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INFLUENCE OF PH AND OXIDATION-REDUCTION (EH) POTENTIAL ON THE DISSOLUTION OF MERCURY-CONTAINING MINE WASTES FROM THE SULFUR BANK MERCURY MINE
Citation:
Randall*, P M., S. Chattopadhyay, AND J. A. Ickes. INFLUENCE OF PH AND OXIDATION-REDUCTION (EH) POTENTIAL ON THE DISSOLUTION OF MERCURY-CONTAINING MINE WASTES FROM THE SULFUR BANK MERCURY MINE. Presented at 2003 Society for Mining, Metallurgy, and Exploration (SME) Annual Meeting, Cincinnati, OH, 02/24-26/2003.
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. Characterization and leaching tests 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 the solubility and release of Hg from the waste materials under controlled conditions. The data will be used to predict the mobility of the Hg present at the SBMM and used for considering remediation options.
Tests were conducted with waste rock and roaster tailings that were homogenized and sieved to achieve particle size between 150 :m and 600 :m. The moisture from the samples was removed as per ASTM Method D2261-80. Solubility and release of mercury at different pH (2-11) 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 tests, solubility and release of Hg 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 solubility of Hg was also determined by conducting tests in the presence of Fe(NO3)3?9H2O at different pH and Eh values. 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 solubility increased as the equilibrium pH of the suspension increased until a pH value of 10.65. Thereafter, the Hg solubility decreased sharply. Eh of the suspension also plays a significant role in Hg leaching. The Hg concentration, in the presence of Fe, decreased significantly (about 1/10th to 1/100th). Kinetic results show a relatively slow rate of Hg release in the presence of ferric ions.