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Geosynthetics 

 
Authors: Jack Caldwell and Ed Kavazanjian, Jr.

Revised: January 2012

Summary

This review describe the the current state of technology of geosynthetic materials used at mine sites. Topics covered include regulations, design guidance, issues in the use of geosynthetics in mining, and geosynthetics fo uranium wastes.

INTRODUCTION

Geosynthetics may be used at mines during operation in liners for surface water ponds (including storm-water, non-storm-water, and sediment ponds), process solution ponds (including pregnant or barren solution ponds and recycle ponds), heap leach pads, waste rock dumps, and tailings impoundments. Geosynthetics may be used at mines at closure in the covers of heap leach pads, waste rock dumps, and tailings impoundments.

Geosynthetics are used in mine facilities to limit infiltration of gas and water to the closed waste facilities, control seepage of water and potentially contaminating constituents from the operating and closed waste facilities, and provide for drainage of liquids from the operating and closed facilities.

Lupo and Morrison in Innovative Geosynthetic Liner Design Approaches and Construction in the Mining Industry list these mining-related uses of various geosynthetics:

  • Geomembrane
    • Process solution pond liners
    • Heap leach facility liner systems
    • Tailings impoundment liner system
    • Encapsulation of waste rock to mitigate acid mine drainage.
  • Geosynthetic Clay Layer (GCL)
    • Encapsulation of waste rock to mitigate acid mine drainage
    • Barrier layer below geomembrane liner.
  • Geotextile
    • Filter layer for underdrains and collection pipes
    • Cushion layers over geomembrane liners
    • Ground stabilization
    • Erosion Control.
  • Geogrid
    • Ground stabilization
    • Remediation of mine workings
  • Plastic Pipe
    • Process solution collection and conveyance
    • Solution recovery
    • Leak detection and monitoring.

Issues in the use of geosynthetics in mine facilities include durability, strength, deformation resistance, response to the chemicals in the mine waste facilities, and, in the case of drainage, clogging. Each of these is discussed in this paper.


Landfill-Related Information Sources

Websites and e-publications from the landfill industry contain considerable information of interest to the mine and miner charged with selecting and installing a liner beneath a mine facility. The Geosynthetic Institute provides information on the use of liners in landfills. Here are some sites where the liner requirements are set out by state agencies:

This paper on the use of a host of geosynthetic products offers a number of examples of how geosynthetic products can offer replacements to natural materials in achieving "functions such as filtration, drainage separation and reinforcement requirements" in landfills. This document by the International Geosynthetics Society (IGS), further illustrates the extent of the uses of geosynthetics in landfills today.

Regulations

The Nevada State Regulations for mine closure include requirements to use liners in specified instances.

The Ontario Department of Environmental Quality requires that new heap leach pads and mine pits that contain water at closure should be lined.

The Arizona Mining Guidance Manual (BADCT)

General

The Arizona Mining Guidance Manual BADCT (Manual) discusses best available demonstrated control technologies, including the use of geosynthetics in the design, construction, operation, and closure of mining facilities such as ponds, heap leach pads, and tailings impoundments. Appendix C discusses the use of compacted clay liners and geosynthetics liners in heap leach pads set out guidance for the selection of liners for mine facilities. Appendix D sets out Quality Control and Quality Assurance requirements for installation of liners in mining facilities.

The Manual requires as a minimum the following for liners used in mine facilities: "Geomembrane material and thickness should be selected to resist chemical reaction and ultraviolet radiation. The liner should provide retention of tensile strength and maintenance of low permeability with time. The facility design should specify a liner of appropriate mechanical strength to maintain integrity of the liner system during the design life of the facility. It the expected liner life is shorter than the design life of the facility, appropriate liner replacement, repair, or other contingency plans must be included."

In the following subsections there are brief descriptions of the use of geosynthetics in mine facilities and a summary of some of the Manuals requirements for the use of geosynthetics in such mine facilities.

Surface Water Ponds

The Manual states that non-storm water ponds shall be designed with a single geomembrane with a thickness of 30 mil (60 mil for HDPE) and that selection of the geomembrane shall consider chemical compatibility, the depth of fluid to be sotred, and foundation conditions. Geomembranes exposed to the sun must be certified UV resistant. Geomembranes are required to be secured in an anchor trench.

Process Water Ponds

The Manual states that process water ponds shall be designed with a double liner system and leack collection and removal system (LCRS) between the two liners. The lower liner must be a composite including a geomembrane with a thickness of 30 mil (60 mil for HDPE) underlain by at least six inches of compacted soil (3/8 inch minus native or natural material) with an hydraulic conductivity no greater than 10-6 cm/sec. Selection of the geomembrane shall consider chemical compatibility, the depth of fluid to be sotred, and foundation conditions. Geomembranes exposed to the sun must be certified UV resistant. Geomembranes are required to be secured in an anchor trench.

The LCRS must be designed to minimize the head on the lower liner and to collect and remove fluids from between the upper and lower liner. The LCRS should consist of a layer of sand, geonet, or other permeable material that achieves a flow capacity equivalent to a 1-foot thick layer with an hydraulic conductivity of 10-2 cm/sec or greater and an inclination of at least 3 percent.

Heap Leach Piles

Liners are required beneath heap leach piles in order to preclude loss of leachate that must be directed to outlet points for collection and ore extraction. Lupo in a paper Heap Leach Facility Liner Design describes the use of geosynthetics as liners in heap leach pad construction and operation. Thiel and Smith in State of Practice Review of Heap Leach Pad Design Issues list thirteen mines in South American where geomembranes have been used in the liners of heap leach pads. In most cases a 60 or 80 mil HDPE was used. Thiel in particular has written extensively on geomembranes in use at mines.

M. O. Defillippis in Geomembranes used in heap Leach SX-EW Mining: a Manufacturer's Perspective writes of practice in Chile regarding the use of geomembranes in heap leaching.

The Manual notes that in the 1970s a number of heap leach pads were constructed using polyvinyl chloride (PVC) liners; the use of high density polyethylene (HDPE) became more common in the 1980s for both heap leach pads and tailings impoundments; in the late 1980s, very low density polyethylene (VLDPE) was used in heap leach pads and tailings impoundments.

This Manual states that the BADCT for the liner of a heap leach pad (or a tailings impoundment) is a geomembrane at least 30 mils thick (60 mils for HDPE) underlain by at least 12 inches of soil compacted to an hydraulic conductivity of no greater than 10-6 cm/sec. An engineering equivalent to this is a double geomembrane liner with sand of a geosynthetic leachate control and recovery system (LCRS).

The manual requires that the geomembrane be covered by a protective drainage layer consisting of ¾ inch minus well draining material with a minimum thickness of18 inches, and corrugated, perforated HDPE pipe of at least 3-inch diameter placed every 20 ft.

The Manual provides that geologic features such as low permeability sediments, may be considered BADCT if it can be shown that "effect discharge reduction prior to reaching the water table." Additional geologic containment may be demonstrated by showing that pollutants will be attenuated in the vadose zone.

At closure of a heap leach facility, the Manual requires measures be taken to limit leachate production. Control technologies listed include: surface grading to enhance runoff; vegetation to promote moisture removal; and covers that may include low permeability geosynthetics to limit infiltration.

Tailings Impoundments

The U.S. Environmental Protection Agency's (EPA) 1997 report "The Feasibility of Lining Tailings Impoundments" summarizes a series of reports that evaluate the design and installation of tailings impoundments at hard rock mines. The EPA report concludes that the size of land-based mining units, the character of mining wastes, and technical factors do not necessarily preclude the use of liners or leachate collection systems.

The Manual notes "A few unlined [tailings] facilities have performed satisfactorily where a low permeability foundation, deep water table and a high degree of hydrologic isolation were present. Absence the presence of an adequate 'geologic liner' generally accepted practice has been to employ artificial liners." The Manual states that BADCT for lining of tailings impoundments is a geomembrane at least 30 mils thick (60 mils for HDPE) underlain by at least 12 inches of soil compacted to an hydraulic conductivity of no greater than 10-6 cm/sec. The manual also mandates a protective/drainage layer consisting of ¾ inch minus well draining material with a minimum thickness of18 inches, and corrugated, perforated HDPE pipe of at least 3-inch diameter placed every 20 ft. Furthermore the tailings are to be placed to cover the protective/drainage layer in such a way that after deposition of a continuous layer of tailings, the rate of infiltration into the protective/drainage layer and the flow capacity thereof must be such as to limit the average and maximum head over the liner to less than two and less than five feet respectively. Deformation of the impoundment affecting the geomembrane shall be less than 6 inches. At closure a cover that limits infiltration must be provided.

Waste Rock Dumps

We are not aware of any waste rock dumps where liners have been installed. Any such liner would have to be able to withstand the impact of waste dumping and the large size of the rock that could tear the liner.

It is conceivable that the need to control acid seepage would make a liner an attractive option at a rock dump. Any such facility would have to be designed to deal with the long-term seepage that would then appear at the outlet from the dump and which would have to be treated indefinitely.

Many mine waste dumps contain sulphidic minerals that generate acidic drainage when they oxidize in the presence of oxygen and percolating water. Oxygen may enter the dump via one or more of these mechanisms: gas-phase diffusion; gas-phase advection; liquid diffusion; liquid advection. Covers for waste rock dumps to control gas migration into the dump are discussed by Kim and Benson in a paper entitled Contributions of advective and diffusive oxygen transport through multilayer composite caps over mine waste. They formulate analytical and numeric techniques to study oxygen transport through multilayer composite (MLC) caps that are defined as caps consisting of earthern and geosynthetic (polymeric) components where the primary barrier to oxygen transport is a geomembrane (1 to 2 mm thick polymeric sheet) overlying a clay layer or GCL. They show that the gas-phase diffusive flux typically comprises 99 percent of the total oxygen flux through a MLC cover and hence they recommend that designers "focus on design elements that features that will limit diffusion of gas-phase oxygen."

Use of Geosynthetics in Mining

Basal Liners

The primary use of geosynthetics in mining are as basal liners for heap leach and liquid containment facilities. These geomembrane liners have been used for the past 40 years in the industry. Presented at the International Geosynthetics Society in 2006, the paper titled An Overview of geomembrane history in the mining industry gives a recount of the histories of the uses of geomambrane in the industry in the past 35 years. They also look foward and examine the emerging issues that will need to be dealt with in the not so distant future.

Soil Reinforcement

In Mining, geosynthetics are also used in many areas of construction such as embankments for roads and slopes stabilisation. For a general overview of the geosynthetic terminology used in soil reiforcement, this piece collates a number of the interaction terms. This paper examines the impact of mining (subsidence) on an old transport viaduct and the soil reinforcement technology that was used in the replacement transport link.

Dewatering Applications

The previous catagories in this section are well known and have many publications. However, there are other applications of geosynthetics in the mining industry, one fascinating example of this is the use of large geosynthetic containers for dewatering purposes. The presentation by Mike Watts shows us an innovative method for using geosynthetics to dewater a slurry by-product of coal washing. In this case the "Geotube" bags were filled with the slurry, and the water was filtered out through the porous geosynthetic.

Wick Drains are a more common use of geosynthetics in a dewatering capacity in order to stabilise tailings so that the area they occupy can be reclaimed. Reclamation generally infers the placing of a cover over the tailings in order to achieve a number of goals, as this paper on the use of Wick Drains points out:

  • Protection from water erosion
  • Protection from wind erosion
  • A growth media for revegetation
  • A capillary break to prevent the uptake of metals by vegetation
  • An impermeable barrier to limit infiltration into the deposit
  • A barrier to limit the diffusion of gases such as radon and oxygen
  • To my knowledge, the most recent publication in the area of Wick Drains concerns their installation in Suncor's Pond 5 reclamation project. Here testing was conducted on vertical Wick Drains to prove their potential in accelerating the dewatering of fine tailings. The Paper takes us throught the full testing plan including the laboratory clogging experiments, field testing, and Fast Lagragian Ananysis of Continua (FLAC) used to predict the dewatering period.

    Design Guidance for Mine Facilities Including Geosynthetics

    Void Protection

    Lupo and Morrison in Innovative Geosynthetic Liner Design Approaches and Construction in the Mining Industry describe the use of geosynthetics in stabilizing the foundations of facilities at mines. In particular, they note that geomembranes have been used where waste rock dumps and tailings are placed over old mine workings. If the location of the shaft or potential sinkhole is known, a geomembrane may be placed over a pile of sacrificial soil. When the void develops beneath the pile, the soil will "flow" into the void and the geomembrane settle, but generally remain intact to control seepage from the tailings to the void.

    Access Roads

    Douglas in Repeat-load Behavior of Geosythetic-built Unbound Roads states that in 1996 the resource industries in Canada (mining, forestry, and energy) built 6,100 km of roads over poor subgrades. Yet the roads must be capable of carrying heavy loads. The author describes methods for testing geosynthetics for and using geosynthetics in such roads.


    Issues in the Use of Geosynthetics in Mining

    Durability

    Kavazanjian et al. in Geosynthetic Barriers for Environmental Protection at Landfills collate and summarize the evidence that establishes that geocomposite liners systems at landfills when well designed and constructed, leak at such a slow rate that the impact, if any, on the environment is negligible, at least in the short and intermediate term. The authors present evidence that the performance life of the primary geomembrane in these liners may be as long as 100 to 200 years at landfill temperatures on the order of 20 deg. C but may be as little as 50 years at elevated temperatures found in some landfills (e.g. 35 deg. C). (Geomembrane service life is primarily a function of temperature and the chemical concentration of the leachate to which it is exposed.) The authors also present evidence that geosynthetic clay liners (GCLs) are as effective as compacted clay layers as the underlying component of a composite liner system. The authors note that the service life of an exposed HDPE membrane may be 50 years or more under typical conditions.

    The authors present evidence that GCLs in capping systems can be effective despite concerns over durability. For example they note that the service life of a GCL in a capping or liner system may be hundreds to thousands of years from an hydraulic conductivity perspective, although the durability of the fibers may limit the durability of reinforced GCLs placed on slopes to less than a hundred years from the strength perspective.

    In particular, with regard to desiccation-induced damage to a GCL in a cover system, the authors recommend either placing the GCL beneath a sufficient thickness of soil to keep the GCL below the "active" zone of soil where significant drying may occur where possible and under at least 0.6 to 1 m of soil overburden so that self-healing may occur. Cation exchange in the GCL may convert the sodium bentonite to calcium bentonite and cause increases in the hydraulic conductivity of the GCL. However, the GCL will still have a very low hydraulic conductivity after cation exchange. Contact with chemical may also affect the hydraulic conductivity of a GCL. Prewetting, higher stresses, and careful testing of chemical compatibility are recommended to mitigate the effects of cation exchange and chemical incompatibility.

    Further studies into the longevity of geosynthetics were undertaken for the Conference on Geosynthetics, Brazil, 2010, where the "Needs are identified for improved testing techniques and associated performance criteria that are specific to the mining industry".

    Response to Placement of Overlying Materials

    Crouse et al. in Geomembrane and GCL Mining Usage Tests describe construction of test pads to establish the impact of placement details on the condition and strength of a geomembrane and a GCL. In the first test pad, constructed to simulate placement of a liner on the upstream face of an embankment for mine tailings, the following layers (from bottom to top) were placed: alluvial/colluvial bedding; 14 oz/sy geotextile; 60il HDPE; geonet; 80 mil HDPE; and 6 oz/sy geotextile. An 80 tonne truck was parked overnight of this layers system to simulate the loading from the tailings. The next day samples of the liner, the 60 mil HDPE were cut, examined and trenght tested. No impact on the integrity of the HDPE and no reduction of strength was noted.

    The second test pad was constructed to replicate placement of a cover over a the sideslopes of a tailings impoundment in Colorado. The actual sideslopes vary from 2:1 to 3:1. The following layers (from bottom to top) were placed on a 3:1 slope: regraded tailings; GCL; geocomposite drainage layer (geonet between two 7 oz/sy geotextiles); 18-inch thick rock cover of minus 4 inch material. After construction, the geosynthetics were exhumed and visually examined. Based on the observations that there was no significant dames, the test pad construction procedure was approved for full=scale implementation.

    Geomembrane Puncture

    Thiel and Smith in State of Practice Review of Heap Leach Pad Design Issues note that generally the geomembrane in a heap leach pad is a 1.5 mm polyethylene (HDPE of LLDPE), that the overlying material is generally minus 25 to 38 mm in size, and that overburden loads may exceed 2,000 kPa, yet "it is almost unknown for a cushion fabric to be used to protect the geomembrane." The authors justify this practice on the basis of: cost; the detrimental impact of a cushion on stability; and the inherent lack of vulnerable groundwater resources at the sites where geomembrane protection is not provided.

    Response to Leachate

    Gulec and Benson in Effects of Acidic Mine Drainage on the Mechanical and Hydraulic Properties of Three Geosynthetics describe testing a geomembrane, geotextile, and geocomposite by immersing them in a synthetic acid mine drainage fluid to quantify the impact of the fluid on the mechanical properties of the geosythetics. They note that none of the mechnical or hydraulic properties showed statistically significant variation regardless of the fluid properties, temperature, or immersion duration.

    Thiel and Smith in State of Practice Review of Heap Leach Pad Design Issues described the effect of sulphuric acid to extract copper from heap leach pads and tailings on geomembranes. They report observed loss of strength of HDPE and VLDPE at mines in South America.

    Attenuation

    Lange, Rowe, and Jamison in Investigation of Geosynthetic Clay Liners to Contain Metals in Mining Leach report that a GCL permeated with leachates representative of acid mine drainage and the leachate from a gold mine tailings showed large attenuation of the metals and metalloids in the leachates. Specifically, they report: (a) metals from the acid mine drainage, including Fe, Zn, Mn, As, Pb and Al were retained by the clay (b) the gold mine leachate showed gypsum precipitate as well as SO4 and Ca and metals such as As and Cd retention.

    Clogging

    Rowe notes that these mechanism lead to clogging of geosynthetics in landfills:

    • Retention (from the passing leachate onto the medium) of biomass and suspended solids.
    • Fermentation of volatile fatty acids by biomass attached to the medium suspended biomass.
    • Precipitation of ions (predominantly as CaCO3).

    Landfill leachate differs substantially from the leachate of mine facilities. However it is known that clogging of conventional geotechnical filters and drains in mine facilities clog. It seems reasonable, therefore, to conclude that geosynthetic drains and filter media will clog due to the same site-specific factors-generally chemical and biological precipitation and growth.

    Acid Rock Drainage

    Basal liners for heap leach and liquid containment are a major element in the control of Acid Rock Drainage (ARD). In these instances, geosynthetics are used in lining and also to cut off the ARD drivers e.g.water and oxygen. The paper Why Are We Still Struggling with Acid Rock Drainage? from the InfoMine Library illustrates the problems with designing effective surface impoundments:

    (i) Time scales for mine life cycles,testing, field observation, and evaluation;

    (ii) Physical scale up from small scale testing to field scale application;

    (iii) A high reliance on conceptual and numerical models; and finally

    (iv) A general lack of full scale, longer-term (i.e. several decades) performance data to test, verify and correct system designs and procedures.

    Assistance to this problem could come in the form of passive treatment technologies. These include Geosynthetic Clay Liners (GCLs) which were shown to attenuate metals from lime treated ARD water. The paper The potential role of geosynthetic clay liners in mine water treatment systems takes a detailed look into this area and conclude that while this technology "may be suitable for short-term containment (< 4 years)in an active–passive treatment system for ARD. They may be suitable for even longer-term use, but more research would be required to verify this hypothesis".

    Impact of Mine Wastes on Geosynthetics

    The mining industry now incorporates geosynthetics in its evaporation ponds, heap leach pads and tailings impoundments as a rule. However, research must be carried out on the effects of various mining leachates on the geosynthetics designed to contain them. The paper The Impact of Mining Solutions/Liquors on Geosynthetics takes a look at a number of mining operations and the leachates generally associated with each of them.

    It rationalises that:

    "Each mining process creates different leachates, each of which could possibly affect the long-term performance of the various polymers which make up the geosynthetic material. The aim of this paper is to define each mining process, the characteristic leachate/liquor associated with the mining process and what effect it might have on the generic polymer of the geosynthetic, as well as on the clay component of the GCLs. It should be noted that while a generic polymer or mineral type may be better suited to than other to a particular application, the chemical constituents may vary within a given polymer or clay type i.e. for example not all HDPE's will perform exactly the same way, which could have a marked effect on relative long-term performance to two HDPE's when compared to each other."

    This paper considers the desirable long-term operating conditions geosythetic materials would have to perform under for a range of mineral mine types. However it also does suggest that:

    "The information provided in this paper is aimed at highlighting potential limitations of a given material and should not be used soley as a design tool as slight changes to leachates can have a significant effect on the perfomance of a geosynthetic material".

    Case Histories

    Composite Liners

    Closure and reclamation activities at the Kennecott Utah Copper Mine include use of liners in the closure of mine waste disposal facilities.

    An interesting case study of mine closure that included the construction of a lined waste disposal facility where mine closure wastes were consolidated is described at this site.

    Floating Covers

    Geotextiles are usually associated with soil reinforcement in embankments and dykes, but their use also extends to the floating cover. In Suncor Energy's Pond 5 reclamation project, a floating cover of petroleum coke was placed on a very soft tailings. This was achieved through the winter placement a geogrid and a geomembrane on the frozen tailings. The geosynthetics then held the coke implace after the spring thaw. For a better overview of the project please see this publication located in the InfoMine Library.


    Other Publications Worth Accessing

    Geosynthetics Research and applications in the mining and mineral processing environment by K. Renken, D.M. Mchaina, and E.K. Yanful.


    Geosynthetics for Uranium Wastes

    Are geosynthetics affected by the constituents you would expect to find in waste disposal facilities at uranium mines? Here are some historical opinions we found on this issue.

    In the Proceedings of the [first] Symposium on Uranium Mill Tailings Management (1978) W. B. Kays writes in his paper Lining Systems for Seepage Control in Uranium Mill Tailings Holding Ponds:

    "Lining choice where radiation is present depends on the total integrated dosage of radiation. The inorganic linings (concrete, gunite, soils, etc.) are not affected much even at high radiation levels. Most organic materials, except fluorine-bearing compounds, degrade rapidly at high doses but speed of degradation is proportional to total integrated dosage. The organic linings generally will adsorb up to a total of around 1010 ergs pre gram of lining material before they are destroyed. This value is often given as 108 rads, since 1 rad is equal to 102 ergs. Uranium ore mine tailings are releasing relatively low amounts of radiation. Each tailings pond would of course vary but a good rule-of-thumb value to use is that the lining in such a pond would be adsorbing some 100 ergs of energy per gram of lining material per hour. Dividing the adsorbing rate in to the material's propensity to adsorb would indicate the lining's life of 108 hours. Since 108 hours is over 11,000 years, radioactive tailings would pose no threat to organic lining life spans due to radiation effects along. The same conclusion can be made with respects to inorganic lining systems."

    Also in 1978, the Nuclear Energy Agency ran a Seminar on Management, Stabilization and Environmental Impact of Uranium Mill Tailings in Albuquerque, New Mexico. R. E. Williams in a paper Control and Prevention of Seepage from Uranium Mill Waste Disposal Facilities, devotes six pages to a detailed survey of geosynthetics in uranium mill waste disposal facilities. He makes no mention of the effects of radioactivity. He simply concludes: "In the case of uranium mill wastes the low pH of the waste water is the most critical factor with respect to liner selection."

    In the following year, 1979, at the Second Symposium on Uranium Mill Tailings Management two papers report on the incorporation of geosynthetic liners into new uranium mill tailings impoundments. Lubina et al report that a "sheet of Hypalon 36 to 60 mil thick" was used to line the Cotter, Colorado uranium mill tailings impoundment. Welsh and Marshall report on incorporation of "1.4 million square feet of 30 mil PVC " at the Sweetwater, Wyoming tailings impoundment. Both papers describe extensive testing of the strength and other physical properties of the geosynthetics. Neither paper mentions testing of the effect of radioactive constituents on the geosynthetics.

    In the proceedings of the third symposium, 1980, is a paper by D.M. Small of Universal Linings, Inc. His nearly forty page paper discusses many aspect of the testing, selection, use, and performance of a variety of synthetic liners at uranium mills and impoundments. There is no mention of response to radioactive constituents.

    The forth symposium in 1981,includes two papers that describe the use of geosynthetics at uranium mill tailings impoundments as follows: Hypalon and hydro-carbon resistant PVC at Elliot Lake in Canada; and 30 mil HDPE alloy liner at Dawn Mining, Washington. Neither mentions radioactivity as an issue in the selection and use of these materials. Also in the proceedings of the forth symposium is a paper by, Buelt and Barnes A Comparative Evaluation of Liner Materials for Inactive Uranium Mill Tailings Piles. They describe extensive testing of the physical and chemical properties and response to uranium mill tailings constituent of soils, asphalt, and geosynthetic liners. There is no mention of the effects of radioactivity etc. on the 1,000-year design life of liners. It would appear that by 1981, the issue was settled: liner materials in uranium mill tailings facilities are not susceptible to the radioactive constituents in the tailings.

    In 1987 the report Canadian Uranium Mill Waste Disposal Technology was published by the Canadian National uranium Tailings Program. The only significant sentence dealing with geosynthetics in the 303-page document is this: "Most commonly used synthetic membrane materials are not likely to be affected by tailings solutions." Both this report and G. M. Ritcey in Tailings Management (1989) quote a 1984 study by Golder Associates (that we were not able to access) who tested nine "polymeric" liners and found "with the exception of polyurethane, the base polymeric resins and asphalt indicated long-term resistance to the constituents in the uranium tailings."

    Ritcey also notes "Synthetic membranes, such as hypalon have been used extensively in uranium tailings, but because of the extremely thin material (20 to 60 mil) they are subject to rupture and therefore the integrity over time is questionable." He provides no information about the chemical stability of the materials used "extensively."

    On the Uranium Mill Tailings Remedial Action (UMTRA) Project, we did not use liners or geosynthetics. Except that at the Durango relocated pile, we placed a GCL in the top deck cover to increase the infiltration impedance of the clays used to limit infiltration and radon emanation. Informal testing by one of my colleagues on the project showed significant radon attenuation by the GCL. The Nuclear Regulatory Agency would not allow us to include the demonstrated effectiveness of the GCL in limiting both infiltration and radon flux into our calculations, although they concurred that inclusion of the GCL was a reasonable thing to do. To my knowledge there are no data on the performance or condition of the GCL to date.

    Thus today we can read and concur that radioactivity is "not a factor unless polymer is exposed to radioactive materials of sufficiently high intensity to cause chain scission, e.g., high level radioactive waste material." Koerner et al. GRI White Paper #6, 2005.

    This paper is a good instance of the design a relatively new uranium milling facility. It includes a detailed design of the liner system, as set out in the application for a Mill Licence.

    Suppliers & Manufacturers

    After becoming familiar with the different types of geosynthetics and their uses, we now can answer the question: Where can one find the right synthetic material for a given problem? Luckily Infomine has all the principal suppliers listed on its site. Some of the most popular are:

    • TenCate have a very long history in the industry, and their site covers almost every type of geosynthetic material that can be purchased today. All of their geosynthetics brochures can he found here.
    • Similarly the Layfield Group manufacture and sell many varients of geotextiles, geomembranes and geogrids to the construction and mining industry.
    • FLI Environmental provide environmental containment solutions for the mining industry, landfill and contaminated land remediation.
    • Bentofix are a company that deal primarily with GCLs and other bentonite related products
    • Cetco also deal with GCLs, in addition to drainage geocomposites and geotextiles
    • XR-5 specialise in geomembranes for pond liners, floating covers and secondary containment
    • Secugrid, as their name suggests specialise in geogrids with "high strength properties"

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