Carroll, Jordan E. 1 ; McKnight, Diane M. 2 ; Rue, Garrett P. 3
1 University of Colorado/INSTAAR
2 University of Colorado/INSTAAR
3 University of Colorado/INSTAAR
Quantifying and understanding the transport of rare earth elements (REEs) in relation to heavy metals within acidic alpine rivers is relatively understudied. However, employing solute transport models, specifically One-Dimensional Transport with Inflow and Storage (OTIS) provide insight into the reactivity and transport of REEs. OTIS is a solute modeling system capable of predicting conservative behavior in rivers. The influence of pH on metal complexation, precipitation/dissolution and oxidation/reduction was investigated using simulations and parameter estimation to analyze data collected by synoptic sampling and tracer injection experiments. The Snake River is located along the Colorado Mineral Belt in Summit County, Colorado and drains into metropolitan Denver’s drinking water source – Dillon Reservoir. The Snake River is of particular interest due to its hydrological and geochemical similarity to other alpine streams impacted by acid mine drainage throughout Colorado.
In previous studies, most REEs behaved conservatively at lower pH and concentrations decreased as pH increased from 4.13 to 8.52 from upstream to downstream. Using size-partitioning experiments, the compositions of colloidal and dissolved phases were obtained to determine the dominant state of varying heavy metals and subsequent interaction with REEs. Fractionation experiments showed that REEs are proportionally more abundant in their dissolved form at low pH. The distribution between colloidal and dissolved phases increased as pH increased.
Modeling the transport of REEs of industrial importance will significantly resolve issues concerning acid mine drainage remediation and future mineral extraction. Remediation efforts must account for more extreme conditions than have been encountered in the past. Water treatment plants may need greater capacities and passive treatment schemes may require more extensive approaches to compensate for higher metal concentrations entering Dillon Reservoir.