Assessment of Mercury Leaching Under Disposal Scenarios for Contaminated Demolition Debris and Treated Elemental Mercury

Abstract

Treatment and disposal of mercury and mercury-contaminated materials is a national need due to its human health and environmental toxicity. The Y-12 National Security Complex in Oak Ridge, Tennessee, houses four legacy buildings, with surrounding soils, requiring demolition that contain significant elemental mercury (Hg(0)) contamination. A Resource Conservation Recovery Act landfill has been proposed as the disposal method for the building debris and soil, necessitating understanding of the partitioning behavior of mercury. Additionally, large stores of Hg(0) exist in the U.S. in need of treatment and disposal. A proposed method for Hg(0) treatment is sulfur stabilization then coating with low-density polyethylene (LDPE). The efficacy of this disposal method is untested. This dissertation explores the leaching behavior of mercury in equilibrium with ordinary portland cement (OPC) as a surrogate for demolition debris and anticipated landfill backfill soil. pH-dependent testing was used to evaluate leaching, using Hg(0) and Hg2+, with OPC, soils, and a blend of 75% OPC-25% soil to provide first order approximations of partition coefficients. The assessment indicated partitioning of mercury to OPC of approximately 101 L/kg and to soils of approximately 103 L/kg at pHs between 8-13. Material-specific geochemical speciation models were developed using laboratory results to predict mechanisms controlling mercury in pH-dependent environments. Sorption to hydr(ous) ferric oxides (HFO) occurs in the acidic to neutral pH domain for each material, most notably in soil-containing experiments. In the alkaline domain the likely retention mechanisms are sorption to organics and to cement in soils and OPC, respectively. Predictions of landfill leachate concentrations were calculated using the first-order approximation partition coefficients (from laboratory experiments) to determine the potential range of mercury concentration in landfill leachate filled with demolition debris. The leaching behavior of a proposed Hg(0) treatment based on conversion to mercury sulfide and LDPE encapsulation was also tested. Results showed low-level mercury release from the pellets both with and without the presence of backfill soil. Additionally, swelling of some LDPE-coated pellets occurred, causing concerns for mercury release and disposal safety.