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Minerals 2017, 7(3), 46; https://doi.org/10.3390/min7030046

Article
Mining-Related Selenium Contamination in Alaska, and the State of Current Knowledge
1
Department of Mining and Geological Engineering, University of Alaska Fairbanks, 306 Tanana Drive, Fairbanks, AK 99775, USA
2
Department of Process Engineering, Stellenbosch University, Banghoek Rd, Stellenbosch 7600, South Africa
3
Department of Civil and Environmental Engineering, University of Alaska Fairbanks, 306 Tanana Drive, Fairbanks, AK 99775, USA
*
Author to whom correspondence should be addressed.
Academic Editor: Tuncel M. Yegulalp
Received: 9 December 2016 / Accepted: 12 March 2017 / Published: 21 March 2017

Abstract

:
Selenium pollution has been a topic of extensive research dating back further than the last decade and has attracted significant attention from several environmental and regulatory agencies in order to monitor and control its discharge from myriad industrial sources. The mining industry is a prime contributor of hazardous selenium release in the aquatic systems and is responsible for both acute and chronic impacts on living organisms. Herein we provide an overview of selenium contamination issues, with a specific focus on selenium release from mining industries, including a discussion of various technologies commonly employed to treat selenium-impacted waters from mining discharge. Different cases pertaining to selenium release from Alaskan mines (during years 2000–2015) are also presented, along with measures taken to mitigate high concentration releases. For continued resource exploration and economic development activities, as well as environmental preservation, it is important to fundamentally understand such emerging and pressing issues as selenium contamination and investigate efficient technological approaches to counter these challenges.
Keywords:
selenium; waste; mine; treatment; removal

1. Introduction

Selenium release and pollution is a worldwide phenomenon that results from a wide variety of anthropogenic activities, such as agriculture, mining, and other process industries. Selenium is a potentially toxic element, and mining-related selenium release was a major concern during the last decade as high concentrations were reported at some mine sites in the US [1,2]. Selenium contamination is vast, affecting both aquatic and terrestrial ecosystems, and has therefore attracted the attention of natural resource and water quality regulators around the world. Consequently, monitoring and pollution control efforts for selenium have been widely expanded.
Selenium is a naturally occurring semi-metal belonging to the chalcogen group and typically does not occur in pure elemental form. It is a trace element in natural deposits of ores containing other minerals, such as sulfides of heavy metals, but there are no specific geologic deposits in which selenium is a major constituent. The major sources of selenium are black shale, phosphate rocks, coal, and limestone. Selenium can also be found in rare minerals, such as Eucairite (CuAgSe), Crooksite (CuThSe), and Clausthalite (PbSe). Selenium is commonly produced as a by-product of other base metals and is widely used in metallurgy and in the manufacturing of glass, chemicals and pigments, electronics, fertilizers, etc. Although only present in trace amounts, mining operations expose selenium-bearing elements to air and water. This mobilizes selenium into aquatic systems where it bioaccumulates in the food chain, thereby escalating its hazardous effects. However, the levels of selenium released can be minimized by controlling and treating the effluents from mining operations.
This article provides a brief introduction to selenium chemistry and toxicity, presents a detailed review of currently available techniques for removing selenium from industrial/mining wastewater, and discusses mining-related selenium contamination from Alaskan mines.

Chemistry, Environmental Fate, and Effects of Selenium

Selenium exists in the environment in organic and inorganic forms. The speciation of selenium determines its available form and is governed by physical, chemical and biological processes. This discussion will be focused on the inorganic forms, which are of prime concern to the mining industry. Inorganic selenium exists in multiple oxidation states, the most common being −2, 0, +4 and +6, which show different chemical and toxicological properties. These characteristics of selenium are affected by the redox conditions and pH, which also plays a crucial role in designing any selenium treatment processes. Figure 1 shows a Pourbaix diagram representing different oxidation states of selenium in an aqueous phase at different pH and reduction potential (Eh) conditions. From the figure, it can be seen that in the pH range of 4 to 9, which is the approximate range under which most natural systems (e.g., soil, water) exist, the selenate (SeO42−) species is found to be more dominant under strongly oxidizing conditions (pe > 8). As we move down along the y-axis to a more reducing environment, the selenate is reduced to selenite (SeO32−) for alkaline pH and to hydrogen selenite for acidic and neutral pH. Finally, in reducing conditions it exists in the −2 oxidation state as selenide (Se2−) [3]. The occurrence of selenium in different oxidation states is also affected by the type of surrounding elements and ions.
However, the speciation standalone does not describe the toxic effect of selenium; instead, factors such as bioavailability, bioaccumulation, and biotransformation should be considered while evaluating its toxic effect.
Selenium is also an essential element for various animals and fish. Studies relating to deficiency of selenium have reported it as one of the major cause of reduced growth, muscular dystrophy, and increased mortality in fish and aquatic birds [5,6]. Similarly, elevated selenium concentrations have short-term (acute) and long-term (chronic) effects depending upon the exposure concentration and duration. Because of the tendency for selenium to bioaccumulate in different species, it has been difficult for the United States Environmental Protection Agency (EPA) to quantify permissible selenium content in water. Also, the uptake of selenium by biota can be via two different pathways: from the water or through the diet. 1999 EPA selenium criterion for water was based on dissolved concentration values. However, updated 2016 EPA criteria include the upper limits in terms of tissue residue for different fish organs [7]. The tissue based criteria are then used to derive the water column criteria which are summarized in Table 1. The advantage of tissue residue based criterion is that it allows a measure of assessment of toxicological hazard which is more species and site specific.

2. Historical Relevance of Selenium in Mining Industry

The mining industry is one of the prime contributors of selenium release into the environment. The mining of coal, precious metals (gold and silver), and metallic sulfides are key contributors of selenium from mining operations [1]. According to an annual coal report presented by the US Energy Information Administration, the annual coal production for 2015 was about 896 million short tons, which was used for electric power generation [8]. The burning of coal produces ash enriched in selenium, which is then concentrated at the disposal sites of different power plants [9]. Subsequently, selenium can be leached out by rainwater, thereby contaminating groundwater and nearby aquatic systems [10].
Mining and processing of metallic ore deposits release selenium into the environment through waste rock disposal and tailings produced at the mine site. In metallic ore deposits, selenium is associated with sulfur-containing ores, such as pyrite, sphalerite, chalcopyrite, and other sulfides. These sulfide-containing ores are prevalent in the mining of metals, such as copper, silver, lead, zinc, and uranium. Ore processing involves methods such as froth flotation and leaching, which involves chemical treatment of slurry (solids in water) that results in dissolution of selenium in water. This dissolved selenium, when discharged through tailings or wastewater streams, increases the risk of bioaccumulation in aquatic life. Proper measures, such as controlling oxidation of selenium and continuous monitoring of selenium content in various discharge streams, should be taken by waste management systems to ensure minimal discharge of selenium to the ecosystem.
The appropriate way to reduce the potential for selenium contamination from mining activities is to minimize surface disposal of wastewater and tailings. Waters containing high selenium concentrations can be treated prior to discharge through various chemical and biological techniques, including water recycling, in situ leaching processes and backfilling of solids. Table 2 shows the concentration of selenium in various environmental matrices from oil and mineral industry sources, and Figure 2 shows selenium transport in the environment from mining operations.
Another major source of selenium in the environment is atmospheric release through pyrometallurgical treatment of metallic ores to recover metals, such as copper, nickel, lead, and zinc. This involves the process of smelting in which the volatile inorganic forms of selenium (Se (0), SeO2, H2Se) are vaporized, emitted into the atmosphere, and deposited back to nearby land. There are various theories describing the mechanisms of inorganic selenium transformation and deposition, but further research is needed [17].

3. Selenium Treatment Technologies

Tailings discharge from mining operations contains selenium in aqueous form as selenate and selenites. Various tailings discharge treatment methods are employed by the mining industry to prevent, control and remove selenium content at the source. These methods can be classified into three major categories that are discussed below: (a) physical treatment, (b) chemical treatment, and (c) biological treatment.

3.1. Physical Treatment

Physical treatment methods that are widely used on an industrial scale for selenium removal include membrane filtration, media filtration, and ion exchange. They are the conventional methods employed for industrial wastewater treatment and are relatively simple in operation compared to other treatment methods. Membrane filtration utilizes a semi-permeable membrane to which a pressure gradient is applied, resulting in the contaminants being retained on the membrane (retentate) and clean water being forced through it (permeate). Membrane filtration technologies are further classified as microfiltration, ultrafiltration, nanofiltration, and reverse osmosis (RO), depending on the filtration size. Additionally, these processes differ in the type of membranes used and the operating pressure range for separation. The advantage of using membrane technology is its capability to produce very high-quality permeate. It is most often used for water reuse, boiler feed water, and drinking water applications [2]. However, membrane filtration is an expensive method and poses operational challenges, such as fouling and scaling of the membrane, disposal, and the requirement for pretreatment such as filtration to remove organics. Also, these methods are sensitive to other ions, such as nitrates, sulfates, and chlorides, which renders selenates inactive, causing them to respond poorly to separation processes. Of the four methods, RO has been successfully implemented for mine wastewater treatment. For example, a permanent RO facility was successfully established at Barrick’s Richmond Hill Mines (Lead, SD, USA) as a post step after using iron reduction and precipitation for the treatment of mine water [18].
Another physical method is ion exchange, which is widely used for wastewater treatment. Ion exchange works by adsorbing undesirable ions on a solid or gel surface present in water and reversibly releasing other appropriate ions into the solution. The solid surface can be a resin or synthetic zeolite, known as a polystyrene resin. The process can be used for the preferential treatment of ions as well, however, its application for selenium treatment has not been successful because selenium in the form of selenates has similar chemical properties to that of sulfate. The sulfate, usually present in high concentration, hinders adsorption of selenates and decreases the rate of reaction, thereby making the process ineffective for selenium removal. An alternate solution is the application of a pretreatment stage for sulfate ion treatment followed by ion exchange, but this is rarely preferred because it increases the cost of treatment. Overall, physical treatment has found limited application for selenium removal, but physical treatment technologies are still being tested in the laboratory and pilot scale.

3.2. Chemical Treatment

In chemical treatment methods, the physical and chemical properties of dissolved selenium are altered by chemicals, such that it develops a tendency to agglomerate either as a precipitate or a floc. The agglomerated particles are then removed by filtration, flotation, or gravity settling methods. Three principal chemical methods that are favored by the industries for selenium treatment include precipitation, adsorption, and reduction. In the precipitation method, the sulfide ion is used as the most common precipitating agent for selenium removal. Compounds such as sodium dithionite and sodium sulfide are used as a source of sulfide ions in the industry [19]. The typical reaction of selenite by sulfide is given by
H 2 S + SeO 2 SeS 2 + 2 H 2 O
Ferrihydrite adsorption is another prevalent technique in which the contaminants containing selenium are coagulated using ferrous and ferric salts. The ferrous and ferric ions work by altering surface properties, such as the surface charge of the contaminants, resulting in agglomeration of selenium particles to flocs. Both methods are effective for selenite treatment, but they tend to fail for selenates because of their low reactivity. A combination of both methods with reduction can remove the majority of selenate contamination. However, a major disadvantage of most chemical methods when compared to physical methods is the huge amount of chemical usage, and handling of solid waste produced during the operation. A popular reduction method widely tested on a pilot scale is the use of “zero valent iron” (ZVI) for selenate and selenite reduction [20]. ZVI provides a source of ferrous and ferric iron that stays in the system as hydroxides of iron (ferrous and ferric hydroxides) and directly or indirectly reduces selenate and selenite oxyanions to elemental selenium. The iron dissolution and selenium reduction by ferrous ions are represented by the following reactions:
2 Fe + O 2 + 2 H 2 O   2 Fe 2 + + 4 OH
4 Fe 4 + + O 2 + 2 H 2 O 4 Fe 3 + + 4 OH
3 Fe 0   ( solid ) + SeO 4 2 + 8 H +   3 Fe 2 + + Se 0 ( solid ) + 4 H 2 O
2 Fe 0   ( solid ) + SeO 3 2 + 6 H +   2 Fe 2 + + Se 0 ( solid ) + 3 H 2 O
The reduced elemental form of selenium is insoluble and gets cemented onto the solid iron matrix. Zinc is often used as a reducing agent, as a substitute to iron. Other chemical methods, such as electrocoagulation, photoreduction, and catalyzed cementation, have also been tested on a pilot scale, but have not been implemented on an industrial scale. Table 3 provides a list of available techniques, reported in the literature, that have been employed for treatment of wastewater containing selenium contamination.

3.3. Biological Treatment

Biological treatment methods primarily employ sulfate-reducing bacteria (SRB) species (Desulfomicrobium sp.) to treat wastewater containing oxyanions of heavy metals, such as chromium, selenium, and arsenic. The method involves fixing or culturing SRB on an activated carbon bed, which acts as a substrate for their growth (thus forming SRB biofilms), and passing the wastewater through these activated carbon beds laden with SRB biofilms. The SRB, under anaerobic conditions, reduces dissolved selenite and selenate ions to insoluble selenium, thereby precipitating them from the wastewater stream [25,26]. The underlying biochemical conversion is represented by the reactions below [33]:
SeO 4 2 + organic . C   SeO 3 2 + CO 2
SeO 3 2 + organic . C     Se + CO 2 + H 2 O
One of the major factors that affect the process is the surrounding environment, which should be devoid of oxygen (SRB are anaerobic species) and maintained within a fixed temperature range to support bacterial growth. The environment is also affected by other dissolved contaminants in the wastewater, and their specific oxidation-reduction potential (ORP). For example, the presence of nitrates is detrimental to selenate and selenite reduction because the reduction of nitrates occurs at a higher ORP than selenates, thereby causing bacteria to preferentially utilize nitrates. Therefore, a pretreatment stage for nitrates is generally added to the treatment plant to allow effective selenite/selenate reduction.
Biological treatment has been found more effective in treating these oxyanions than other chemical and physical methods. Common variations to this method can be found for agricultural wastewater treatment such as the use of immobilized alginate enzymes, bacterial inoculum treatment, and nitrate-bearing solution treatment. However, the huge amount of sludge generated and its safe disposal are major disadvantages of biological treatment.
Another variation of the biological method is the membrane biofilm reactor, in which hydrogen in its gaseous form is passed through a thin biofilm grown on a permeable membrane (rather than the activated carbon bed). This hydrogen acts as a substrate for bacterial growth and reduction. Autotrophic bacteria are used for the biofilm instead of heterotrophs, which offers an advantage of less sludge production over the previously mentioned method [19]. The underlying chemical reaction is represented below:
SeO 4 2 + 3 H 2 + 2 H +     SeO + 4 H 2 O
This process has also been referred to as the Advanced Biological Metals Removal (ABMet) Process and Hydrogen-based Fluidized Bed Reactor (FBR) system.
Passive biological treatment is another commercially-applied biotreatment technique. Oxidized forms of selenium (selenite and selenate) can be reduced to selenite, elemental selenium, and selenides through microbial reduction, followed by impounding in soil and sediments. Passive biological treatment is designed for vertical and horizontal subsurface flow of water through a reducing organic substrate to achieve microbial and chemical reduction of selenium with shorter residence times and smaller areas than constructed wetlands. Passive treatments offer advantages of low capital, operating, and maintenance costs without external energy inputs or use of chemicals. However, there are some limitations to their application, such as the requirement of a large land area and meeting the acceptable limits for selenium concentrations [2].

4. Overview of Selenium in Alaskan Mines

Alaska has a rich history in mining and is known for its precious metal deposits. Currently, there are six major operating mines in Alaska that produce gold, silver, lead, zinc, and coal with a combined annual production of up to 36 million tons per year [34]. Figure 3 shows the mines that are in production, along with the types of deposits.
The Alaska Department of Environmental Conservation (ADEC) and Alaska Department of Natural Resources (ADNR) are responsible for implementing regulations and monitoring waste discharge from these mines to nearby water streams and to the groundwater. The Alaska Water Quality Standards chronic and acute criteria for selenium are 5 µg/L and 20 µg/L, respectively [35]. As per the report of ADNR and ADEC [36,37,38], most of the operating mines were able to maintain selenium levels within the acceptable limit in their discharge, though minor deviations were observed for Kinross Fort Knox, Teck Red Dog Mine, and Sumitomo Pogo Mine. Each of the mines is summarized below.
Kinross Fort Knox: Located 25 miles northeast of Fairbanks is a mine operated by Kinross Gold Corp. (Toronto, ON, Canada) that consists of two open-pit gold mine complexes—Fort Knox and True North. The Fort Knox orebody is a low-grade gold deposit with an average grade of 0.68 g/ton, hosted in and along the margins of quartz veins, shears, fractures, and pegmatites within a granite intrusion [39]. Gold is associated with anomalously high bismuth and is low in sulfide content. The mined ore is processed on site in a milling facility where the gold is recovered using carbon-in-pulp, heap leach, and gravity separation processes, thereby producing 400,000 ounces of gold annually. The tailings produced during processing are discharged in a Tailings Storage Facility (TSF), which consists of deposited tailings, a decant pond, dam, seepage interception system, and a seepage monitoring system.
Fort Knox monitors the concentration of selenium in the tailings decant and the seepage reclaim. Selenium concentrations were low when ore was mined from the Fort Knox pit, but significantly higher values were measured when True North ore was mined from 2001 to 2004 [39]: concentrations of selenium ranged from 10 to 65 µg/L. After True North production was discontinued in 2004, the concentration showed a downward trend (Figure 4) to a constant mean value of 1 to 2 µg/L.
Pogo Gold Mine: Located 38 miles northeast of Delta Junction in the Goodpaster River Valley is an underground gold mine owned by Sumitomo Metal Mining Co. (Tokyo, Japan). The Pogo deposit is a gold sulfide ore body hosted in a large quartz vein system, with low-grade gold present in quartz stockworks and an average grade of 10 to 12 g/ton. Ore is produced at a rate of up to 2500 tons per day and is processed in a milling facility using flotation, leaching, and gravity separation processes, thereby producing around 400,000 ounces of gold annually.
Tailings produced from the mine are from two sources, flotation and cyanide leaching. The tailings are treated separately; the one free of cyanide is used for dry stacking, while the other is detoxified and used as backfill in the underground mine. Pogo Mine monitors the groundwater, surface water, and effluent discharge for contaminants. The high concentration of selenium in 2000–2001 was due to specific groundwater chemistry that had high concentrations of different toxic elements including selenium. Hence, selenium limits were not exceeded. According to the Pogo Mine annual activity and monitoring report submitted to ADEC [38], high concentrations of selenium were reported from flotation tailings in the year 2013–2014. Typical selenium concentrations for other years were below 3 µg/L. The elevated concentration was because of the trial of using a copper sulfate reagent with high selenium concentration. The selenium concentration returned to acceptable limits after the company transitioned to another reagent [38]. Since the transition to the new reagent was swift and immediate, the temporary exceedances in 2013–2014 did not impact monthly and yearly data and hence are not reflected in Figure 4.
Red Dog Mine: Located 82 miles north of Kotzebue is the world’s largest zinc mine, owned by Teck Resources Ltd. (Vancouver, BC, Canada). The deposit consists of sulfides of zinc, lead, and iron-bearing minerals in a Mississippian formation. Ore mineralogy primarily consists of chalcopyrite, galena, marcasite, pyrite, sphalerite, and quartz, with an average grade of 17% zinc, 4.8% lead and 80 g/t silver [37]. Ore is produced at a rate of up to 9000 tons per day and processed in a milling facility using flotation, thereby producing about 580,000 tons of zinc concentrate annually.
Tailings produced from the mine are discharged in a tailings dam, from which the water is recovered and sent to the water treatment plant (WTP). The WTP uses sodium sulfide and oxygen to precipitate heavy metals as insoluble metal sulfides and hydroxides that are flocculated together and separated by allowing them to settle in a settling tank. The treated water is then checked for dissolved metals and contaminants; if they are within acceptable limits, the water is discharged into Red Dog Creek; otherwise it is recirculated to the tailings dam. The selenium concentration at Red Dog Mine had been a prime concern, as in 1997 it reached an approximate value of 12 µg/L (Figure 4), which exceeded the mandated level of 6 µg/L [39]. The milling and the flotation circuits were surveyed and it was found that flotation reagents (predominantly a cyanide reagent) were responsible for unexpected selenium increases in the tailings stream. Survey results showed enrichment of selenium as selenocyanate (SeCN) at up to 93 µg/L in the lead rougher circuit, which was a point of cyanide addition. However, most of the selenocyanate was oxidized because of the presence of other reagents. The final concentration of selenium reported in the tailings dam and reclaimed water ranged from 4 to 6 µg/L [40]. The unusual decrease in 1998–1999 of selenium concentration in Red Dog Mine was studied by taking samples and conducting simulation studies. It was concluded that the selenium concentration decrease was from precipitation due to the presence of gypsum (CaSO4·H2O) and hematite (Fe2O3) in the tailings impoundment [41]. Another reason was microbial activity (owing to the presence of SRB) at the tailings dam that converted dissolved selenates to selenides.
Several tests for selenium removal were conducted at Red Dog mine: GE advanced metals removal process, electrochemical process (ion-exchange membrane with electrical currents), and RO membrane filtration [39,40,41,42]. A promising method that emerged was in-situ pit lake microbial treatment. Using this technology, it is possible to decrease selenium loading by generating an anaerobic environment through the addition of carbon nutrients [40]. Many of these methods are currently in the pilot testing phase, and eventually, field deployment will demonstrate the actual efficacy and benefit of these techniques.

5. Future Directions

In the past 10 years, biological treatment has emerged as one of the preferred techniques for selenium treatment. It offers a low-cost alternative to more expensive chemical and physical selenium removal methods. Furthermore, it has the proven ability to reduce selenium concentrations to levels acceptable by different environmental regulatory agencies. Both active and passive biological systems have been developed in the past few years. Biochemical and in-situ microbial reduction appear to be treatment processes suited for cold climatic regions, although work is needed to characterize the efficacy of these biological approaches in colder environments. Also, more fundamental work is needed to understand the role of SRB and biological treatments in reducing selenium levels at the Red Dog Mine.

6. Conclusions

This paper discussed the key aspects related to selenium contamination, environmental impacts of selenium release, and an overview of extant technologies used for removal of selenium in industrial and mining settings; both traditional and novel methods were reviewed. The efficiency of selenium removal depends on the characteristics of the source or the waste to be treated. One of the up-and-coming and promising methods for selenium removal is the biological treatment that is both technologically feasible and economically efficient in meeting the mandated selenium levels. However, selection of any treatment process is very context and site-specific, depending on the required reduction from existing levels, as well as resource needs and resource availability at the site.
Additionally, this paper discussed and reviewed selenium issues at Alaskan mines and discharge sites. Some of the mines reported higher selenium in their discharge waters in early years (earlier than 2006), primarily due to the enrichment of selenium during processing of other metals. Red Dog Mine has been considered a significant source of selenium release; however, a potential water management system using precipitation and flocculation methods to control selenium levels is being evaluated. The unusual decrease in selenium concentrations at Red Dog Mine, owing to the presence of SRB and gypsum in tailings, opens a new area of study to allow selenium treatment methods to be applied and duplicated at a commercial scale. Overall, continued research in selenium removal technologies will provide tools to the industries to successfully develop and expand economic initiatives while also allaying any environmental concerns in a cost-effective manner.

Acknowledgments

The authors wish to acknowledge support from the University of Alaska Fairbanks and the Alaska Department of Environmental Conservation for access to data used in this manuscript. Additionally, author Srijan Aggarwal acknowledges support from the Alaska EPSCoR NSF award #OIA-1208927 and the state of Alaska.

Author Contributions

T.G., G.A., S.A. and R.G. conceived and designed the study; A.K. and V.S. conducted the study; A.K., T.G., G.A. and S.A. analyzed the data; all authors wrote the paper.

Conflicts of Interest

The authors declare no conflict of interest.

Abbreviations

The following abbreviations are used in this manuscript:
ABMetThe Advanced Biological Metals Removal Process
ADECAlaska Department of Environmental Conservation
ADNRAlaska Department of Natural Resources
EPAEnvironmental Protection Agency
FBRFluidized Bed Reactor
MCLMaximum contaminant level
ROReverse Osmosis
ZVIZero-Valent iron

References

  1. Lemly, A.D. Aquatic selenium pollution is a global environmental safety issue. Ecotoxicol. Environ. Saf. 2004, 59, 44–56. [Google Scholar] [CrossRef]
  2. Sandy, T.; DiSante, C. Review of Available Technologies for the Removal of Selenium from Water; Technical Report; CH2M Hill: Englewood, CO, USA, June 2010; pp. 2–223. [Google Scholar]
  3. Sharma, V.K.; McDonald, T.J.; Sohn, M.; Anquandah, G.A.K.; Pettine, M.; Zboril, R. Biogeochemistry of selenium. A review. Environ. Chem. Lett. 2014, 13, 49–58. [Google Scholar] [CrossRef]
  4. Brookins, D.G. Eh-pH Diagrams for Geochemistry; Springer: Berling/Heidelberg, Germany, 1989; Volume 53, pp. 18–19. [Google Scholar]
  5. Watanabe, T.; Kiron, V.; Satoh, S. Trace minerals in fish nutrition. Aquaculture 1997, 151, 185–207. [Google Scholar] [CrossRef]
  6. Lemly, A.D. A teratogenic deformity index for evaluating impacts of selenium on fish populations. Ecotoxicol. Environ. Saf. 1997, 37, 259–266. [Google Scholar] [CrossRef] [PubMed]
  7. Sappington, K.G. Development of aquatic life criteria for selenium: A regulatory perspective on critical issues and research needs. Aquat. Toxicol. 2002, 57, 101–113. [Google Scholar] [CrossRef]
  8. U.S. Energy Information Administration (EIA). Annual Coal Report 2015; Technical Report; U.S. Department of Energy: Washington, D.C., USA, November, 2016; p. 69.
  9. Seshadri, P.; Sisk, D.; Bowman, F.; Benson, S. Leachability of Arsenic and Selenium in Submicron Coal Fly Ash. In Proceedings of the World of Coal Ash Conference, University of Kentucky and American Coal Ash Association, Denver, CO, USA, 9–12 May 2011.
  10. Izquierdo, M.; Querol, X. Leaching behavior of elements from coal combustion fly ash: An overview. Int. J. Coal Geol. 2012, 94, 54–66. [Google Scholar] [CrossRef][Green Version]
  11. Yan, Q.Z.; Zhang, J. Species and distribution of inorganic selenium in the Bohai Sea. Chin. J. Oceanol. Limnol. 2006, 24, 204–211. [Google Scholar]
  12. Nriagu, J.O.; Wong, H.K. Selenium pollution of lakes near the smelters at Sudbury, Ontario. Nature 1983, 301, 55–57. [Google Scholar] [CrossRef]
  13. Wasewar, K.L.; Prasad, B.; Gulipalli, S. Removal of selenium by adsorption onto granular activated carbon (GAC) and powdered activated carbon (PAC). CLEAN Soil Air Water 2009, 37, 872–883. [Google Scholar] [CrossRef]
  14. Mar Systems. Sorbster Removes Selenium from Coal Mine Tailings and Process Waters; Technical Report; Mar Systems: Solon, OH, USA, June 2012; pp. 1–5. [Google Scholar]
  15. Twidwell, L.G.; Mccloskey, J.; Joyce, H.; Dahlgren, E.; Hadden, A. Removal of Selenium Oxyanions from Mine Waters Utilizing Elemental Iron and Galvanically Coupled Metals. In Proceedings of the Jan D. Mill Symposium—Innovations in Natural Resource, Salt Lake City, UT, USA, 28 February–2 March 2005; pp. 299–313.
  16. Desborough, G.; DeWitt, E.; Jones, J. Preliminary Mineralogical and Chemical Studies Related to the Potential Mobility of Selenium and Associated Elements in Phosphoria Formation Strata, Southeastern Idaho; Open-File Report 99-129; U.S. Department of the Interior, U.S. Geological Survey: Reston, VA, USA, 1999; pp. 6–7.
  17. Wen, H.; Carignan, J. Reviews on atmospheric selenium: Emissions, speciation, and fate. Atmos. Environ. 2007, 41, 7151–7165. [Google Scholar] [CrossRef]
  18. Golder Associates. Literature Review of Treatment Technologies to Remove Selenium from Mining-Influenced Water; Technical Report; Golder Associates: Lakewood, CO, USA, July 2009; p. 40. [Google Scholar]
  19. Rittmann, B.E. The Membrane Biofilm Reactor is a Versatile Platform for Water and Wastewater Treatment. Environ. Eng. Res. 2007, 12, 8–11. [Google Scholar] [CrossRef]
  20. Tang, C.; Huang, Y.H.; Zeng, H.; Zhang, Z. Reductive removal of selenate by zero-valent iron: The roles of aqueous Fe2+ and corrosion products, and selenate removal mechanisms. Water Res. 2014, 67, 166–174. [Google Scholar] [CrossRef] [PubMed]
  21. Microbial Technologies Inc. Evaluation of Treatment Options to Reduce Water-Borne Selenium at Coal Mines in West-Central Alberta; Technical Report; Microbial Technologies Inc.: Ochelata, OK, USA, 2005; p. 11. Available online: http://www3.gov.ab.ca/env/info/infocentre/publist.cfm (accessed on 22 September 2016).
  22. Twidwell, L.G.; Mccloskey, J.; Miranda, P.; Gale, M. Technologies and potential technologies for removing selenium from process and mine wastewater. In Proceedings of the Recycling, Waste, Treatment and Clean Technology (REWAS), San Sebastian, Spain, 5–9 September 1999; pp. 1645–1656.
  23. Kharaka, Y.K.; Ambats, G.; Presser, T.S.; Davis, R.A. Removal of selenium from contaminated agricultural drainage water by nanofiltration membranes. Appl. Geochem. 1996, 11, 797–802. [Google Scholar] [CrossRef]
  24. MSE Technology Applications Inc. Selenium Treatment/Removal Alternatives Demonstration Project: Mine Waste Technology Program Activity III, Project 20; Technical Report; MSE Technology Applications Inc.: Butte, MT, USA, June 2001; pp. 1–133. [Google Scholar]
  25. Drelich, J.; Hwang, J.Y.; Adams, J.; Nagaraj, D.R. Proceeding of the Water in Mineral Processing; Society for Mining, Metallurgy & Exploration (SME): Englewood, CO, USA, 2012; pp. 291–294. [Google Scholar]
  26. Manceau, A.; Gallup, D.L. Removal of selenocyanate in water by precipitation: Characterization of copper-selenium precipitate by X-ray diffraction, infrared, and X-ray absorption spectroscopy. Environ. Sci. Technol. 1997, 31, 968–976. [Google Scholar] [CrossRef]
  27. Mavrov, V.; Stamenov, S.; Todorova, E.; Chmiel, H.; Erwe, T. New hybrid electrocoagulation membrane process for removing selenium from industrial wastewater. Desalination 2006, 201, 290–296. [Google Scholar] [CrossRef]
  28. CH2M Hill. NAMC White Paper Report Addendum Selenium Treatment; Technical addendum; CH2M Hill: Englewood, CO, USA, 29 March 2013; pp. 1–68. [Google Scholar]
  29. Frisch, S.; Technologies, E.; Enegess, D.; Technologies, E. Advances in fluidized bed reactor treatment of selenium in mining waters. In Proceedings of the SME Annual Meeting 2014, Salt Lake City, UT, USA, 23–26 February 2014; pp. 1–6.
  30. Quinn, N.W.T.; Leighton, T.; Lundquist, T.J.; Green, F.B.; Zárate, M.A.; Oswald, W.J. Algal-Bacterial treatment facility removes selenium from drainage water. Calif. Agric. 2008, 54, 50–56. [Google Scholar] [CrossRef]
  31. Cohen, R.R.H. Use of microbes for cost reduction of metal removal from metals and mining industry waste streams. J. Clean. Prod. 2006, 14, 1146–1157. [Google Scholar] [CrossRef]
  32. Harrison, T.; Hill, C.H.M.; Sandy, T.; Hill, C.H.M.; Leber, K.; Hill, C.H.M.; Srinivasan, R.; Hill, C.H.M.; Mchale, J.; Corp, P.C. Characterization and treatment of selenium in water discharged from surface coal mining operations in West Virginia. In Proceedings of the Society for Mining, Metallurgy & Exploration (SME) Annual Meeting, Phoenix, AZ, USA, 28 February–3 March 2010; pp. 1–5.
  33. Sonstegard, J.; Pickett, T.; Harwood, J.; Johnson, D. Full-Scale Operation of GE ABMet® Biological Technology for the Removal of Selenium from FGD Wastewaters. In Proceedings of the 69th Annual International Water Conference, San Antonio, TX, USA, 26–30 October 2008; pp. 343–356.
  34. Department of Commerce, Community, and Economic Development. Available online: https://www.commerce.alaska.gov/web/ded/DEV/MineralsDevelopment/MineralsProduction.aspx (accessed on 6 October 2016).
  35. Department of Environmental Conservation. Water Quality Standards. 2016. Available online: http://dec.alaska.gov/Water/wqsar/wqs/index.htm (accessed on 10 October 2016). [Google Scholar]
  36. Kinross. Kinross Fort Knox Annual Activity Report 2015. Available online: http://dnr.alaska.gov/mlw/mining/largemine/fortknox/annualmeetings.cfm (accessed on 15 October 2016).
  37. Sumitomo Metal Mining Pogo LLC. 2015 Annual Activity and Monitoring Report Sumitomo Metal Mining Pogo LLC. Available online: http://dnr.alaska.gov/mlw/mining/largemine/pogo/ (accessed on 15 October 2016).
  38. 2015Teck Resources Limited. Teck 2014 Annual Report. Available online: http://dnr.alaska.gov/mlw/mining/largemine/reddog/ (accessed on 18 October 2016).
  39. Fort Knox Mine. Available online: http://northern.org/programs/clean-water-mines/hardrock-mines-in-interior-and-arctic-alaska/fort-knox-true-north-mine-1 (accessed on 15 October 2016).
  40. Edgerton, D. Reconstruction of the Red Dog Zn-Pb-Ba orebody, Alaska: Implications for the vent environment during the mineralizing event. Can. J. Earth Sci. 1997, 34, 1581–1602. [Google Scholar] [CrossRef]
  41. Edwards, M.; Kulas, J.E.; Kuit, W.J.; Weakly, J.O.; Bloom, N.S.; Wallschlager, D. Aquatic selenium at Cominco’s Red Dog Mine: Sources, speciation, distribution, and control. In Proceedings of the Tailings and Mine Waste ’99, Fort Collins, CO, USA, 24–27 January 1999; pp. 535–542.
  42. Brienne, S.; Falutsu, M.; Weakley, J.; Kulas, J.; Kuit, W.; Geist, D.; Gustafson, J.; Wood, S.; Baker, L.; Rosenzweig, R.; et al. Selenium release and removal from the Red Dog Mine operation. In Proceedings of the British Columbia Mine Reclamation Symposium, Williams Lake, BC, Canada, 18–21 September 2000; pp. 194–203.
Figure 1. Eh-pH diagram for the Se–O–H system [4].
Figure 1. Eh-pH diagram for the Se–O–H system [4].
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Figure 2. Schematic showing selenium cycling in the environment from mining.
Figure 2. Schematic showing selenium cycling in the environment from mining.
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Figure 3. Map showing the location of different mine sites in Alaska and the respective deposits [34].
Figure 3. Map showing the location of different mine sites in Alaska and the respective deposits [34].
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Figure 4. Mean selenium concentrations at Alaskan mines (Pogo Mine, Fort Knox, and Red Dog Mine) from 1998 to 2015. Error bars represent the concentration ranges. Fort Knox mine data from 2001–2004 includes two pits—Fort Knox pit and True North pit.
Figure 4. Mean selenium concentrations at Alaskan mines (Pogo Mine, Fort Knox, and Red Dog Mine) from 1998 to 2015. Error bars represent the concentration ranges. Fort Knox mine data from 2001–2004 includes two pits—Fort Knox pit and True North pit.
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Table 1. US Environmental Protection Agency (EPA) 2016 Aquatic life criteria for selenium.
Table 1. US Environmental Protection Agency (EPA) 2016 Aquatic life criteria for selenium.
Criteria VersionEgg-Ovary (mg/kg dw a)Whole Body (mg/kg dw a)Muscle (mg/kg dw a)Water Lentic (µg/L)Water Lotic (µg/L)
201615.18.511.31.5 (30 day)3.1 (30 day)
a dw: “dry weight” basis.
Table 2. Concentration of selenium in different materials.
Table 2. Concentration of selenium in different materials.
Material or WasteSe ConcentrationReferences
Surface waters0.2 µg/L[1]
Agricultural drainage water140–1400 µg/L[11]
Copper ore20–82 µg/g[12]
Mining wastewater3–12 µg/L[13]
Coal0.4–24 µg/g[12]
Coal mining pond water8.8–389 µg/L[14]
Gold mine wastewater0.2–33 µg/L[15]
Uranium mine wastewater1600 µg/L[15]
Oil shale1.3–5.2 µg/g[1]
Crude shale oils92–540 µg/L[1]
Crude oil500–2200 µg/L[1]
Refined oils5–258 µg/L[1]
Oil refinery wastewater15–75 µg/L[1]
Phosphate ore2–20 µg/g[16]
Table 3. Overview of selenium removal technologies reported in the literature.
Table 3. Overview of selenium removal technologies reported in the literature.
CategoryTreatment Technology Test ScaleTreatment PerformanceLocation of TestReferences
PhysicalReverse osmosisFull scaleEffective levels below 5 µg/L; Reduced concentration from 12–22 µg/L to 2 µg/LBarrick’s Richmond Hill Mine, SD, USA[21]
Activated Alumina AdsorptionLab ScaleSelenium was adsorbed over pH range 3–7 for concentrations of 100–200 µg/LMunicipal Environmental Research Lab, OH, USA[22]
NanofiltrationLab and field scaleUp to 95% selenium removal from highly contaminated agricultural drainage (up to 1000 µg/L)Los Banos, California, USA (Lab scale), Kennecott South, UT, USA (Field Scale)[23]
Ferrihydrite adsorptionFull scaleReduction from 1950 µg/L to 90 µg/LKUCC Garfield Wetlands-Kessler Springs, UT, USA[24]
Ion-exchange (physicochemical)Lab scaleReduction from 1 g/L to 0.1 mg/LKennecott Mining Company, Boyle Engineering Corp, USA[18]
ChemicalPrecipitationFull scaleReduction from 0.213 mg/L to 0.014 mg/LCameco’s Key Lake Operation, Canada[25]
Cupric co-precipitationLab scalePrecipitation of Selenocyanate from petroleum refinery processUniversity of Grenoble, France and Unocal Corporation, CA, USA[26]
ElectrocoagulationLab scaleReduction from 2.32 mg/L to 0.03 mg/LUniversity of Mining and Geology, Bulgaria and Saarland University, Germany[27]
Zero- valent ironFull scaleReduction of influent selenium drop from 19 to 4.7 µg/LWest Virginia coal mines, Phosphate mine in Idaho, USA[28]
Fixed bed adsorptionPilot scale and full scaleReduction from 0.07–0.86 mg/L to 1–11 µg/LCameco Resources Smith Ranch-Highland operation, WY, USA[29]
CementationLab scaleReduction from 1950 µg/L to below 5 µg/LUniversity of Montana, MT, USA[24]
BiologicalAlgal-bacterialLab scaleReduction from 300–500 ppb to 0–100 ppbUniversity of California, Berkeley, USA[30]
Algal volatilizationLab scaleApproximately reduction by 23%University of California, Riverside, USA[30]
Microbial reductionFull scaleReduction from 70 µg/L to 4.6 µg/LGolder, Closed mine in South Dakota, USA[31]
Fluidized bed reactor treatmentPilot scaleAchieved less than 4.7 µg/L in effluentWest Virginia, USA[32]
ABMetPilot scale and full scaleReduction from 20–300 µg/L (influent Selenium) to 0.7–2.0 µg/L (effluent Selenium)British Columbia, Canada (pilot scale), West Virginia, USA (full scale)[28]
Biochemical reactorFull scaleInlet concentrations of 180 µg/L decreased to effluent concentrations from 3 to 33 µg/LAlberta, Canada[18]
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