Trace Metal Enrichment in the Colloidal Fraction in Soils Developing on Abandoned Mine Spoils

The release of colloid-bound trace metals from abandoned coal mine spoils can potentially be a significant source contamination during weathering. We examined the size-dependent enrichment in spoil samples using centrifugation and acid extraction to compare metal loading bulk colloid fractions. A combination X-ray diffraction (XRD), scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), focused ion beam (FIB) sectioning selected colloids for transmission (TEM) analyses was used determine morphology elemental mineral composition at micro- nanoscales. In contrast soils, primary Fe-sulfides (up 11%) secondary Fe(III)-bearing phases 5%) were portion mineralogy. Secondary Fe-(hydro)oxides (hydroxy)sulfates enriched Mn, Ni, Cu, Zn, these showed stronger correlations Fe fraction (R2 0.58, 0.77, 0.94, 0.81, respectively) than 0.40, 0.09, 0.84, 0.62, respectively), indicating that Fe-bearing are likely major trace-metal-bearing phases. results this study will help design better remediation projects account underappreciated mode contaminant transport.