Active Activities - Activities IV
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Activity IV, Project 11:
Pit Lake System Characterization
and Remediation for Berkeley PitPhase II
An interdisciplinary team of Montana Tech researchers is currently studying several aspects of the Berkeley Pit Lake system to better understand the system as a whole, which may lead to new or improved remediation technologies to be used during future cleanup. The information obtained from the studies will be used to predict future qualities of the water, to evaluate the natural rate of remediation, to determine if partial in situ remediation may be practical prior to expensive pump and treat remediation, and to predict water quality for similar bodies of water in the United States. The following research is being conducted on the Berkeley Pit lake: Water/Wall Rock Interactions; Bioremediation of the Berkeley Pit Lake System; and Tailings Deposition into the Berkeley Pit.
Organic Carbon in Berkeley Pit Sediments
Late in 1997, the Mine Waste Technology Program funded several projects to chemically and physically characterize the Berkeley Pit Lake water as a function of depth at several positions within the pit. Reports on this work are being prepared for the Berkeley Pit Characterization Project, Mine Waste Technology Program Activity IV, Project 8. The section, Analyzing Organic Substances in the Berkeley Pit Water, has demonstrated that the organic carbon content of the water is approximately 2 to 3 ppm. There appears to be some minor changes in total organic carbon (TOC) concentration as a function of depth in the pit lake.
Considering the sources of water for the pit lake and the similar concentrations of TOC in the in- flow and pit lake waters, it is reasonable to assume that the organic material in the water of the Berkeley Pit Lake is typical of alpine ground and surface waters. Although not yet identified directly, it is also reasonable to assume that a major fraction of the TOC is humic material. Humic substances are well known to be important factors in controlling the chemistry of aquatic ecosystems. Humic material bind hydrogen ions, metal ions, and other organic compounds; adsorb strongly at aqueous/solids interfaces; and participate in the redox and photochemistry of surface waters.
Wall Rock/Water Interactions
To understand the processes of water-rock interaction in the pit environment, we need to know more about the mineralogy of the pit walls and how these minerals interact with rain water, oxidized (shallow) pit water, and reduced (deep) pit water. The main objectives of this project are: 1) to collect a suite of samples from the north high wall of the Berkeley pit, focusing on material that contains abundant secondary minerals (post mining oxidation products); 2) to collect a suite of samples from the walls of the Lexington tunnel (e.g., dripstones forming at acid rock drainage seeps); 3) to characterize the mineralogy of these samples by the scanning electron microscopy/energy dispersive spectrometer and x-ray diffraction; and 4) to interact selected samples with distilled water, oxidized pit water, and reduced pit water to document changes in solution chemistry (e.g., pH, metal concentration) and solid mineralogy with time.
Bioremediation of the Berkeley Pit Lake System
Very little is known about the organisms that are impacted by mine waste in the Berkeley Pit Lake system. It is known that if heterotrophic and autotrophic organisms are properly nutrified, they can bioremediate mine waste-influenced areas as a benefit of their physiological processes.
However, before any type of bioremediation of an ecosystem can begin, it is essential to gain a fundamental understanding of the components of the microbial community. Defining the baseline community structure is the first step toward understanding the interaction of the different biota and toward assessing any improvement in biodiversity within the biotic community. Progress toward this understanding has been made clearer by previous research.
Tailings Deposition into Berkeley Pit
One potential course of action of ongoing Montana Resources operation adjacent to the Berkeley Pit is to deposit tailings into the Berkeley Pit instead of pumping them up to the Yankee Doodle Tailings Pond. As a result, a high pH tailings slurry would be mixed with the low pH Berkeley Pit water. The exact result of tailings deposition into the Berkeley Pit is not clear. This research will focus on three main areas:
- water quality of Berkeley Pit water as tailings are deposited;
- long-term stability of tailings/water mixture; and
- long-term stability of tailings alone.
Organic Carbon in Berkeley Pit Sediments: Total organic carbon concentrations are significantly higher in the sediments than in the water column. The source of the organic carbon must still be determined.
Wall Rock/Water Interactions: Humidity cell tests using wall rock from the Berkeley Pit and distilled water produce effluents very similar to the water currently in the Berkeley Pit in terms of dissolved metals concentrations.
Bioremediation of the Berkeley Pit Lake System: Significant dissolved metal concentrations were observed after algae found in Berkeley Pit water were grown in optimum conditions. This is important information for future in-situ remediation strategies that may be employed at the Berkeley Pit.
Tailings Deposition into Berkeley Pit: Limed tailings, when added to Berkeley Pit water on a 1:1 ratio (volume), significantly raise the pH and lower the dissolved metal concentrations, while backfilling the pit at the same time.
This project was completed, and the final report is being prepared.
Activity IV, Project
An Investigation to Develop a
Technology for Removing Thallium
from Mine Wastewaters
The thallium literature review was conducted as a necessary precursor study under the Mine Waste Pilot Program Activity I Issues Identification and Technology Prioritization Report to determine whether a pilot-scale demonstration of thallium removal should be performed. A similar review for arsenic (Mine Waste Pilot Program Activity I Issues Identification and Technology Prioritization Report: Arsenic) resulted in a very successful pilot scale demonstration of three arsenic removal technologies. Thallium removal technologies are not developed to the same state of the art as the arsenic removal technologies. Therefore, the conclusion is that further laboratory bench-scale test work and development are required before pilot-scale demonstrations are performed by MSE Technology Applications, Inc.
This research is being conducted in response to the need for bench-scale laboratory investigations to develop appropriate thallium removal technologies prior to a pilot-scale demonstration project. The question is, what technologies may be appropriate for removing thallium to levels of 1.7 ppb? Two technologies that may be able to meet the proposed thallium level are proposed for laboratory bench-scale experimental study, e.g., manganese dioxide adsorption (readily available as a waste product from zinc electrowinning operations) and reductive cementation of thallium utilizing elemental iron (a relatively inexpensive reagent available in scrap form).
Preliminary research has begun. The project will be completed in March 2001.
No investigation has been conducted of the reactions occurring in the reduced zone of a tailings heap. Generally, it is believed that any metal oxides that are mobilized in the upper oxidized zone will be reprecipitated as sulfides in the lower reducing zones of the tailings. Numerous metal sulfides exist and may be formed in this reducing zone of the tailings. These complexes may be mobilized as the reduction-oxidation (redox) potential changes within the tailings. In the Berkeley Pit, if tailings are deposited into the Pit lake, and the system's redox potential changes over time, any metal sulfide complexes could be mobilized and enter the deep aquifer surrounding the Pit.
Preliminary work has begun. The project will be completed in March 2001.
This project applies to artificial neural network (ANN) analysis of geochemical and similar data sets, such as those acquired from the Berkeley Pit in Butte, Montana. There are two main types of ANN, supervised and unsupervised networks, and both lend themselves to analyses of this nature. Supervised networks are used in conjunction with or in place of conventional prediction models. They require sets of known inputs and target results or measurements. Unsupervised networks serve a useful function as data mining tools. They do not require pairs of input/target values but instead make an unbiased determination of groups or clusters that occur in the data.
Preliminary work has begun. The project will be completed in March 2001.
This research project will be done in phases. The first task is to conduct a comprehensive literature search of imaging spectroscopy and its application to mining and mine waste. If the technology is found to be viable for characterizing mining-impacted areas, a second phase project may be funded.
Minimal progress was made on this project due to a sabbatical taken by the principle investigator. Work is planned to begin in fiscal 2001.
This research project is designed to study and characterize several aspects of the Berkeley Pit lake system to gain a better understanding of the pit lake systems. The information obtained from the Berkeley Pit lake research will be used to predict future qualities of the water, to evaluate the potential for natural remediation, to determine if partial in-situ remediation may be practical prior to pump and treat remediation, to develop new or improved remediation technologies, and to predict water quality for similar bodies of water in the United States. The following areas of research and testing for the Berkeley Pit lake have been determined: Humic Remediation Potential; Algal Remediation of Berkeley Pit Water; Berkeley Pit Aquifer Modeling; and Remediation by Photocatalysis.
Humic Remediation Potential
Humic substances have widely varying chemical compositions and molecular weights. These substances are generally acidic and are considered to be polymeric in structure. Humic materials are produced by the biological and chemical degradation of plant and animal matter and are often operationally separated into two water-soluble fractions, fulvic acids, and humic acids. The distinction between these two groups is a result of different molecular-weight ranges, solubilities, and the separation procedure used. The fulvic acid group has the lower molecular-weight range and higher water solubility. Chemical analyses of humic materials has consistently demonstrated the presence of a large fraction of aromatic material and carboxylic acid and phenolic functional groups. These oxygenated functional groups are responsible for the strong binding of the humic materials to mineral surfaces and the binding of metal ions in aqueous solutions.
Algal Remediation of Berkeley Pit Water
Ongoing research is beginning to help us understand the microbial ecology of the Berkeley Pit Lake System, with ever increasing information becoming available regarding the diversity of algae, protistans, fungi and bacteria that inhabit this mine waste site. Defining the baseline community structure has been the first step not only toward understanding the interactions of the different groups of organisms but also toward assessing any improvement in biodiversity within the biotic community. Now that this first step has begun, this research will investigate how some of these extremophiles, specifically algae, that have been isolated from the Berkeley Pit Lake System may be used as a potential solution for bioremediation. The primary goal of this study is to determine the potential utilization of algae for bioremediation of the Berkeley Pit Lake System.
Berkeley Pit Aquifer Modeling
The water level in the Berkeley pit has risen a little more than 1 foot per month for the last several years. There are several sources of ground water and a range of ground-water qualities entering the pit: a) contaminated ground water from the underground workings in the bedrock aquifer west of the pit; b) uncontaminated ground water from the bedrock aquifer east and southeast of the pit; and c) contaminated alluvial ground water from east and south of the pit. At a water-depth of 850 feet, the rising water in the pit is presently not in contact with the alluvial aquifer, but rather, seepage faces have formed along the rim of the pit near the bedrock-alluvium contact. The rising water level in the pit will reach a depth of about 1,150 feet (100 feet above the bedrock-alluvial contact) before controls will be implemented.
Presently, a ground-water divide exists roughly coincident with Continental Drive between the Berkeley Pit and the Butte valley. Ground water and surface water north of the divide flow into the pit while ground water and surface water south of the divide flow into the Metro Storm Drain and ultimately into Silver Bow Creek. As the pit water level rises above the bedrock-alluvium contact, the ground-water gradient toward the pit will decrease, possibly shifting the ground-water divide south of the pit, thereby, diverting a portion of the ground water now flowing into the pit to the Butte valley. This would manifest itself as an increase in water levels throughout the residential area south of the pit and a flow increase in the metro storm drain.
Remediation by Photocatalysis
Numerous technologies are available for remediating acid rock drainage. These technologies include biosorption, mineral/resin adsorption, chemical precipitation, ion exchange, freeze crystallization, evaporation, and a host of others. Several of these technologies have been tested over the past decade on Berkeley Pit Lake water. Lime precipitation became recognized as the U.S. Environmental Protection Agency's Best-Determined Available Technology for remediating the Berkeley Pit water. However, the conventional process had to be modified to meet discharge standards regarding pH and manganese and aluminum concentrations. The resulting two-stage process required an intermediate filtration step to remove precipitates that would redissolve upon continued lime addition.
In a previous study funded by the Mine Waste Technology Program, a process was developed for remediating Berkeley Pit water while simultaneously recovering the copper and zinc and producing other marketable products. This process uses a combination of the technologies listed above but has a novel approach for using ultraviolet radiation to meet the objectives. As indicated, the process uses five stages to selectively remove various metal constituents in the water by precipitation. Solid/liquid separations between the individual stages allows for the precipitates to be recovered and eventually marketed. Furthermore, the process also meets the discharge requirements of the metals including that of arsenic.
Preliminary work has begun. The project will be completed in March 2001.
All figures and tables can be found in the Mine Waste Technology Annual Report. (PDF, 5.5 M, 74 pp)