Blended polyolefin geomembrane degradation in water and extreme pH mining environments

Three blended polyolefin (BPO) geomembranes (GMBs) with nominal thicknesses of 1.0 mm (BzSw10), 1.5 mm (BzSw15), and 2.0 mm (BzS20) were immersed for 9.3 years in highly acidic (L1-pH 0.5) and highly alkaline (L8-pH 13.5) heap leaching solutions, and water (pH 6.5–7.6), at 85, 75, and 65°C. The solutions simulated pregnant liquors from metal recovery processes. BzSw10 and BzSw15 shared the same resin and antioxidant package, while BzS20 had a different formulation. All three comprised around 90% linear low-density polyethylene (LLDPE) and 10% high-density polyethylene (HDPE) resin. Times to antioxidant depletion and nominal tensile failure generally increased from BzSw10 to BzSw15 to BzS20 across all media. Among the solutions, pH 13.5 was the most aggressive, causing faster antioxidant depletion and onset of degradation, followed by water (pH 6.5–7.6) and pH 0.5. In pH 13.5, melt index and break strength initially decreased but later stabilized at low values, reflecting the strong influence of solution chemistry. Compared to a HDPE GMB previously immersed in the same pH 13.5 and pH 0.5 solutions, the BPOs exhibited faster antioxidant depletion but generally outperformed the HDPE in terms of mechanical property degradation, including break strength and stress-crack resistance.