The need to protect groundwater resources from the contaminating effects of toxic liquids has created a thriving market for the manufacturers of synthetic, “impermeable” geomembranes. Miners seeking to construct low-permeability pads to retain cyanide solutions in heap leaching operations, pregnant solution ponds, tailings dams, etc. can now consult a number of suppliers. We’ve compiled some of the pertinent specifications from five manufacturers supplying the North American market.
Nilex
Nilex Geotechnical Services provides contractors with flexible membrane panels up to 4,000 square metres in size — depending only on site-handling capabilities and weight restrictions.
The company provides engineers and contractors with appropriate panel layout and design, including details relating to anchor trenching, mechanical fastening and treatment of any necessary openings in the geomembrane. It also researches and evaluates all technical reports and papers published on relevant subjects and indexes these for customer use.
At Nilex’s fabrication plant, in Edmonton, Alta., ultra-wide panels are turned out quickly. In-house production reduces the on-site seaming that is often undertaken under difficult conditions, and this of course can result in cost-savings for customers.
In Canada, Nilex has installed liners for two heap leach pads — one at the Hope Brook gold mine in southwestern Newfoundland, in 1987, and another for Candorado Mining in Hedley, B.C. this spring. The former was a double-lined pad utilizing a 30-mil pvc secondary liner and a 60-mil high-density polyethylene (HDPE) primary liner.
At the remote Hope Brook minesite, an 85,000-square-metre heap leach pad was required. Nilex participated in the evaluation of the liner material, the base preparation and the ore load design. The 80-mil HDPE liner was installed in record time and has functioned as per design, according to company literature. High winds, coastal fog and the remote location all provided additional challenges to the Nilex installation crew.
The company employs Novex smooth surface sheet, which is produced from Novacor polyethylene resin specifically designed to give superior properties in geomembrane sheet applications. Because it optimizes resin characteristics, the sheet features an outstanding combination of strength and toughness as well as exceptional flexibility. It is available in standard rolls up to 5,000 kg in various thickness types.
Nilex has branches in Calgary, Alta., Vancouver, B.C., Denver, Colo., and Ventura, Calif.
SLT North America
SLT North America of Houston, Tex., manufactures and installs durable HDPE geomembrane lining systems for virtually any containment problem facing the mining industry.
SLT Ultraflex T-101 is a membrane liner with high uniaxial and multiaxial elongation characteristics, which make it highly suitable for applications (such as heap leaching) where differential or localized subgrade settlements are expected. Ultraflex contains 97.5% polymer and 2.5% carbon black, anti-oxidants and heat stabilizers.
Ultraflex is manufactured 9.85 metres wide and up to 270 metres long and, according to company literature, is the world’s largest monolithic geomembrane lining material.
Also used for leach pad applications is SLT’s Hyperflex. Its mechanical resiliency and chemical inertness are available in the largest monolithic sheets and the greatest thickness range offered in the industry, according to SLT. The company insists that Hyperflex carries several distinct advantages over other HDPE liners:
* Environmental stress check resistance is said to be as much as three times superior to other HDPE liners.
* Dimensional stability is said to be superior to other liners, especially in high-temperature exposure.
* Superior resistance to cold climates reduces embrittlement and failure due to cold environments.
* Considerable field seam strength enhances containment integrity.
* Considerable impact strength and toughness provide integrity under full load.
Because of its resistance to abrasion, Hyperflex is often chosen to line thickener tanks or other types of operating units employing scraper arms. Concrete settlement tanks, vats, sumps or other structures forming solvent extraction systems may be protected from corrosion with Hyperflex.
For tailings applications, SLT recommends its FrictionFlex textured liner. Its high-friction surface provides stability for steeper slopes, thus increasing volume and efficiency, the company says. Vertical expansions and perimeter slopes in closures share the benefits of greater airspace and superior cover stability.
This textured liner (textured, that is, on one or both sides) exhibits the same mechanical and chemical properties demanded of SLT’s Hyperflex HDPE geomembrane. Non-textured edges facilitate welding and thickness measurements for superior quality control. Standard installation equipment and procedures ensure expedient construction.
Rematech Industries
Rematech Industries of Oakville, Ont. fabricates and installs Hypalon pond liners to contain fluids for mining companies in Ontario, Quebec and elsewhere. The membrane is fabricated in advance into sheets up to 1,800 square metres, which are later joined in the field.
Hypalon is well-known for its ozone resistance and colorability (it can be compounded in white or in a wide range of colors that can remain stable under sunlight exposure). It is widely used in industrial maintenance because of its proven performance in hose, belts, rolls, gaskets, diaphragms, protective gloves, garments, linings and coatings. Other applications include electrical uses, automotive uses and construction products.
Hypalon liners are unique in that they are produced and shipped in the uncured state. Field seaming uses solution adhesives and is quick and sure. After installation, Hypalon gradually achieves a state of cure which produces an even stronger, tougher and weatherable rubber liner.
Poly-Flex
The Poly-Flex division of Poly-America manufactures Dura-Flex VLDPE-A liners (the acronym stands for very low density polyethylene-alloy). The VLDP resin has a specific gravity of 0.900 to 0.912 and a melt index of less than 0.6 g/10 min. Carbon black is added to the resin of the geomembrane for ultra-violet resistance. Thicknesses are 20-mil, 30-mil, 40-mil and 60-mil.
First Mississippi Gold installed a 30-mil Dura-Flex VLDPE-A liner from Poly-Flex as a liner for a heap leach and residual sodium cyanide impoundment at its Getchell mining operation in Golconda, Nev. The design engineering firm of Steffen Robertson & Kirsten chose Dura-Flex for structural and economic reasons.
The project required a total of 697,000 square metres of Dura-Flex liner. One 40-ha area with an embankment height of 21 metres and a second area, 71 ha in size with 32-metre embankments was covered. The project was completed on time at considerable savings over the cost of the 60-mil HDPE previously used.
Gundle Lining Systems
Houston, Tex.-based Gundle, the largest manufacturer of HDPE liners in the world, now produces material that is more than 10.3 metres wide in various thicknesses. The new width of liner is available as Gundline hd (high-density polyethylene) and Hyperlastic (very low density polyethylene). The 103-metre-wide liner allows for faster installation by the reduction of field seams.
Also, Gundle now offers a prefabrication service. The company can now fabricate HDPE or VLDPE into custom-sized sheets. And sumps, penetrations and tanks can be prefabricated for improved installation efficiencies.
Other manufacturers of geomembrane liners include Fluid Systems of Cincinnati, Ohio, Amoco Fabrics & Fibers Co. of Atlanta, Ga., and Watersaver Co. of Denver, Colo.
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