Why chemistry (not just pH) should drive liner selection

Disclosure. The findings cited below are from Silva, Rowe & Abdelaal (2025). The three 1.5 mm polyethylene geomembranes tested are anonymised by the authors and are not Atarfil products. We’re aligning practice with their results, not claiming their data as ours.

What the study did (in brief)

• Applications simulated. Four synthetic tailings pore waters (“PW”) representing common mine environments:
  PW-4 (pH 4): oxidised Cu–Zn tailings; high Mg/Mn/Zn/SO₄. PW-7 (pH 7): arsenic-bearing saturated gold tailings. PW-8 (≈pH 8): carbonate-buffered variant of PW-7. PW-9.5 (≈pH 9.5): cyanide/caustic-affected pore water.

• Method. Double-sided immersion per ASTM D5322 at 85/75/65/40 °C, with periodic solution refresh, tracking Std-OIT (D3895/D8117), HP-OIT (D5885), SCR (D5397), tensile (D6693), HLMI (D1238) for up to 36 months.

• Baseline. All three materials far exceeded GRI GM13 off-the-roll properties before testing.

What it found (and why it matters on site)

• Neutral pore water can be the most damaging—mechanically. PW-7 (pH 7) drove the fastest HDPE mechanical degradation (SCR/tensile), whereas PW-9.5 drove the fastest antioxidant depletion for all three GMBs. Conclusion: chemistry profile (ions/complexes) beats simple pH as a risk indicator.

• OIT ≠ life. Mechanical degradation (Stage II/III) can begin before OIT is “zero”; antioxidant depletion and mechanical damage are related but distinct.

• Initial index values don’t rank long-term performance. Materials with higher initial SCR or OIT didn’t always last longer under specific chemistries; relative behaviour depended on resin and liquor composition.

• Field relevance. TSF liners commonly contact near-neutral pore waters at depth; alkaline conditions arise with cyanide/caustic circuits; acidic zones can develop nearer the surface or in filtered stacks where oxidation fronts migrate.

Application-by-application risk map (from the paper’s chemistries)

Application context	Representative chemistry	Dominant risk mechanism observed	Design implication
Saturated gold TSF base / decant pond liners	PW-7 (pH 7) with As/Cl⁻	Fastest mechanical degradation (SCR loss) of HDPEs despite neutral pH	Prioritise resin with proven SCR retention and tensile stability in neutral, saline liquors; don’t rely on pH as “benign”.
Cyanide/caustic circuits; alkaline seepage zones	PW-9.5 (~pH 9.5)	Fastest antioxidant depletion (Stage I), mechanical effects later	Specify alkali-resistant antioxidant packages and verify OIT retention under alkaline/brine immersion.
Oxidised zones (Cu–Zn)	PW-4 (pH 4) with metals/sulphate	Moderate antioxidant depletion; mechanical impacts depend on resin	Neutral pH elsewhere can still govern life—test both acidic and neutral site liquors.

Why high-performance HDPE—even at neutral pH

1. Neutral ≠ low-risk. The fastest HDPE mechanical damage occurred in PW-7 (pH 7); choosing GM13/GM17 minimums by pH alone is unsafe.
2. Index minima are not durability metrics. All three materials met GM13, yet diverged in long-term behaviour; selection must consider resin chemistry and immersion performance, not just off-the-roll numbers.
3. Mechanics drive consequence. SCR loss under sustained strain governs crack initiation at stress raisers and defects; that’s what limits service life, not OIT on its own.

How Atarfil addresses these mechanisms (without implying inclusion in the study)

• Alkaline/brine durability (Stage I): ATARFIL EVO AR (Alkaline Resistant) is designed for very high pH; baseline Std-OIT ≥ 150 min, HP-OIT ≥ 2000 min, with ≥ 55 % Std-OIT retention after 200 days in concentrated brine at ~pH 10 (60 °C).

• Stress-crack resistance (Stage II/III): SCR ≥ 3000 h (ASTM D5397/ISO 18488) with structured-textured manufacturing that maintains elongation and consistent asperity—important where liners see ongoing tensile strain (steep slopes, strain from settlement).

• Friction & handling: Structured texture targets asperity ~0.60 mm (min 0.45 mm) and interface friction ≥ 29° with 1000 g/m² PP geotextile, supporting shear design on steep TSF geometries.

Note. The paper’s tested materials are anonymised and are not identified as Atarfil; the data above comes from Atarfil datasheets and is shown only to map how our specifications address the same failure pathways the study measures.

Recommended workflow for designers and owners

1. Characterise site liquors (lab ICP plus anions, alkalinity, COD as needed) and run ASTM D5322 double-sided immersion at 85/75/65/40 °C for ≥ 6–12 months, tracking Std-OIT/HP-OIT, SCR, tensile, HLMI to capture both depletion kinetics and mechanical response.
2. Decide on mechanics, not OIT alone. Use onset of SCR change and time to nominal failure as go/no-go gates; OIT informs Stage I only.
3. Design the system. Neutral or alkaline liquors still need composite liners (GMB + GCL/protection) to manage both chemistry and defect sensitivity over multi-decade horizons.

Conclusion

While all three geomembranes in the study met GM13 HDPE requirements when new, their long-term performance in real tailings liquors diverged dramatically. In particular, the pH 7 arsenic/chloride solution caused the fastest mechanical degradation (stress-crack resistance and tensile loss) in the HDPEs—despite being “neutral” and often considered benign—while the pH 9.5 alkaline liquor drove the fastest antioxidant depletion. These results show that GM13’s minimum index properties are a quality control baseline, not a durability guarantee. For tailings, heap leach, or any application with heavy metals, salts, or other non-inert chemistry, and with design lives beyond 20 years, material selection must be based on site-specific immersion testing and mechanical property retention in the actual process water, not just compliance with a generic index specification.

Reference

e Silva, R.A., Rowe, R.K., Abdelaal, F.B. (2025). Degradation of polyethylene geomembranes exposed to different mine tailings pore waters. Geotextiles and Geomembranes, 53, 1483–1505. (36-month, four-liquor immersion; HDPE×2 & blended; PW-7 fastest for mechanics; PW-9.5 fastest for antioxidant depletion.)