Golden Hills Heap Leach Project

Leister equipment is “good as gold” in Mongolia installation

In October 2013, two companies based in Ulaanbaatar, Mongolia, Bayan Airag Exploration LLC (a mineral exploration and development company), and Usny Erchim Co., Ltd (Leister Technologies’ official sales partner), found themselves at the Northwestern region of Mongolia collaborating on the Golden Hills Heap Leach Project.

Heap leaching is an industrial mining technique used when extracting precious metals―like copper, uranium, gold, and other compounds—from ore via a series of chemical reactions.

The ore is first crushed and then “heaped” into large piles on plastic sheets which protect the soil against contamination. Once the solvent (typically cyanide) seeps through the piles of material, and bonds with the metal contained therein, the solution is then collected at the bottom of leach tanks as an enriched solution and pumped to a mill where more chemicals are used to separate the cyanide from the valuable metals. Therefore, it is of extreme importance that those plastic layers are absolutely leak-proof.

Leister, the right partner 
The overall scope of the Golden Hills project was to provide quality installation of a double geomembrane liner system, which included GCL Heap leach pads, collection ditches, and emergency ponds and storm ponds during diverse weather conditions.

More than 60 pieces of haul trucks and heavy equipment handled all of the earthworks at the open pit mine, which hauled the ore to the heap leach pad complex. In total, the Golden Hills Project employed approximately 500 people.

The installation of the geosynthetics liner was deftly managed by a crew of 25. The crew was comprised of one foreman, two quality controllers and six welding technicians, from Usny Erchim Co., Ltd. as well as another 16, locally-hired assistant workers. To date, the geo installation crew has welded an estimated 315,000 sq. meters (3.4M sq. ft.) of geosynthetic liner.

For this particular project, Usny Erchim not only served as Leister’s distributor and partner, but also as the geo installation crew. As a Leister partner, the team from Usny Erchim already had the requisite tools and spare parts necessary for such a project. The team gained great experience as they witnessed first-hand, how well the Leister tools performed in such a harsh climate.

During the first stage, the team installed four lined leach pad cells, a 450 m (1,476 ft.) collection ditch, emergency ponds, and storm ponds. Throughout the second stage, the team added six (similarly-sized) leach pad cells and an additional collection ditch.

The liner system of the Heap Leach pad consisted of an underlying layer of geosynthetic clay liner or GCL (GCL is a clay lining material, largely used to line landfills), primary and secondary geomembrane liners, and a final layer of geonet―a synthetic drainage material manufactured from the highest quality, high-density polyethylene (HDPE) resin.

Leister, reliable tools in harsh environments
The climate at the site can be described as oppressive, with summer temperatures reaching up to 40 C (104 F), or it can be described as downright frigid during the winter months with temperatures plummeting to -40 C (-40 F), and with very little precipitation year around. 

In this arid, semidesert area, where dust storms occur regularly during summer and snow storms occur during winter, Leister’s line of high-quality and robust tools were perfectly-suited for the job.

When faced with the cold temperatures, the team’s main solution for quality welding was the preheating of the material and equipment. All fused seams—up to 140 m (460 ft.) in length―were welded predominantly by the COMET automatic welder. The COMET, with a set temperature of 420 C (788 F) and pressure of 800N (180 lbf) steadily welded the 1.5 mm HDPE material at 2.0 - 2.7 m (6.5 – 9.0 ft.) per minute, depending on weather conditions.

All patches were completed using the FUSION 3 extrusion welder and TRIAC hot-air tools. The welding temperature of the FUSION 3 was set at 180 – 220 C (356 - 428 F), again weather dependent. Additionally, the team also had at their disposal, an ASTRO wedge welder, FUSION 2 extrusion welder, EXAMO USB tensiometer, and the TRIAC S and TRIAC AT hot-air
tools.

Weld Quality
The installers used 1.5 and 2.0 mm, smooth HDPE geomembrane. The weld quality satisfied the standard MNS GRI-GM19: 2011 approved by the Mongolian Agency of Standardization and Measurement (this standard was adapted from Geosynthetic Institute, Folsom, Pa.).

Performance and reliability
Leister’s equipment designed for use in civil engineering applications did a great job in the fluctuating weather conditions. The COMET and FUSION 3 achieved the same quality welds whether they were used during the autumn, spring, and/or summer months of the Golden Hills project.

Leister was chosen for this project not only because the Swiss company is the leading supplier of plastic welding technologies and has an excellent international reputation, but also because their portfolio of civil engineering equipment—which did a great job at this challenging site. Bayan Airag Exploration and Usny Erchim found the right partner in Leister Technologies.

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Leister Sales and Service Center: Usny Erchim, Ulaanbaatar, Mongolia
Customer: Bayan Airag Exploration LLC, Mongolia
Material: HDPE geomembrane
Leister Products: COMET, FUSION 3, ASTRO, TRIAC, EXAMO USB
Text / Photos: Leister AG and Usny Erchim Co.