Completed Activities - Activity III
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Activity III Overview
The objective of this activity is to demonstrate innovative and practical remedial technologies at selected waste sites, a key step in proving value for widespread use and commercialization. Technologies and sites are selected primarily from the prioritized lists generated in the Volumes from Activity I, or they may be a scale-up from bench-scale experiments conducted under Activity IV.
Acidic metal-laden water draining from remote, abandoned mines has been identified by the U.S. Environmental Protection Agency (EPA) as a significant environmental hazard to surface water in the western United States. In Montana alone, more than 3,000 such sites have been identified, and wastes from these mines have damaged over 1,100 miles of surface water in the State.
EPA asked MSE Technology Applications, Inc., to develop a treatment facility at one of these sites to treat acidic metal-laden water. Due to the remote nature of these locations, this facility was required to operate for extended periods of time on water power alone, without operator assistance.
The Crystal Mine, located 7 miles north of Basin, Montana, is an example of a remote mine site with a point-source aqueous discharge, which made it an ideal site for this demonstration. In addition, the site had been identified by the Montana State Water Quality Bureau as a significant contributor of both acid and metal pollution to Uncle Sam Creek, Cataract Creek, and the Boulder River. This project demonstrated a method for alleviating nation-wide environmental problems associated with remote mine sites.
The Crystal Mine demonstration treated a flow of water ranging from 10 to 25 gallons per minute, approximately half of the total mine discharge. The process consisted of the following six unit operations:
- Initial Oxidation-atmospheric oxygen partially oxidizes ferrous iron to the ferric form.
- Alkaline Addition-reagents form metal hydroxide solids.
- Secondary Oxidation-atmospheric oxygen oxidizes additional ferrous iron to the ferric form.
- Initial Solid/Liquid Separation-settling ponds trap precipitated solids.
- pH Adjustment-atmospheric carbon dioxide lowers the pH.
- Secondary Solid/Liquid Separation-settling pond retains additional precipitated solids.
The Remote Mine Site Demonstration Project at the Crystal Mine was conducted in the field for 2 years under all weather conditions. Construction of buildings, ponds, and associated mine site infrastructure began in late May 1994 and was completed in early August 1994. Acid mine drainage from the lower portal of the Crystal Mine began passing through the system on a full time basis in early September 1994. Analytical data from the project showed a greater than 75% removal of toxic metals from the mine drainage. The project was closed out, and the final report was published (PDF, 829 Kb, 64 pp).
Surface and ground water inflow into underground mine workings becomes a significant environmental problem when water contacts sulfide ores, forming acid drainage. Clay-based grouting, the technology selected for this demonstration, has the ability to reduce or eliminate water inflow into mine workings by establishing an impervious clay curtain in the formation.
Ground water flow is the movement of water through fissures and cracks or intergranular spaces in the earth. With proper application, grout can inhibit or eliminate this flow.
Grouting is accomplished by injecting fine-grained slurries or solutions into underground pathways where they form a ground water barrier. The Ukrainian clay-based grouting technology was selected for testing and evaluation because it offered a potentially long-term solution to acid mine drainage problems.
Clay-based grouts are visco-plastic systems primarily comprised of structure-forming cement and clay-mineral mortar. When compared to cement-based grouts, clay-based grouts offer the following advantages: better rheological characteristics, greater retention of plasticity through the stabilization period, and less deterioration during small rock movement.
The Mike Horse Mine near Lincoln, Montana, was the project site. A major factor in the site selection was an identified point-source flow from Mike Horse Creek into the mine causing acid drainage that could potentially be controlled using grouting technology.
Approximately 1,600 cubic yards of clay-based grout were injected into the fracture system adjacent to the Mike Horse Mine. The grout was pumped into boreholes using packers to ensure the proper placement of grout at selected intervals. Grout injection was initiated in September 1994 and was completed in November 1994. A second phase of grout injection was planned for the summer of 1995; however, high water dammed up within the mine caused extensive damage to the mine and to the monitoring stations used for the demonstration. As a result, Phase Two was discontinued.
From the minimal amount of monitoring data that was collected, it was determined that the total discharge from the mine was reduced by approximately 30%.
The final report was published (PDF, 257 Kb, 20 pp).
The presence of nitrates in water can have detrimental effects on human health and the environment. Nitrates may be present in mine discharge water as a result of mining or other industrial activities.
To comply with federal and state water quality standards, mining companies have typically used ion exchange or reverse osmosis to remove nitrates from discharge water. However, both are expensive and generate a concentrated nitrate wastestream requiring disposal.
Mine Waste Technology Program (MWTP) personnel undertook an extensive search to evaluate innovative nitrate removal technologies. Of the twenty technologies screened, the following three showed the most promise in making nitrate removal more economical and environmentally responsible:
- ion exchange with nitrate-selective resin;
- biological denitrification; and
- electrochemical ion exchange (EIX).
MWTP personnel believed the best solution to the nitrate problem was some combination of the three technologies that balanced capital costs with operating costs, reliability, and minimization of wastestreams requiring disposal. Each combination had advantages and disadvantages that were addressed during the project.
The Nitrate Removal Demonstration Project was conducted at the TVX Mineral Hill Mine near Gardiner, Montana. Conventional ion exchange was used to remove nitrate from the mine water and produce a concentrated brine for additional testing. Biological denitrification units and an EIX unit were used to process both mine water and concentrated nitrate brine.
The goals of the project were to remove nitrate to less than 10 milligrams per liter (mg/L) of nitratenitrogen (NO3-N) in the effluent and to minimize the amount of waste produced. Of all the technology combinations tested, biological denitrification of concentrated nitrate brine was the most successful at meeting these goals.
The nitrate ion exchange (NIX) unit was produced by Altair, Inc. As expected, the NIX unit worked well and removed nitrate from the mine water very effectively. Input levels of 20 to 40 mg/L NO3-N were typically reduced to less than 1 mg/L. The unit also produced a concentrated brine with high levels of nitrate and chloride. Frequent equipment shutdowns and muddy mine water did not affect the operation of the NIX unit.
Biological denitrification was performed on both mine water and concentrated brine. This process worked well to eliminate nitrate in brine. Except for two process upsets, nitrate was removed to levels less than 10 mg/L NO3-N. This removal rate met the project goals and was typically greater than 99%.
Biological denitrification of the raw mine water was less successful. A removal rate of approximately 50% was typically achieved. This data was taken from an operating denitrification reactor at the mine. Past data had shown that this reactor was very effective at nitrate removal. Apparently, the frequent shut downs and startups had a detrimental effect on these reactors.
The electrochemical ion exchange unit was built be Selentec, Inc. Electrochemical ion exchange was unsuccessful at removing much nitrate from the concentrated brine because of the presence of high concentrations of a competing anion-chloride.
Electrochemical ion exchange was able to remove nitrate from the raw mine water more effectively than from the brine. Nitrate was removed at first; however, fouling of the resin by dirty water occurred quickly, and the process was rendered ineffective after one batch. Filters were installed, but the nature of the particles made filtration difficult.
The final report was published (PDF, 1 M, 69 pp)
The primary use of cyanide in the mining industry is to extract precious metals from ores. The use of cyanide has expanded in recent years due to increased recovery of gold using heap leach technologies. Cyanide can be an acute poison and can form strong complexes with several metals, resulting in increased mobility of those metals. As such, cyanide in mine wastewater can contribute to environmental problems.
These potential problems have led to the development of several methods to destroy cyanide and cyanide complexes in mining wastewater. Most of these processes use chemicals to oxidize the cyanide and produce nontoxic levels of carbon dioxide and nitrogen compounds, which are relatively expensive to operate.
Biological destruction of cyanide compounds is a natural process that occurs in soils and dilute solutions. To take advantage of this natural destruction, a strain of bacteria was isolated by researchers at Pintail Systems, Inc. This bacteria has been tested on cyanide-contaminated mine waters and has shown degradation rates of over 50% in 15 minutes.
The main goal of this project was to use a strain of bacteria to destroy cyanide associated with precious metal mining operations. Another project goal was to develop a reactor design that would best use the cyanide-degrading effects of the bacteria to destroy cyanide from mining wastewater.
The field demonstration portion of the project was located at the Echo Bay McCoy/Cove Mine, southwest of Battle Mountain, Nevada. The mining rate at the mine exceeds 160,000 tons of ore per day. Milling of high-grade and sulfide ores occurs simultaneously with the cyanide solution heap leaching of lower grade ores. These cyanide solutions contain 500 to 600 mg/L of weak acid dissociable (WAD) cyanide with other contaminants, such as arsenic, copper, mercury, selenium, silver, zinc, and nitrate.
In fiscal 1996, a field-scale unit was constructed at the McCoy/Cove Mine to degrade cyanide in an existing process stream. The unit was designed to reduce the WAD cyanide concentration from 500 mg/L to less than 0.2 mg/L at flow rates of approximately 1 gallon per minute.
A bioaugmentation phase was initiated to isolate organisms and select the ones that degrade cyanide most effectively. To initiate the project, Pintail Systems, Inc., collected water samples from the mine site to isolate indigenous organisms capable of effectively degrading cyanide and performed bioaugmentation studies at their Colorado laboratory. During the bioaugmentation phase, the bacteria were subjected to increasing concentrations of cyanide to select the most capable organisms.
The bacteria selected during the bioaugmentation process were then placed on fixed growth media in bench-scale reactors. Next, actual cyanide mine water was processed through the reactors to study the kinetics of cyanide degradation. The results from these tests were used to design the pilot-scale reactors to be used at the mine. The process train consisted of tanks where the aerobic and anaerobic bacteria were grown in large quantities. The bacteria were then pumped to the reactors for reinoculation. The cyanide solution entered the aerobic reactor first where aerobic organisms degraded a large portion of the cyanide. The solution then moved through a series of anaerobic units for further degradation. Finally, an aerobic polishing step removed the last traces. Since cyanide is known to degrade by mechanisms other than biological, a series of control reactors was installed to run concurrently with the biological reactors.
Testing of the pilot-scale unit was performed during the summer of 1997. Cyanide and heavy metals were substantially removed from the mine process water. The pH was consistently neutralized. A preliminary scale-up cost estimate indicated substantial savings over conventional technologies.
The final report was published. (PDF, 1.2 M, 59 pp)
Personnel from the U.S. Environmental Protection Agency's National Risk Management Research Laboratory forwarded this project to the Mine Waste Technology Program (MWTP). The concept of the pollutant magnet was to develop, produce, and test particles that have specific magnetic properties and have the ability to remove specific pollutants from a wastestream. After program personnel reviewed the project, it was dropped from MWTP due to its similarity with competing technologies that were more developed and had a nonmining specific use.
The Arsenic Oxidation Project was proposed to demonstrate and evaluate arsenic oxidation and removal technologies. The technology being demonstrated during this project was developed jointly by the Cooperative Research Center for Waste Management and Pollution Control Limited and the Australian Nuclear Science & Technology Organization (ANSTO) from Lucas Heights Research Laboratories in Lucas Heights, New South Wales, Australia.
Arsenic contamination in water is often a byproduct of mining and the extraction of metals such as copper, gold, lead, zinc, silver, and nickel. This contamination will continue to grow as high-grade ores with low arsenic content are being depleted and the processing of sulphide ores with high arsenic content becomes increasingly common. In most cases, it is not economical to recover the arsenic contained in process streams because there is little demand worldwide for arsenic. Arsenic can be present in leachates from piles of coal fly ash, in contaminated ground waters, in geothermal waters, and in acid drainage from pyritic heaps resulting from the past practices of mining metallic ores.
Trivalent arsenic, arsenite, or As+ compounds have been reported to be more toxic than the corresponding pentavalent arsenic, As+5 or arsenate forms, and much more difficult to remove from solution. Consequently, there is a need to convert As+3 to As+5 to achieve effective arsenic removal from solution.
The small-scale pilot project demonstrated a two step process for removing arsenic from contaminated mine water. The first step and primary objective of this project was to evaluate the effectiveness of a photochemical oxidation process to convert dissolved As+3 to As+5 using dissolved oxygen as the oxidant. The technology provides a method for the oxidation of As+3 in solution by supplying an oxidant, such as air or oxygen, and a nontoxic photo-absorber, which is capable of absorbing photons and increasing the rate of As+3 oxidation to the solution. The photoabsorber used is economical and readily available. Ultraviolet oxidation using high-pressure mercury lamps and solar energy was tested. The second step of this project resulted in removing As+5 from the solution by using an accepted U.S. Environmental Protection Agency method, adsorption using ferric iron.
The field demonstration and final report were completed. The photochemical oxidation process was very effective at oxidizing arsenite to arsenate at optimum conditions in the batch mode for both the solar tests and the photoreactor tests; however, design problems with the photoreactor unit in the continuous mode would not allow ANSTO to achieve their claim of 90% oxidation of arsenite in solution. Channeling of the process waters in the photoreactor unit was the reason for poor oxidation of arsenite, and steps to correct the problem during the field demonstration were unsuccessful. Modifications to the baffle system are necessary to prevent further channeling.
The purpose of the Arsenic Removal Project was to demonstrate the effectiveness of two innovative technologies and the best demonstrated available technology (BDAT) to remove arsenic from mineral industry effluents to below 50 parts per billion (ppb). Table AIII, P9-1 shows the removal and economic analysis of these tests. Two of the treated effluent streams were from the ASARCO East Helena lead smelter; the scrubber blowdown water contained >3 grams per liter arsenic and other associated metals, and the water treatment thickener overflow water contained approximately 6 parts per million arsenic. A third stream from the TVX Mineral Hill Mine 1,300- foot portal ground water contained approximately 500 ppb arsenic.
The concept of this process is to strip arsenic (as arsenate) from solutions in a manner to produce mineral-like precipitated salts. The concept is to substitute arsenate into an apatite structure, thereby, forming a solid solution compound that would be thermodynamically stable in an outdoor storage environment.
In this technology, arsenic is removed from solution by adsorbing it onto the surface of aluminum oxide over a specific pH range. After absorption, reagents are added to the alumina to desorb the arsenic into a concentrated brine. The concentrated arsenic brine solution is then treated using an iron adsorption technology to remove and stabilize the arsenic. The activated alumina in the process is recycled following the desorption process by treatment with sodium hydroxide.
Ferrihydrite technology is the BDAT. For ferrihydrite adsorption to occur, ferric iron (Fe+3) must be present in the water. Dissolved arsenic is removed by a lime neutralization process in the presence of the ferric iron, which results in the formation of arsenic-bearing hydrous ferric oxide (ferrihydrite).
All three technologies (iron coprecipitation, alumina adsorption, and mineral-like precipitation) showed favorable results for arsenic removal using ground water; however, using industrial process wastewater, only two of the technologies (mineral-like precipitation and ferrihydrite adsorption) were capable of removing arsenic to below discharge standards. The complex chemistry of the industrial wastewater had a profound effect on arsenic removal using alumina adsorption.
All work was completed, and the final report was published.(PDF, 3.5 M, 116 pp)
Cyanide is used in the mining industry to dissolve precious metals from ore but can contribute to environmental problems. This has led to the development of technologies to degrade cyanide and cyanide complexes in mine wastewater and spent ore heaps. Most of these processes use chemicals to oxidize cyanide and are expensive to operate. Therefore, biological detoxification has been proposed as an alternative to chemical treatment for decommissioning heap leach operations.
Three biological technology providers were contracted to participate in a long-term study in which the effectiveness of their technology was compared with hydrogen peroxide and process rinse water.
This project demonstrated four biological technologies. Project objectives were to:
- reduce the concentration of the effluent weak acid dissociable (WAD) cyanide to meet National and State regulatory standards within a reasonable period;
- determine final affects of biological treatment on related discharge parameters (pH, sulfates, nitrates, metals, and gold recovery); and
- determine technology cost compared to conventional detoxification methods. Column testing began on December 3, 1998, and operated 158 days until May 17, 1999.
The standard hydrogen peroxide rinse column was demonstrated to have the highest WAD cyanide degradation rate. The regulatory limit of <0.2 milligrams per liter was reached in 36 days. The process rinse water column showed a cyanide degradation curve of approximately one-third as high as the hydrogen peroxide rinse column.
One technology provider reached the regulatory limit in 151 days. The remaining three biological processors were slightly quicker than the process rinse water and were approaching the regulatory limit at termination of the demonstration.
All work was completed, and the final report was published.
The foremost cause of childhood lead poisoning in the United States is the ingestion of lead-based paint found in older housing. The overall objective of this demonstration was to obtain cost and performance data on an innovative set of technologies capable of removing lead-based paint from interior decorative wood in residential housing with minimal damage to the underlying substrate and no residual hazardous waste.
The technologies evaluated included the paint removal system PR-40/LEADXT/PR-40AFXT and a carbon dioxide blasting technology.
The paint removal system PR-40/LEADXT/ PR- 40AFXT was demonstrated to effectively remove lead-based paint and/or lead-based varnish from interior decorative wood with minimal apparent damage to the wood substrate within certain operational limitations. The product proved effective when previous paint/varnish layers were between six to eight layers. Other wall coverings beneath the paint surface (i.e., wallpaper or wall texturing) further impacted penetration of PR- 40/LEADXT/PR-40AFXT.
The carbon dioxide blasting technology was effective in removing the lead-based paint only in areas where PR-40/LEADXT/PR-40AFXT had achieved full penetration of all paint layers. However, the blasting technology produced an unsatisfactory erosion of soft wood leaving the surfaces feathered and/or gouged.
Sulfate-reducing bacteria (SRB) are a well-known, effective method for treating acid mine drainage (AMD). With the proper conditions of solution temperature and oxidation/reduction potential, and with suitable nutrients available to the SRB, sulfate is electrochemically reduced to sulfide, which forms insoluble precipitates with many metals. In addition, alkalinity is produced that serves to raise the solution pH. Previous and current Mine Waste Technology Program projects have successfully demonstrated SRB in remote locations with the goal of providing improved water quality at low cost. Advances have been made in engineered systems utilizing SRB, particularly in the area of providing cheap nutrients to the bacteria, which significantly enhance overall system economics. These advances increase the possibility of utilizing SRB as part of an AMD treatment system in which selected metals are separated and recovered for resale, offsetting overall treatment costs. This project demonstrated and evaluated a process with the potential to profitably recover copper, zinc, and sodium hydrosulfide from Berkeley Pit water.
Biomet Mining Corporation of Vancouver, British Columbia, has patented a method utilizing combustion products from natural gas as nutrients for SRB, called the Biosulfide process. This cheap source of nutrients has enabled Biomet to show favorable economics in recovering copper and zinc products from AMD at pilot-scale at several locations in North America. Copper is recovered directly as copper sulfide using hydrogen sulfide gas produced by SRB. Following a pH adjustment using the alkalinity produced by the SRB, hydrogen sulfide gas is used to recover zinc as zinc sulfide. Other products, including sodium hydrosulfide and sulfuric acid, can be produced with downstream processing if the economics at a specific location are favorable.
Bench-scale miniplant testing began at the MSE Technology Applications, Inc. (MSE) facility in October 1998. Biomet performed laboratory tests to determine initial pH and oxidation/reduction potential conditions for copper and zinc separation/recovery from September to November 1998. Biomass development was performed at MSE with the pilot-scale system between December 1998 and May 1999. Biomet moved the pilot system to the Berkeley Pit in May 1999, and MSE had virtually no involvement in the project after that time due to budgetary constraints. Pilot scale operation continued at the Berkeley Pit until September 1999, at which time the pilot system was shut down with tentative plans to restart in April 2000. Pilot-scale operation was plagued with operational problems, particularly related to the performance and reliability of the natural gas burner and to the sulfate reduction performance of the bacteria. At the direction of the U.S. Environmental Protection Agency, MSE terminated support of the project in December 1999.