Rare earth element patterns as process indicators at the water–solid interface of a post–mining area

Geochemical behavior of rare earth elements in acid drainages: Modeling achievements and limitations

“…Interestingly, almost all the solid samples did not reflect any Ce anomaly, as it is reflected by Ce/Ce* ratios between 0.95 and 1.13, except for some samples from Odiel and Tinto catchments (PO, AG and DB), which showed values higher than 1.3. The partial/ total Ce 3+ oxidation to Ce 4+ occurs in acid waters with the presence of high load of Fe and oxic conditions (Bau, 1999;Grawunder et al, 2018;Leybourne and Johannesson, 2008). According to laboratory experiments (Lozano et al, 2019c), REE sorption on schwertmannite occurs significantly at pH values higher than 5 (pH higher than 4 for Sc), and consistently, no REE was detected in three samples of schwertmannite precipitates (averaged as AG-r in Table 4) where the pH of the coexisting water ranged from 2.8 to 3.4 (AG and AG-mix1 in Table 1).…”

Rare-Earth Elements as Natural Tracers for In Situ Remediation of Groundwater

“…2 REE patterns in groundwater were previously examined in the context of understanding problems such as regional mixing; 3,4,9−12 upward migration of groundwater through fractured rock; 13−15 upward migration of groundwater from shale gas development and underground carbon sequestration; 16−18 assessing radionuclide migration; 19 and, for better understanding groundwater impacted by mine waste materials. 20,21 REE patterns (i.e., total abundance and shale-normalized profiles) in groundwater are the result of pH-redox conditions, solid−water interactions, and aqueous complexation reactions. Interpretations of REE patterns have mainly focused on differentiating between source-related and process-related controls.…”

“…Results from this previous study indicated that groundwater REE patterns could be used to detect features of contaminant sources as well as formation and dissolution of secondary phases in subsurface solids. 21 A common question to answer during performance monitoring of in situ groundwater remediation is whether water has, in fact, passed through and interacted with the emplaced/injected reactive materials used for contaminant removal. This issue becomes especially important in situations where contaminant concentrations in regions hydraulically down-gradient of treatment zones fail to decrease within predicted timeframes.…”

“…The rare-earth elements (REEs; La to Lu, excluding Pm) have been widely used as natural tracers in studies of regional groundwater migration and groundwater–surface water interactions. − The application of REEs as natural tracers takes advantage of their uniform trivalent charge, similar ionic radii, and within-group fractionation behavior that is controlled by aqueous complexation and reactions at the mineral–water interface . REE patterns in groundwater were previously examined in the context of understanding problems such as regional mixing; ,,− upward migration of groundwater through fractured rock; − upward migration of groundwater from shale gas development and underground carbon sequestration; − assessing radionuclide migration; and, for better understanding groundwater impacted by mine waste materials. , …”

“…REEs have not been extensively used in the evaluation of groundwater remediation technologies. However, Grawunder et al examined long-term REE patterns in shallow groundwater at a uranium leaching site following mine closure and remediation. Results from this previous study indicated that groundwater REE patterns could be used to detect features of contaminant sources as well as formation and dissolution of secondary phases in subsurface solids .…”