directly in AMD. Finally, for a contaminated soil with acidic pH and thus high availability of heavy metals to plants the transfer of heavy metals from soil to plants was studied by the use of REE patterns. For different herbaceous plants and trees different REE patterns were observed although the corresponding soil was identical. Concentrations of REEs are always higher in leaves than in shoots/branches. However, within one species REE patterns are quite similar for leaves and the corresponding shoots/branches.