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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:
Magar, V. S., S. Chattopadhyay, J. A. Ickes, K. Hartzell, J. Lipps, D. Janke, AND P Randall*. 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, DC, EPA/600/R-02/032 (NTIS PB2003-100710), 2001.
Impact/Purpose:
Information.
Description:
Mine waste rock and roaster tailings were collected from the Sulfur Bank Mercury Mine (SBMM) located in Clearlake Oaks, California. The site has been under investigation as a Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) site. Leaching profiles of SBMM waste rock and roaster tailings over a range of different pH and oxidation-reduction (Eh) conditions were performed. Each experiment has been designed to evaluate leachability of Hg from the waste materials under controlled conditions that may contribute to the destabilization of the waste rock. The data was used to predict the fate and stability of Hg present at the SBMM and incorporated into consideration for remediation alternatives.
Experiments were conducted with waste rock and roaster tailings that were homogenized and sieved to achieve particle size between 150 um and 600 um. The moisture from the samples was removed as per ASTM Method D2261-80. Leachability at different pH (2, 3, 4, 5, 6, 7, 8, 9, 10, and 11) conditions was measured. Also, the oxidation-reduction potentials of the leachate, which were subsequently converted to the corresponding Eh-values, were recorded under equilibrium conditions. In a separate set of experiments, leachability was measured as the Eh conditions were varied by controlling the rate of purging of the suspension with air, O2, N2, and H2 gases at constant pH-values. As iron is present in large quantities in mining wastes, the effect of iron (Fe) on leaching of Hg were also determined by conducting leachability studies in the presence of Fe(NO3)3?9H2O at different pH and Eh values. The concentration of Fe in each sample was the same as the Hg concentration as observed from the previous set of experiments where no Fe was added. After leaching, the suspended samples were filtered prior to Hg analysis. Hg was analyzed as per EPA SW846 Method 7470A. Turbidity of the filtrate, alkalinity, and acidity are being measured by using HACH 2100N turbidimeter, and as per EPA Methods 310.1 and 305.1, respectively. Results show that the Hg concentration increased as the equilibrium pH of the suspension increased until a pH value of 10.65. Thereafter, the Hg concentration decreased sharply. Eh of the suspension also plays a significant role in Hg leaching. The Hg concentration, in presence of Fe decreased significantly (about 1/10th to 1/100th). Finally, kinetic results show a relatively slow rate of leaching in presence of ferric ions.