Mercury Mobilization from Contaminated Creek Bank Soils and Stabilization using Engineered Sorbents

As a global environmental pollutant, mercury (Hg), threatens our water resources and presents a substantial risk to human health. The goal of this research project was to evaluate the immobilization of Hg on sorbents to reduce ambient Hg concentrations in water leaching from contaminated East Fork Poplar Creek (EFPC) (Oak Ridge, TN, USA) soils. Using flow-through columns, we determined the potential of different kinds of engineered sorbents (i.e., ThiolSAMMS®, biochar, SediMiteTM, OrganoclayTM PM199) to reduce mercury fluxes from contaminated EFPC soils. The effectiveness of the sorbents in this experiment was determined based on the rate of Hg sorbed and the percentage of Hg removed as compared with the amount of Hg applied; i.e., a mass balance. All the sorbents removed Hg to a certain extent, but none of the sorbents was able to remove 100% of the Hg to which they were exposed. From all the evaluated sorbents, ThiolSAMMS® showed the highest percentage of Hg removed (~87%). A non-reactive Br^- [bromide] tracer experiment was conducted to determine the hydraulic properties of the sorbent columns and to ensure that no flow along the walls or preferential flow occurred. Br^- was also applied to qualitatively determine how quickly Hg breaks through the sorbent columns, most of the sorbents had a Hg breakthrough within the first 3 pore volume (PV). ThiolSAMMS® was the only sorbent to have retardation on the Hg breakthrough (7 and 70 PV). To determine mechanisms for the Hg uptake by the sorbents, we conducted a set of analyses to identify changes in concentrations of chemical constituents entering and exiting the sorbent columns. We noticed no difference in pH, anions (Cl [chloride], SO4 [sulfate], NO₃ [nitrate]) or metals (Al [aluminum], Fe [iron], Mn [manganese] and Si [silica]). We also observed that the concentrations of dissolved organic carbon (DOC) were statistically different for biochar and OrganoclayTM PM199. Specific UV absorbance (SUVA) showed statistically significant differences for biochar. The differences in DOC and SUVA were minimal, overall, suggesting that the mechanism for Hg uptake remains unknown.