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CHARACTERIZATION AND EH/PH-BASED LEACHING TESTS OF MERCURY-CONTAINING MINING WASTES FROM THE SULFUR BANK MERCURY MINE, LAKE COUNTY, CALIFORNIA
Citation:
CHARACTERIZATION AND EH/PH-BASED LEACHING TESTS OF MERCURY-CONTAINING MINING WASTES FROM THE SULFUR BANK MERCURY MINE, LAKE COUNTY, CALIFORNIA. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/R-02/032, 2001.
Description:
Clear Lake in northern California has received inputs of mercury (Hg) mining wastes from the Sulfur Bank Mercury Mine (SBMM). About 1.2 million tons of Hg-contaminated overburden and mine tailings were distributed over a 50-ha surface area due to mining operations from 1865 to 1957 (Gerlach et al., 2001). The SBMM includes an open, unlined mine pit, Herman Pit, which covers approximately 23 acres and is 750 feet upgradient of Clear Lake. Reynolds et al. (1997) analyzed water samples collected from Herman Pit and Clear Lake and reported the pH values at those locations as 3 and 8, respectively. The SBMM was placed on the Final National Priorities List (NPL) list in 1990. The site has been under investigation as a Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) site and has experienced some minor corrective actions. Clear Lake remains under a fish advisory due to the mercury contamination.
Mercury in contaminated soils is a unique pollutant that requires innovative remediation solutions. Conventional stabilization/solidification treatments cannot effectively reduce the leachability of Hg (Conner, 1990). As part of the remediation effort at the SBMM site, the USEPA is assisting in the development of treatment alternatives for waste material from the site. Waste materials consist of waste ore, waste rock, and roaster tailings. To support this work, leaching profiles of waste ore over a range of different pH and oxidation-reduction (Eh) conditions were performed. Chemical and biological processes affecting the mobility of metals may be initiated by altering the physicochemical environment (i.e., pH and Eh conditions). Important processes influencing the chemistry and availability of trace and toxic metals include 1) precipitation as insoluble sulfides under highly reduced conditions (Morel et al., 1974); 2) formation of discrete metal oxides and hydroxides of low solubility (Morel et al., 1974); 3) adsorption of colloidal hydrous oxides of iron and manganese, primarily in aerobic, neutral, or alkaline environments (Windom, 1973); and 4) complex formation with soluble and insoluble organic matter (Longathan et al., 1977).
Each experiment has been designed to evaluate leachability of Hg from the waste materials under controlled conditions in order to assess conditions that may contribute to the destabilization of Hg in the waste ore.
The objectives of this TO was to study a range of different pH and Eh values in order to evaluate the potential of SBMM waste ore to leach Hg.