Active Activities - Activity III
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Activity III, Project 3:
Sulfate-Reducing Bacteria Demonstration
Acid generation typically accompanies sulfide-related mining activities and is a widespread problem. Acid is produced chemically, through pyritic mineral oxidation, and biologically, through bacterial metabolism. This project focuses on a source-control technology that has the potential to significantly retard or prevent acid generation at affected mining sites. Biological sulfate reduction is being demonstrated at an abandoned hard-rock mine site where acid production is occurring with associated metal mobility.
For aqueous waste, this biological process is generally limited to the reduction of dissolved sulfate to hydrogen sulfide and the concomitant oxidation of organic nutrients to bicarbonate. The particular group of bacteria chosen for this demonstration, sulfate-reducing bacteria (SRB), require a reducing environment and cannot tolerate aerobic conditions for extended periods. These bacteria require a simple organic nutrient.
This technology has the potential to reduce the contamination of aqueous waste in three ways. First, dissolved sulfate is reduced to hydrogen sulfide through metabolic action by the SRB. Next, the hydrogen sulfide reacts with dissolved metals forming insoluble metal sulfides. Finally, the bacterial metabolism of the organic substrate produces bicarbonate, increasing the pH of the solution and limiting further metal dissolution.
At the acid-generating mine site chosen for the technology demonstration, the Lilly/Orphan Boy Mine near Elliston, Montana, the aqueous waste contained in the shaft is being treated by using the mine as an in situ reactor. An organic nutrient was added to promote growth of the organisms. This technology will also act as a source control by slowing or reversing acid production. Biological sulfate reduction is an anaerobic process that will reduce the quantity of dissolved oxygen in the mine water and increase the pH, thereby, slowing or stopping acid production.
The shaft of the Lilly/Orphan Boy Mine was developed to a depth of 250 feet and is flooded to the 74-foot level. Acid mine water historically discharged from the portal associated with this level.
Pilot-scale work at the MSE Technology Applications, Inc., Testing Facility in Butte was performed in fiscal 1994 prior to the field demonstration. The objective of these tests was to determine how well bacterial sulfate reduction lowers the concentration of metals in mine water at the shaft temperature (8 degrees C) and pH (3).
During fiscal 2000, the field demonstration was again monitored on a regular basis. Figure 2 presents a cross-section of the mine and technology installation.
During the past year of monitoring, the data generally demonstrated a decrease in metals concentrations (see Figure 3), with the exception of manganese, which SRBs do not effectively remove. An increase in metals was observed during spring runoff as occurred in prior years; however, the levels decreased when flow rates returned to normal. Field demonstration monitoring has been ongoing for 6 ½ years. Monitoring is scheduled to be completed in June 2001.
A significant environmental problem at abandoned underground mines occurs when the influx of water contacts sulfide ores and forms acid and metal-laden mine discharge. The Underground Mine Source Control Project demonstrated that grout materials can be used to reduce and/or eliminate the influx of water into the underground mine system by forming an impervious barrier that results in reduced, long-term environmental impacts of the abandoned mine.
Ground water flow is the movement of water through fractures, fissures, or intergranular spaces in the earth. Some of the fractures are naturally occurring, others were the result of blasting during mining.
For this demonstration, a closed-cell, expandable polyurethane grout was injected into the fracture system that intercepts the underground mine workings. The demonstration consists of three phases: 1) extensive site characterization; 2) source control material identification and testing; and 3) source control material emplacement.
Phase One, completed in 1999, consisted of characterization studies, including hydrogeological,geological, geochemical, and geophysical information gathering directly related to the mine and its operational history.
Phase Two encompassed source control material testing. Approximately 40 materials were tested according to ASTM methods for acid resistiveness, shear strength, plasticity, compressive strength, compatibility, and viscosity. The source control grout material selected for injection was Hydro Active Combi Grout, a closed-celled, expandable polyurethane grout manufactured by de neef Construction Chemicals, Inc. When compared to a cement-based source control material, this material offered the following advantages: greater retention of plasticity; less deterioration due to the acidic conditions and during rock movement; and better rheological characteristics.
The Miller Mine near Townsend, Montana, was selected for the demonstration because the underground workings were accessible, it has a point-source discharge into the underground workings, the slightly acidic inflow is laden with heavy metals, and the inflow could be potentially controlled using the source control technology.
Phases One and Two were completed in March 1999. Phase Three, the field emplacement (shown in Figure 4), was completed in October 1999.
First year monitoring results indicate that the water flow into the underground mine was reduced from 10 to 15 gpm to approximately 1 to 1.2 gpm as a result of Phase III field emplacement.
Surface waste piles from mining operations were historically placed in drainage basins in front of the haulage tunnel. Surface water in the drainage, discharge from the mine, and precipitation usually contacted the waste pile. The water came in contact with the sulfide ore in the pile and infiltrated through the pile, where acid formed and the water became metal-laden. This water percolated from the toe of the pile and flowed into the closest surface water. The objective of this Mine Waste Technology Program demonstration was to provide source control technologies that could be applied in situ, meaning that the pile is stabilized in place and not excavated and moved to another location for stabilization. By using strategically applied in situ source control technologies, there will be a decrease in water infiltrating through the pile and ground water contact with surface waste pile material, thereby, decreasing the environmental impact.
Surface waste piles from historical mining activity, in many cases, consist of broken, low-grade, sulfide ores. When water and oxygen contact the sulfide ores, acid is formed, resulting in increased levels of dissolved metals in the water associated with the pile. The source of the water infiltrating the pile is usually precipitation onto the pile and/or from surface water (i.e., discharge water from a mine adit, stream flow, or in some instances ponded stream/discharge water). When the water discharges from the surface waste pile, it is acidic and metal-laden causing a significant environmental problem.
Usually in such situations, the surface waste pile is excavated and placed in a designed repository. However, this can be expensive, and in some instances, excavation of the pile or construction of a repository is not feasible. In certain instances, in situ application of source control technologies at a surface waste pile is the optimal solution. The source control technologies are strategically placed into the surface waste pile such that the infiltration of surface water and ground water flow through the pile are eliminated or reduced, resulting in a reduction of acidic, metal-laden water.
The demonstration consists of three phases: 1) site characterization; 2) source control materials testing; and 3) field emplacement.
Phase One, site characterization, included geochemical, geological, hydrogeological, and mineralogical studies that provided information directly related to the surface waste pile, the mine, the regional water system, and past operational procedures.
Phase Two, source control materials testing, was performed to determine if select source control material were acid resistant, was affected by wet/dry or freeze/thaw cycling, and if it would be impervious once it was emplaced onto the surface waste pile. The physical characteristics of the surface waste pile material were also defined in the bench-scale laboratory setting.
The project site for this demonstration is the Peerless Mining Property located south of Rimini, Montana. The site was selected because of its size, hydraulic characteristics, and its water quality (see Figure 5). A major factor in the selection of the site was that it had an acidic, metal-laden, point-source discharge flowing from the toe of the surface waste pile, and the upgradient water sources were of better quality and near neutral pH.
Phases One and Two were finalized by March 26, 1999. Phase Three, field emplacement, was initiated in September 1999 and finalized in November 1999. At the Peerless Mine, both surface water and ground water contacted the surface waste pile material and contributed to the acid mine drainage formation. Figure 6 shows the French drain system constructed to hydraulically control the ground water flow at the site.
The French drain was placed upgradient of the surface waste pile allowing the ground water to be transported away from the acid forming material. Figure 7 shows a spray-applied cover being applied to reduce the infiltration of precipitation through the pile. The spray-applied cover material used at the site (see Figure 8) was a flexible, urethane grout called KOBAthane 4990, manufactured by General Polymers, Inc.
Long-term monitoring results indicate that the water quality of the seep flowing from the toe of the surface waste pile was improved. After the technology emplacement, the dissolved metal concentrations for zinc, cadmium, and copper were below the National Drinking Water Maximum Contaminant Standards.
Final Report - Surface Waste Piles Source Control Demonstration Project (PDF, 16 M, 55 pp)
Thousands of abandoned mine sites in the western United States impact the environment by discharging acid mine drainage (AMD) to surface water or ground water. Acid mine drainage is formed when sulfide-bearing minerals, particularly pyrite, produce oxygen and water in a chemical reaction that results in an increased acidity of the water (lowered pH), and increased concentration of dissolved metals and sulfate.
At many abandoned mine sites in the West, conventional treatment strategies for AMD (e.g., lime neutralization) are not feasible because of the remoteness of the mine locations, insomuch as a lack of a power source and limited site accessibility in winter. Sulphate-reducing bacteria (SRB) are capable of reducing the sulfate to sulfide, decreasing the load of dissolved metals in the effluent by precipitating metals as sulfides, and increasing the pH of the effluent. To demonstrate the feasibility of using SRB passive technology for mitigation of AMD emanating from the toe of a waste rock pile, three bioreactors were built at the abandoned Calliope Mine site located near Butte, Montana.
The Calliope mine site includes a collapsed adit discharging water into a large (66,000 cubic yards) waste rock pile. This relatively good quality water flows over the top of the waste rock and accumulates in a small lower pond at the toe of the pile. The AMD is mostly produced by atmospheric water that infiltrates the waste rock pile and reappears on the surface at the toe of the pile enriched in metals and with a pH of 2.6. This AMD also flows to the pond where it mixes with good quality water and lowers its pH. A portion of the water that accumulates in the pond has been diverted for treatment to three engineered bioreactors that were built at the site to demonstrate the SRB technology.
The SRB bioreactors constructed at the Calliope abandoned mine site in the fall of 1998 are approximately 70 feet long, 14 feet wide, and 6 feet high. They are placed in parallel (see Figure 9) downstream from the pond, allowing the AMD to be piped to and treated in the reactors using gravity flow. The bioreactors are designed to evaluate the SRB technology applied under different environmental conditions.
Two bioreactors are placed in trenches. One is constructed above the ground using a 12-foot-wide metal half-culvert to investigate the impact of seasonal freezing and thawing on SRB activity. To evaluate the efficiency of the SRB at optimal pH and oxidation-reduction potential (EH), two of the reactors contain a passive pretreatment section to increase the alkalinity of the AMD.
Each reactor is filled with a combination of organic carbon and cobbles placed in discrete chambers (see Figures 9 and 10). Reactors II and IV also have a crushed limestone chamber. Each of these media is expected to play a certain role in the treatment train. 1) Organic carbon is the bacterial food supply, and because it was provided in the form of cow manure, also the SRB source. 2) For the pretreatment section, a chamber with cow manure was included to lower the EH of AMD. 3) Crushed limestone provided the buffering capacity to increase the pH of AMD in the pretreatment section. 4) Cobbles placed in the reactive, primary treatment section of the bioreactor constitute stable substrate for bacterial growth.
Chambers filled with organic carbon or limestone are each 5 feet long, whereas, chambers filled with cobbles are 50 feet long. Such dimensions were selected based on the literature review and information acquired through the bench-scale test that was conducted in the MSE Technology Applications, Inc., laboratory in 1998. Preliminary results of the bench-scale test, at the time of the bioreactor's design, indicated the required residence time in the reactors should range from 3 to 5 days. This resulted in the bioreactors being sized for a flow rate of one gallon per minute. To provide flexibility, the flow and hydraulic head control systems placed in the bioreactors ensure a much wider range of the residence time.
The main challenges were to design the organic carbon chambers so the AMD would permeate through the entire cross-sectional area without channeling and to ensure that the organic substrate did not settle. These goals were achieved by placing the organic substrate in the cellular containment system consisting of 10 lifts of TerracellTM (see geogrid in Figure 10) that would limit settling of the organic matter to each individual cell if it occurred. The TerracellTM lifts were positioned at 600 degrees off the horizontal plane to facilitate packing with the organic substrate and to promote migration of AMD along a wavy-shaped flowline.
Reactor construction was completed in November 1998, and the reactors have been in operation since December 1998. The operation plan stipulated that the two below-grade reactors (II and III) would flow at the rate of 1 gallon per minute (gpm) and reactor IV would be shut down for the winter to let it freeze full of AMD. After spring thawing, the flow rate of reactor IV would also be 1 gpm. The 1-gpm flow rate allows for approximately a 5½-day residence time of AMD in reactors II and IV and a 4½-day residence time in reactor III. The residence time of the AMD in a single organic carbon chamber was approximately 10 hours for the flow rate of 1 gpm.
Flow through Reactors III and IV has been maintained as desired for most of the time. The flow rate through Reactor II, however, started to decrease in May 1999 and ceased at the beginning of June. The flow rate was restored in July after the upgradient cell with organic carbon was chemically treated to remove biofouling and associated plugging. Similar behavior of Reactor II was observed again in May 2000. This time, the permeability of the upgradient chamber was increased using an appropriate physical treatment. The repetitive plugging events of the most upgradient chamber in Reactor II seems to be attributed to a tighter packing of organic carbon in this chamber in comparison to other chambers.
The performance of each reactor has been monitored by monthly sampling of the influent (AMD) and effluent, and continuous monitoring of selected parameters using appropriate sensors and data loggers. Water samples have been analyzed for sulfate; alkalinity; SRB count; heterotrophic bacteria count; dissolved oxygen; EH; and metals that include aluminum, zinc, cadmium, copper, iron, manganese, and cadmium. Temperature, water level, and flow rate were recorded at 4-hour intervals by two data loggers. Selected results of the reactors performance are shown in Figures 11 through 14.
The first 8 months of operation can be described as a period in which the microbial populations were becoming established within the reactors. It should be noted that the reactors were started in the winter when temperatures were not ideal for microbial growth. As the reactor temperatures began to increase in April 1999, an increase in SRB populations (Figure 11) was also seen. During the second winter of operation, the well-established SRB population was not affected by the low temperatures.
Much of the metals removal observed during the first 7 months of operation can be attributed to adsorption. Once sorption sites fill and SRB populations become established, many metals, like zinc and copper [(Figures 12 and 13 (logarithmic scale)] and cadmium (Figure 14), were removed from the AMD to threshold levels that were approximately 500 micrograms per liter (µg/L) to 800 µg/L for zinc, 80 µg/L for copper, and 5 µg/L for cadmium. These removal levels were achieved despite the relatively low metals-concentrations in the influent AMD, caused by low atmospheric precipitation during the last 14 months of operation. For the metal concentrations present in the AMD at the Calliope site, the SRB population above 103 in one milliliter of the treated water was sufficiently high to maintain these removal levels. This means that the higher SRB population had no direct affect on the metal removal levels. This project will continue through the end of 2001.
Final Report: Sulfate - Reducing Bacteria Reactive Wall Demonstration (PDF, 1.8 M, 55 pp)
The technology addressed in this project is designed to poll and warehouse remote sampling data from the Calliope Mine site automatically. The remote monitoring is linked to the MSE Technology Application, Inc. (MSE) Testing Facility in Butte, Montana, via a cellular modem connection. Data from the remote site is polled by a dedicated personal computer (PC) located at the MSE Testing Facility. The project also includes technology to demonstrate remote site monitoring using two web cameras. The cameras download images to the PC at the MSE Testing Facility. The images and data can be viewed via the Internet from the dedicated PC.
The polling PC at the MSE site runs software designed for data loggers at the mine site. This software has the capability to poll data from the data loggers on a regular basis. Data is retrieved from the mine site only once a day since this is a solar-powered operation and more frequent retrieval would require a large battery bank. Once data has been retrieved, it is then transferred to an industrial database for warehousing. The polling PC is also connected to the World Wide Web via a dedicated 56-Kbs frame relay (see Figure 15).
Once data is stored it can be accessed from anywhere or any PC that has Internet capability. An Internet service provider was obtained to allow the connection as well as provide ample Internet protocol addresses and domain names for the web site. The web site domain name for this project is http://www.environment-watch.com. Figure 16 shows the web site home page.
The Web screens were designed to allow anyone with a PC and Internet access to view information from the telemetry system. The displays allow viewing of historical data as well as trending of data (see Figure 17).
Two remote cameras are connected to a small on site camera web server. The server is connected to the remote cellular modem just like the data loggers. The polling PC makes three calls to the mine site daily:
- one call in the morning to download site camera images of that morning;
- one call in the morning to retrieve data from the data loggers; and one call in the afternoon to download camera images of the site in the afternoon.
Once the data and the photos are downloaded, data is warehoused, and pictures are transferred to the web site for Internet viewing (see Figure 18).
This project also included the task of upgrading the existing data logger's battery storage capacity. The existing In-Situ Hermit 3000 Data Loggers did not have sufficient battery storage to run data loggers and existing instruments at specific sample rates. This problem was solved with the design of a new solar-powered battery charging system. The solar- charged batteries now power data loggers, instruments, the cellular telephone modem, web cameras, and web camera server.
This project installation has allowed additional capacity for future Mine Waste Technology Program projects. These projects can also benefit by using the same web server to post information onto the World Wide Web.
As of September 30, 2000, the project was 100% installed and online. The project will remain open for maintenance and utility costs of the web server and other equipment. Maintenance is required for keeping the web server up to date as well as cover monthly cell phone and Internet service provider charges. This project will be closed out once the Calliope Mine site testing is completed. Possibly, another Mine Waste Technology Program project could pick up the monthly costs in the future.
The technology addressed in this project is designed to reduce or eliminate acid drainage from underground mine workings. The demonstration is intended to illustrate the feasibility of using an innovative source control technology in a way that provides increased stability, structural applicability and continuity, and economical comparability to the conventional methods of acid drainage treatment used by the mining and waste industries. The technology used for this demonstration will be stable in the environment.
The technology selected for this demonstration is a combination hydrostatic bulkhead constructed of concrete and rebar with a colony of sulfate-reducing bacteria (SRB) placed behind the bulkhead. The acid drainage in the mine will be treated by raising the pH of the contained water behind the bulkhead causing metals to be removed. The metals removal processes that can occur include adsorption and complexion of metals by organic substrates, biological sulfate reduction followed by precipitation of metals as sulfides, precipitation of ferric and manganese oxides, adsorption, adsorption of metals by ferric and manganese hydroxides, and filtration of suspended and colloidal materials. Biological sulfate reduction, however, should be the predominant metal removal mechanism.
Preliminary design work was completed for installing a SRB colony behind a bulkhead to be constructed by the American Smelting and Refining Company at the Triumph Mine in Triumph, Idaho. U.S. Environmental Protection Agency (EPA) and MSE Technology Applications, Inc. (MSE) personnel reviewed the preliminary SRB design and agreed that this site was not a viable candidate for installing a SRB colony due to the presence of extensive mine workings that would negate adequate treatment of waters inside the mine.
After eliminating the Triumph Mine as a demonstration site, the search was resumed for another site. It was decided by both EPA and MSE to suspend funding for this project effective fiscal 2001 after additional searching did not locate an appropriate site for this technology demonstration.
Acidic, metal-laden waters draining from abandoned mines have a significant environmental impact on surface and groundwater throughout the nation and the world. Specifically, the State of Montana has identified more than 20,000 abandoned mine sites, on both public and private lands, resulting in more than 1,300 miles of streams experiencing pollution problems.
Acid mine drainage arises from tailings and waste rock containing sulfide minerals and lacking acid-consuming carbonate minerals. Sulfide minerals, such as pyrite (FeS2), are oxidized to form sulfate when water containing oxygen infiltrates tailings and waste rock. This process can be described by the following reaction:
4FeS2 + 15O2 + 2H2O 4FE3 + 8SO42- + 4H+.(1)
The activity of bacteria, such as Thiobacillus ferrooxidans, which are capable of oxidizing inorganic sulfur compounds, greatly accelerates this reaction. The ferric iron (Fe3+) produced in the above reaction also contributes to pyrite oxidation:
FeS2 + 14Fe3+ + 8H2O 15Fe2+ + 2SO42- + 4H+. (2)
T. ferrooxidans is also capable of oxidizing ferrous iron (Fe2+) produced in the above reaction:
4Fe2+ + O2 + 4H+ 4FE3 + 2H2O. (3)
Although the above reaction consumes some acidity, the ferric iron produced is capable of oxidizing more pyrite and producing much more acidity (via reaction 2).
The key to breaking this cycle is preventing the initial oxidation of pyrite. Bound with iron, the sulfur in pyrite is unable to participate in the microbially catalyzed reactions that cause acid generation. Preventing oxygen infiltration into tailings and waste rock is necessary to prevent oxidation of pyrite and subsequent acid generation. An innovative method to prevent oxygen transport into tailings is constructing and maintaining a biologically active barrier on the surface of the tailings. This barrier is made up of microorganisms that consume dissolved oxygen from the infiltrating water, thereby, maintaining the reducing conditions necessary for pyrite to remain bound in mineral form.
MSE Technology Applications, Inc. and researchers at the Center for Biofilm Engineering at Montana State University are investigating the microbial processes involved with establishing and maintaining subsurface and near surface microbial barriers for hydraulic control and microbially catalyzed reactions. Biofilm barrier technology has been successfully tested in laboratory and field-scale systems where permeability reductions of five orders of magnitude were achieved. During these tests, it was also shown that biofilm barriers can successfully remove oxygen from infiltrating waters to trace levels.
By conducting this demonstration, the Mine Waste Technology Program is illustrating the ability of microbial biomass to reduce the permeability of mine tailings and remove oxygen from infiltrating water, thereby, reducing the generation of acid mine drainage. This technology promises to be a cost-effective approach for stabilizing and remediating acid-generating abandoned mine tailings.
A biologically active zone is established in the tailings by adding a nutrient solution to the surface of the tailings pile. The nutrient solution contains low cost ingredients that serve as sources of carbon and energy for microbial growth, as well as sources of nitrogen, phosphorous, and necessary micronutrients. The nutrient solution is formulated to stimulate indigenous oxygen-consuming microorganisms, as well as sulfate-reducing bacteria (SRB). In some cases, a microbial inoculum containing appropriate microorganisms may have to be added. The oxidation of carbon compounds in the nutrient mixture by microorganisms depletes oxygen from infiltrating water. Also, bacterial cells and associated extra-cellular polymers occupy free pore space within the tailings matrix, greatly reducing permeability. The reduction of water volume flowing through the tailings and depletion of oxygen as water passes through the barrier will mitigate pyrite oxidation and subsequent acid generation. The anaerobic conditions and production of organic acids by fermentative bacteria will also promote SRB growth. The SRB activity is desirable because it neutralizes acid and stabilizes metals by H2S-mediated metal sulfide precipitation. After establishing the biological barrier, periodic nutrient treatments are applied to maintain the barrier.
The Mammoth tailings site in the South Boulder Mining District, approximately 18 miles from Cardwell, Montana, was selected for implementing this technology. Two, lined test cells were constructed at the field site in the fall of 1999. An initial nutrient treatment was applied to one of the test cells (treated cell) in the fall of 1999. Additional nutrient treatments were applied to the treatment cell in May, June, and August 2000. The nutrient formulation included molasses as a carbon and energy source, urea as a source of nitrogen, and potassium phosphate. The control (untreated) cell received an equivalent amount of water to that applied to the treatment cell during nutrient treatments. Other than the four nutrient or water treatments, all water entering the test cells was due to natural precipitation. The test cells were not operated during the winter months when they were frozen.
Drainage from the treatment cell had a slightly higher pH and slightly lower oxidation reduction potential than the control cell. The mean pH of drainage from the test and control cells were 6.4 and 6.2, respectively. Microbiological analysis indicated higher populations of total bacteria, general heterotrophic bacteria, and sulfate-reducing bacteria in drainage from the treated cell, relative to the control cell. Populations of sulfur-oxidizing bacteria (e.g., Thiobacillus ferrooxidans) were similar in drainage from both test cells. Dissolved sulfate concentrations were lower in drainage from the treated cell, while total organic carbon concentrations were higher. Drainage from the treated cell had lower concentrations of dissolved aluminum, copper, and zinc and higher concentrations of iron and manganese than the control cell. Overall, these results indicate that treatment with a carbohydrate- (molasses) based nutrient formulation had a mild effect on the biological and chemical processes occurring in the tailings and led to a slight improvement in the water quality of drainage from the tailings. Laboratory column tests (described below) have indicated that protein- (whey) based nutrient formulation was more effective than the carbohydrate-based treatment for mitigating acid mine drainage. During the 2001 field season, a protein- (whey) based nutrient formulation will be applied to the treatment cell.
Laboratory experiments performed at the Center for Biofilm Engineering at Montana State University have included packed-column tests using tailings from the Mammoth Field Site, Crescent Mine (Montana), and the Fox Lake Mine (Manitoba, Canada). The columns packed with tailings from the Crescent Mine failed to generate acidity or significant concentrations of dissolved metals. Treatment of these columns with the carbohydrate-based nutrient treatment did result in a significant decrease in oxidation-reduction potential (ORP) relative to a control column. Three columns were packed with tailings from the Fox Lake site, and two of these received the carbohydrate-based nutrient treatment, while the third column served as an untreated control. One of the treated columns responded with a significant increase in pH and reduction in ORP, as well a decrease in dissolved aluminum and zinc concentrations. However, the other treated column responded with a decrease in pH and an increase in ORP. It is hypothesized that the carbohydrate-based nutrient treatment to this column resulted in the proliferation of acid-generating fungi. This hypothesis is being investigated further at the Center for Biofilm Engineering. Due to the lack of consistent laboratory results and marginal field success with the carbohydrate-based nutrient formulation, a protein-based nutrient formulation using whey (a by-product of cheese manufacturing) was applied to columns packed with tailings from the mammoth site. The whey treatments resulted in a significant increase in the pH and a decrease in the ORP of drainage from the tailings (see Figure 19). This effect was more dramatic and longer lasting than the molasses treatments performed previously. The use of whey-based nutrient treatments is currently being further evaluated in the laboratory.
Overall, results of laboratory and field testing indicate that biological cover technology is feasible for source control of acid mine drainage. However, the results suggest that correct nutrient formulation is critical to the success of the treatment; and in some cases, adding an inappropriate nutrient formulation can decrease the water quality of drainage from mine tailings. Further research is necessary to define the critical parameters for formulating a nutrient mixture for treating a specific mine site.
Processing metallic ores to extract the valuable minerals leaves remnant material behind called tailings. In the case of sulfide mineral-bearing ores, process tailings often contain large quantities of sulfide minerals that do not meet the economic criteria for extraction. These remnant sulfide minerals are usually pyrites and nonextracted ore minerals. The exposure of these minerals to air and water often leads to detrimental environmental conditions such as increased sedimentation in surface waters due to runoff events, increased wind borne particulate transport, generation of acid mine drainage, and increased metals loading in surface and ground waters.
The objective of this demonstration was to identify potential source control materials and apply one or more of them at a selected site. The demonstration consists of two phases: 1) site characterization and materials testing; and 2) materials emplacement and long-term monitoring and evaluation.
Phase one consisted of the site characterization studies, including hydrogeological, geological, and geochemical information directly related to the tailings impoundment. The materials testing and development involved testing, evaluation, and formulation of source control materials for application at the selected site.
Phase two will encompass the application of one or more of the selected
source control materials at the
demonstration site and an evaluation of the material
application and feasibility. Long-term evaluation of the materials will be performed using air borne particulate tests, moisture profiles generated from monitoring equipment, and post-application material tests.
For Phase one, the project site selected for this demonstration is the Mammoth Tailings site located adjacent to the historic mining town of Mammoth, Montana (see Figure 20). Material testing was finalized during the first quarter of 2000. Three source control materials are scheduled to be applied at the Mammoth Tailing site, which include two, polymeric cementitious grouts that incorporate the tailings material as a filler material and a spray-applied, modified chemical grout. Due to forest fire restrictions, the emplacement of the source control materials was postponed from 2000 to the summer of 2001. The project will be completed by the end of calendar year 2001.
The objective of this project is to develop technical information on the ability of an integrated passive biological reactor to treat and improve water quality at a remote mine site. This technology offers advantages over many acid mine drainage (AMD) treatment systems because it does not require a power source or frequent operator attention. For this demonstration, the technology will treat the acidic aqueous waste by removing toxic, dissolved metallic and anionic constituents from the water in situ and increasing the pH so the effluent is near neutral.
The technology uses a series of biological processes for the complete mitigation of AMD by concentrating and immobilizing metals within the reactors and raising the pH of the water. Both anaerobic and aerobic bacteria will be used. The bacteria will be fed inexpensive waste products such as feed-lot wastes. The anaerobic bacteria, sulfate-reducing bacteria (SRB), are a group of common bacteria that are able to neutralize AMD and remove toxic metals. When supplied with sulfate (present in mine water) and a carbon source, SRB produce bicarbonate and hydrogen sulfide gas. Bicarbonate neutralizes AMD while hydrogen sulfide gas reacts with metal ions to precipitate them as insoluble metal sulfides. Aerobic bacteria will be used to mitigate metals, such as iron and manganese, that are not removed satisfactorily by SRB. The result will be an integrated biological system capable of completely and passively mitigating AMD. The field system is depicted in Figure 21.
The first phase of the project will include field site selection and characterization and laboratory testing. Laboratory testing will be performed to identify design parameters for the field design.
The second phase of the project will include the design and construction of an integrated passive biological treatment system to treat AMD at the selected remote mine site, the Sure Thing Mine located in Southwest Montana.
The design of the field-scale system was completed in fiscal 2000. Construction was scheduled during the summer of 2000 but was postponed because wild fires caused National Forest closures. Construction is now scheduled for the summer of 2001.
This demonstration project is being conducted in conjunction with the U.S. Environmental Protection Agency's Superfund Innovative Technology Evaluation Demonstration Program. Mercury contamination often is a critical problem at mine sites, and there is a recognized need to identify technologies for mercury remediation. The application of an in situ mercury stabilization technology would provide an alternative treatment to completely removing mercury-contaminated materials from remote abandoned mine sites. As part of the overall project, MSE Technology Applications, Inc. (MSE) is responsible for conducting technology assessment activities to comparative mercury stabilization tests using mercury-contaminated material.
The Sulphur Bank Mine in Clear Lake, California, was chosen as the source of mercury contaminated mining wastes for this demonstration project. This abandoned mine, located in a geothermal active area, was historically mined for mercury and sulfur. It is now part of a 120-acre superfund site containing tailings, rock piles, and a pit lake. The mine tailings are located upgradient and extend into and along the shoreline of Clear Lake. The development of an in situ mercury treatment/stabilization technology could be used to address the significant mercury contamination problems at the site.
The main objective of this effort is to determine a suitable method for in situ mercury stabilization. This technology demonstration project will help to show the effectiveness of various technologies for the in situ treatment/stabilization of mercury contaminated mining materials. Several applicable technologies will be identified and tested. These may include chemical precipitation, micro-encapsulation, and grouting.
MSE is conducting a series of comparative column treatability tests of various mercury treatment/stabilization technologies. The technologies were selected with regards to their ability to reduce the leaching, mobility, and toxicity of mercury contamination. Two materials from the Sulphur Bank Mine site have been selected for testing. The effectiveness of the treatment technologies will be evaluated by preforming post-treatment kinetic column leach tests. The immobilization of mercury over time and the reduction of leachable mercury relative to untreated controls will be determined. The information gained from this project will serve to provide data for abandoned mine remediation projects.
The purpose of the Selenium Removal/Treatment Alternatives Demonstration Project is to: 1) evaluate the performance of the selected processes in the field using selenium-bearing water; 2) evaluate the affect of competing ions on selenium removal efficiency; and 3) determine full-scale capital and operating costs of the processes being demonstrated.
The following selenium removal technologies have been demonstrated at field-scale: 1) U.S. Environmental Protection Agency's (EPA) Best Demonstrated Available Technology (BDAT) for treating selenium-bearing waters and coprecipitation of selenium using ferrihydrite as optimized by MSE Technology Applications, Inc. (MSE); 2) catalyzed cementation technology developed by MSE; and 3) biological reduction of selenium technology developed by Applied Biosciences Corporation of Park City, Utah. An enzymatic reduction of selenium technology also developed by Applied Biosciences Corporation of Park City, Utah, was demonstrated on a bench-scale.
The field demonstrations were conducted at Kennecott Utah Copper Corporation. The influent water used for the demonstration was a ground water containing approximately 2 ppm selenium. The primary objective was to reduce the concentration of dissolved selenium in the effluent waters to a level under the National Primary Drinking Water Regulation Limit for selenium of 50 ppb established by EPA.
Ferrihydrite precipitation with concurrent adsorption of selenium onto the ferrihydrite surface is the BDAT for treating selenium-bearing waters. For the coprecipitation to occur, ferric ion (Fe+3) must be present in the water. Selenate (Se+6) is removed from the water at pH below 4. The chemical reaction for ferrihydrite precipitation of selenium is:
Se+6 + Fe(OH)3(5) + 4H2O Fe(OH)3(5) + SeO4-2 + 8H+
The ferrihydrite precipitation process is shown in Figure 22.
Catalyzed Cementation of Selenium
Catalyzed cementation has been developed to remove arsenic and other heavy metals such as thallium and selenium from water. The term catalyzed cementation describes the process's ability to remove contaminants from solution by cementation (adsorption) onto the iron surface. It is anticipated that the catalyzed cementation process will have the ability to treat and remove selenium from solution regardless of its valence state (+6 or +4). To optimize the cementation process, proprietary catalysts are added to increase the removal efficiency of the process. This process has been shown in similar tests to reduce selenium concentrations below the Maximum Contaminant Level of 50 ppb. The catalyzed cementation process is shown in Figure 23.
Biological Reduction of Selenium
To accomplish biological selenium reduction, researchers at Applied Biosciences of Salt Lake City, Utah, have developed a process using baffled anaerobic solids bed reactors (BASBR). The process is depicted in Figure 24. Selenium (selenate and selenite) will be reduced to elemental selenium by specially developed biofilms containing specific proprietary microorganisms. This produces a fine precipitate of elemental selenium. The marketability of the elemental selenium product will be investigated during this project. This process is being demonstrated using equipment designed and constructed by ABC with assistance from Kennecott Utah Copper Corporation.
The pilot-scale BASBR will be used to investigate the feasibility of using a defined mixture of Pseudomonas and other microbes for removing selenium from influent water.
Enzymatic Reduction of Selenium
Applied Biosciences also demonstrated, at bench scale, a proprietary enzyme technology for selenium removal. This metal reducing technology is based on proprietary enzyme extraction/purification methods combined with unique immobilization/encapsulation techniques that keep the selenium reducing enzyme(s) in a functional arrangement within an immobilized/encapsulated matrix. The adaptation, enhancement, and use of microbial components, and byproducts (proteins, enzymes, and polymers) show considerable promise for treatment/removal of metals and other inorganics in complex wastewaters. Normal biofilms developed for selenium reduction and removal can be quickly overgrown as the bioreactor system is exposed to waste and process waters containing indigenous microbes and nutrients. Overgrowth of the selenium-reducing population in a bioreactor can be delayed by optimizing the bioreactor and nutrient selection for the chosen selenium reducer. However, once nutrients are added, time and indigenous microbes slowly erode the selenium reducing capability. This situation can be avoided by using selenium-reducing enzyme preparations.
The field demonstration of the BDAT technology, catalyzed cementation, and biological reduction technology was completed. All three technologies removed selenium to below the project objective of 50 ppb under optimum conditions. The biological reduction technology was the most consistent process tested, with the majority of results less than the detection limit for selenium of 2 ppb. An interim report is being drafted and will be submitted to EPA for review in November 2000.
The laboratory demonstration of the enzymatic selenium reduction technology was completed. Although selenium reducing enzymes were isolated, the unstable nature of them prevented a pilot-scale demonstration of this technology. Applied Biosciences is preparing a report about the laboratory study that will be included in the final project report. The final report will be submitted to EPA for review in April 2001. Project closeout is scheduled for June 2001.
Final Report (PDF, 4.75 M, 133 pp)
The objective of this project is to develop integrated, optimized treatment systems for processing Berkeley Pit water. The Berkeley Pit is an inactive open-pit copper mine located in Butte, Montana. Currently containing approximately 30 billion gallons of acidic, metals-laden water, the Berkeley Pit is filling at a rate of approximately 3 million gallons per day and is a good example of acid rock drainage.
Two optimized flow sheets will be developed for this project. One flow sheet is to be oriented toward minimizing the overall cost of water treatment to meet discharge requirementsthis will include not only water treatment equipment but also sludge handling/management. The other flow sheet is to be oriented toward also meeting discharge requirements but includes the recovery of products from the water (copper, metal sulfates, etc.) to potentially offset treatment costs and result in overall better economics.
The project will evaluate proven technologies as well as technologies with credible pilot-scale supporting data. Technologies with only laboratory testing history will not be included, which would include technologies for sludge management, solid/liquid separation, dewatering, drying, etc., as well as technologies for product recovery from water. The goal is to assemble the sequence of unit operations resulting in the most attractive overall economics.
A uniform cost estimating approach was developed and documented to ensure that consistent assumptions and uniform approaches are used for all scenarios evaluated. A conceptual design of a filter cake repository was completed. This was important because a repository location had only recently been established, allowing reasonable cost estimates to be prepared for the first time. Two flow sheets were identified to be used as baseline references with which to compare possible improvements. An extensive verification effort was performed to place both reference flow sheets on the same design basis and perform cost estimates and economic analyses consistent with the approach mentioned above. This verification effort included technical verification as well as economic verification. A result of the verification effort was that sludge dewatering was found to be extremely expensive; since discharge of sludges to the Berkeley Pit is an option requiring study before approval, a small-scale test program was conducted to evaluate the effects of returning settled sludges to the Berkeley Pit for a 30-year period. Another significant result of the verification effort was that the cost of using a strong oxidant for iron oxidation and removal prior to recovery of other metals was exorbitant; therefore, other methods for iron oxidation at low pH were investigated. The most promising was found to be Inco's sulfur dioxide/air process used to oxidize cyanide, which was investigated at bench scale by Inco with very encouraging results. Various trade studies were performed, for example, evaluating a high-density sludge system versus a conventional precipitation system. An evaluation was performed to evaluate the feasibility of on-site upgrading of raw products to increase their marketability and value. For example, a metal recovered as a carbonate could be calcined to an oxide, thereby, increasing its grade and reducing shipping costs.
The project goal is to provide information to support technical feasibility and regulatory acceptance of phosphoric acid-based in situstabilization of lead in residential soils at the Joplin, Missouri National Priorities List Site. The ultimate goal is to demonstrate this technique is a cost-effective alternative to excavation and haulage of metal-contaminated soils to a waste repository.
The remediation approach involves mixing commercial grade phosphoric acid and a trace of potassium chloride into near surface soils, followed by pH adjustment (e.g., with lime addition) to attain paraneutrality. As a result, soluble lead is converted to pyromorphite, a highly insoluble and environmentally stable mineral. Subsequently, lead uptake from rooting zone soils (into aboveground plant biomass) and into the bloodstream of young children (from the gastrointestinal tract) is significantly reduced.
The following project planning documents were completed in fiscal 2000: Work Plan; Quality Assurance Project Plan; NEPA Compliance/Site Access Agreement; and a Health and Safety Plan. The subcontract with the Missouri Department of Natural Resources (MDNR), Hazardous Waste Division, for field and document preparation support was completed. The subcontract with the University of Missouri's Veterinary Medical Diagnostic Laboratory for soils characterization and pig dosing studies was nearly completed. The U.S. Environmental Protection Agency (EPA)/Las Vegas' Environmental Monitoring Laboratory agreed to perform in vitro assessments of lead bioaccessibility, as requested by EPA Region 7 and funded by EPA's Office of Solid Waste and Emergency Response. MDNR personnel began to mobilize for the field treatment work in mid-September 2000.
Revegetation of Mining Waste Using Organic Amendments and
Evaluate the Potential for Creating Attractive Nuisances for Wildlife
The objectives of this project are to demonstrate the use of organic amendments to enhance the establishment and growth of grass on lead mine tailings and to evaluate the affect of those amendments on plant uptake of metals. Two sources of compost and an organic fertilizer derived from municipal sewage treatment plant sludge were incorporated into two types of tailings near Desloge, Missouri, and the replicated plots were planted with grass. Both types of tailings (fine-textured floatation tailings and course-textured gravity separation tailings referred to as chat tailings) contain elevated concentrations of lead, zinc, and cadmium. This project will be evaluated for three growing seasons.
Thousands of abandoned mine and mineral processing sites throughout the United States are very unattractive and can be a significant environmental hazard. The federal government and responsible parties need to develop cost-effective remedial approaches to effectively manage these large areas that are contaminated with a wide variety of metals. Natural revegetation is often prevented in these areas because of low pH, phytotoxic concentrations of metals, poor physical structure for plant growth, nutrient deficiencies, and slopes too steep for plant establishment. Mine waste reclamation research frequently includes the addition of organic soil amendments, since mine waste materials are typically subsurface in origin and have minimal organic content. However, the diversity of organic amendments used and the lack of uniformity within each category of material make comparisons among sites and studies difficult. In addition, while it is generally agreed that organic amendments are capable of stabilizing mine waste metals, the potential for post reclamation impacts to wildlife due to plant uptake of those metals requires further research.
MSE Technology Applications, Inc., established field plots at the Big River Mine Tailings Site and the Leadwood Chat Tailings Site in Missouri in the spring of 2000. The plots were evaluated to determine vegetation establishment, biomass production, and plant uptake of metals. Procedures for establishing, maintaining, and evaluating the plots will be broadly applicable and reproducible so that subsequent studies at other locations will produce comparable information. The three organic amendments are milorganite, ormiorganics compost, and St. Peters compost. These amendments were applied at a low, medium, and high application rate. Each amendment/application rate combination was replicated four times including a control plot that only received the inorganic fertilizer at both sites, totaling 80 plots. The plant species for the demonstration was tall fescue (Kentucky variety). The plots were monitored monthly from May through September 2000. The project will be evaluated for three growing seasons.
Figure 25 shows the Leadwood Chat Tailings site prior to planting, and Figure 26 shows the site after incorporating the organic amendments and 7 months of growth. Figure 27 shows the Big River Mine Tailings site prior to planting, and Figure 28 shows the site after incorporating the organic amendments. At the end of the first growing season, vegetative cover and biomass production were quantified, and tailings and vegetation samples were obtained and analyzed. Preliminary results indicate the amendments improve both establishment and growth, differences among amendment types and application rates are significant, and plant uptake to metals is not great enough to impact area wildlife. Additional results of the first growing season will be discussed in an Interim Report to be issued in March 2001. Project completion is expected in December 2002.
Acid Mine Drainage (AMD) emanates from many abandoned mine sites in the western United States. Such drainage, having an elevated content of dissolved metals and low pH, presents an environmental problem that needs to be economically addressed. Sulfate-reducing bacteria (SRB) have the ability to immobilize dissolved metals, by precipitating them as sulfides, and increase pH provided that a favorable biochemical environment is created. Such conditions may be created by constructing artificial wetlands, if space is not limited, or converging the AMD flow to an engineered passive SRB reactor.
A SRB reactor contains an organic-carbon chamber that is vital for its operation. A life span of a properly designed reactor depends on the organic carbon supply, permeability of organic-carbon chamber, and the capacity of the reactor to accumulate precipitated sulfides.
When the source of organic carbon is depleted, or becomes unavailable, because permeability of the organic matter decreased due to settling processes or physical or chemical encapsulation, the bioreactor will cease operating. To reactivate such a bioreactor, the organic carbon source has to be either replenished or rejuvenated. Therefore, it is desirable to: 1) maximize the time interval between such operations; and/or 2) be able to predict the longevity of the carbon source to economically optimize the reactor's size.
Similarly, when the capacity of the bioreactor's chamber that was designed to hold precipitated sulfides is exhausted, the sulfides will either break through or the reactor will plug ceasing its operation.
This project addresses engineering improvements that include replacing the organic carbon supply-system in a SRB reactor and refining how the reactor is sized.
Engineered improvements of SRB reactors are to be accomplished by implementing the four tasks listed below.
Task ISelecting Optimal Media with Organic Carbon
The optimal media needs to: 1) contain a sufficient amount of organic carbon; 2) be used economically as passive SRB bioreactors; and 3) have high potential to be permeable when saturated with water. Determination of the optimal organic carbon media will be done through a literature study. A data base will be set up that will include the media technical parameters, records of use, availability, price index, etc.
Task IIDesigning a Permeability and Contact Time Enhancing
PACTES will ensure a good supply of organic carbon and will maintain good permeability of the organic matter throughout the predicted life of the reactor.
Task IIIDesigning an Organic Carbon Replaceable Cartridge
A replaceable cartridge system will be easy to install and replace in a bioreactor, particularly at a remote location.
To ensure that PACTES and RCS systems are compatible, their development will be symbiotic. Work on each system will include the following phases: 1) developing a list of concepts for each system; 2) narrowing the list to one or two of the most applicable solutions; 3) laboratory testing of the selected solutions; 4) preparing the design document; 5) constructing the prototype of the RCS combined with PACTES; and 6) bench-test study of the constructed prototype.
Task IVDeveloping a Computer Software to Simulate SRB
Activities in the Bioreactor
The software will enable a designer to efficiently design and size a bioreactor by quantifying the expected rate of organic carbon depletion and the volume of SRB activity by-products.
The project was initiated in January 2000 with efforts focusing on Task I as scheduled. The literature study resulted in developing a data base, assembled with Microsoft Access, that included 88 records relevant to using various organic substances as an organic carbon source for SRB. A review of the records revealed that there have been more than two dozen organic media used for providing organic carbon for SRB. A rating of these media according to their efficiency indicates that compost, food product sewage, cow manure, and poultry waste are most suitable to supply organic carbon for SRB. Nevertheless, other factors like availability and cost must be taken into consideration when selecting organic carbon for the given location. Based on these conclusions, cow manure was recommended to be used as the organic carbon source for the efforts that will be implemented in Tasks II, III and IV.By the end of fiscal 2000, Task II was advanced through the development of concepts for the PACTES using a mixture of cow manure prepacked in plastic-net socks, approximately one cubic foot in volume. Two kinds of mixtures are currently being considered: 1) cow manure with walnut shells; and 2) cow manure with strips of corrugated plastic and pumice stone. Walnut shells and corrugated plastic will increase the permeability and prevent settling of the mixture. In addition, walnut shells and pumice stone will provide a solid matrix for SRB growth.
Task III was also advanced to the development of concepts for the RCS that currently include a pattern of pipes filled with PACTES. The pipes will be placed in a container through which the AMD will flow in a vertical direction collinear with the axes of the pipes.
Initial work on Task IV identified an existing software, MINTEQAK, that was developed to simulate biochemical processes occurring in wetlands. This software must be modified to enable input of variables for the time and spatial coordinates.
Work on the project will continue into fiscal 2002.
All figures and tables can be found in the Mine Waste Technology Annual Report. (PDF, 5.6 M, 74 pp)