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EPA/540/R-04/502
Stabilization
of Mercury in Waste Material from the Sulfur Bank Mercury Mine Innovative
Technology Evaluation Report
(PDF, 2266 Kb, 68 pp)
July 2004
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Abstract:
This report summarizes the findings of an extensive treatability study of three stabilization technologies for mercury immobilization on materials collected from the Sulfur Bank Mercury Mine (SBMM), located north of San Francisco, in Lake County, California. The SBMM site is believed to be contaminating the adjacent Clear Lake environment with mercury derived from historic mining practices at the site. The study was conducted as a joint effort between EPA’s Superfund Innovative Technology Evaluation (SITE) Program and the Mine Waste Technology Program (MWTP). Two mercury contaminated materials were selected for treatment by three types of stabilization technologies.
The purpose of the study was to determine the effectiveness of the three stabilization technologies for immobilizing mercury in the waste rock materials and therefore reducing leachable mobile mercury in the effluent. Several mercury-bearing materials from the site were considered for testing. A material with high levels of leachable mercury was selected as the primary target of the study, and is referred to as “Mercury Ore”. As a secondary objective, treatment effectiveness was evaluated on material that was lower in mercury concentration, but present in large quantities and is referred to as “Waste Rock”.
Three stabilization technologies were evaluated as part of this study: (1) a Silica Micro Encapsulation (SME) process developed by Klean Earth Environmental Company (KEECO), (2) an inorganic sulfide stabilization technology (ENTHRALL®) developed by E&C Williams, and (3) a generic phosphate treatment.
The primary objective of this study was to determine the effectiveness of the three stabilization technologies (silica encapsulation, phosphate, and sulfide) in reducing the quantity of leachable mercury from SBMM material. Waste material evaluated in this study consisted of “mercury ore” from the south white gate pile and “waste rock” from the north yellow pile. The mercury ore was the primary test material due to its demonstrated ability to produce consistent and detectable levels of leachable mercury. The waste rock was included because it is a common material at the site, even though it yields lower levels of leachable mercury. In order to evaluate the performance of the three technologies, the leachable and mobile mercury (defined as the mercury in the <25µ filtered leachate fraction) from control columns receiving no treatment was compared to the leachable and mobile mercury in the treatment columns. Specifically, the objective was to achieve a 90% reduction in the total mass of mercury leached from each treatment relative to the control over a 12-week continuous column leaching study.
Leachability results from the no treatment control columns revealed that the predominant source of leachable mercury was found in the particulate fraction, i.e. approximately 96%. The phosphate treatment dramatically increased the levels of both the particulate and dissolved fractions (<0.45µm) over the course of the 12-week study. The dramatic rise in leachable mercury brought about by the phosphate treatment invalidates its utility as a remedial alternative for materials at the SBMM site. The E&C William’s ENTHRALL® Technology did not appear to be effective in reducing the levels of mobile mercury in the mercury ore column tests. The total mass of mercury in both the particulate and dissolved fractions are statistically similar to the control. KEECO’s Silica Micro Encapsulation Technology applied both in situ and ex situ, was effective in reducing mobile mercury (<25 µm) very close to the 90% reduction goal of the study. However, there was a significant increase in the mass mercury levels in the dissolved fraction (<0.45µm). The in situ applications exhibited a 198% increase relative to the control, and the ex situ exhibited a 238% increase.
Contact:Ed Bates
bates.edward@epa.gov