Application of geomembranes in tailings
Solution Introduction
In the construction of tailings storage facilities (TSFs), the application of geomembranes is the core technical means to prevent toxic and harmful substances (such as heavy metals, cyanides, and acidic water) from seeping into and contaminating groundwater from tailings slag.
Lining System:
Working Principle: Establishing a fully enclosed "seepage barrier." Tailings slurry contains a large amount of residual chemical beneficiation agents and acidic substances. HDPE geomembranes, with their excellent chemical resistance, can effectively isolate these highly corrosive liquids.
Specification Recommendation: Tailings dams operate under high pressure; HDPE geomembranes with a thickness of 1.5mm or 2.0mm are typically used.
Upstream Face Seepage Prevention of Tailings Dams:
Working Principle: Laying a geomembrane inside the dam body prevents water accumulation within the tailings dam from seeping into the dam structure, causing a rise in the wetting line, thereby avoiding landslides or dam failures and ensuring the physical stability of the dam structure.
Capping
Working Principle: After the tailings dam is closed, a geomembrane is laid on top.
Purpose: To prevent rainwater infiltration and the generation of new leachate, while also preventing harmful dust in the tailings from being blown away by the wind and blocking the escape of acidic gases.
Construction Specifications
I. Subgrade and Protection Specifications
Tailures typically contain sharp slag; subgrade treatment is the first line of defense against damage.
Smoothness Requirements: The subgrade should be compacted and leveled, removing all stones, tree roots, or sharp debris larger than 5mm in diameter.
Protective Layer Configuration:
Specification Requirements: A protective layer (usually 600g/m² or higher filament geotextile or GCL) must be laid under the geomembrane.
Geoleed Experience: If tailings pressure is extremely high, it is recommended to also cover the membrane with a layer of nonwoven geotextile to prevent damage to the membrane during tailings filling.
II. Installation and Seaming Specifications
Slack:
Core Specification: Tailings dams experience significant settlement; a 2%–5% allowance must be allowed during installation.
Special Requirements for the Middle East: When constructing in Saudi Arabia, diurnal temperature variations must be considered. It is strictly forbidden to stretch and lay the geomembrane during the midday heat, otherwise the drop in temperature at night will cause the weld to crack due to excessive shrinkage stress.
Welding Technology:
Main Weld: A double-rail hot-melt welding machine must be used. The effective width of the weld should not be less than 10mm.
Special Locations: At dam slope intersections, pipe roots, and other locations, single-rail extrusion welding should be used.
Joint Layout: Longitudinal joints on the slope should be arranged along the slope, and the joint position should be at least 1.5 meters away from the toe of the slope.
III. Anchoring and Counterweight Specifications
Anchoring Trench: Due to the long tailings dam slope, the anchoring trench depth usually needs to reach 80cm-100cm.
Timely Backfilling: The geomembrane in the anchoring trench should be backfilled and compacted with clay as soon as possible to prevent strong winds from lifting or tearing the membrane surface.
Temporary Counterweight: During construction, sandbags should be placed on the membrane surface every 2-5 meters to prevent displacement.
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Working Principle
1. Hydraulic Pressure Barrier Principle: This is the most fundamental physical working principle of tailings seepage control.
Extremely Low Permeability: Tailings slurry contains a large amount of water and chemical agents. High-density polyethylene (HDPE) geomembrane, as a non-polar material, has a permeability coefficient of ∝ K ≤ 1.0 × 10⁻¹³ cm/s.
Blocking Principle: Under tall tailings dams, the bottom is subjected to enormous hydrostatic pressure. The geomembrane, through its dense molecular structure, establishes a near-absolute physical barrier between the tailings slurry and groundwater, making the seepage flow approach zero.
Combined Effect: When a geosynthetic clay mat (GCL) is placed under the membrane, even if the membrane is accidentally punctured, the extremely low permeability layer formed by the expansion of the GCL upon contact with water will adhere tightly to the membrane, utilizing the principle of "contact resistance" to eliminate lateral flow and control leakage within a limited range.
2. Chemical Inertness and Anti-Degradation Principle: Tailings environments are typically highly acidic (e.g., gold and copper mines) or alkaline (e.g., alumina red mud dumps), and contain corrosive agents such as cyanides.
Molecular Stability: The long hydrocarbon chain structure of HDPE geomembranes is very stable and does not undergo displacement reactions with strong acids or bases.
Oxidation-Induced Inaction (OIT): During operation, metal ions in tailings catalyze the degradation of polymers. The antioxidants added to Geoleed products neutralize free radicals by sacrificing themselves, thereby protecting the polymer chains and maintaining their mechanical strength over a service life of 50-100 years.
3. Three-Dimensional Strain Compensation Principle: A significant characteristic of tailings dams is their massive load and uneven settlement.
Flexible Deformation Mechanism: When the foundation at the bottom of the reservoir experiences localized settlement due to tailings accumulation, the geomembrane, with its excellent yield elongation and environmental stress cracking resistance (ESCR), can stretch and deform like "skin" without breaking.
Lateral Restraint Principle (for slopes): On slopes, the textured geomembrane, through its surface friction protrusions, creates an "interlocking effect" with the soil, transferring the sliding force of the tailings to the anchoring trench, preventing the seepage prevention system from sliding under immense accumulation pressure.
Address
Production Center: Development Zone, Tai'an City, Shandong, China
Marketing Center: Ichi-no-Machihigashi, Sakai-ku, Sakai City, Osaka, Japan