A 14-year study on the degradation of LLDPE geomembranes in a highly alkaline heap leaching environment

The longevity of three linear low-density polyethylene (LLDPE) geomembranes (GMBs) with thicknesses of 1.0, 1.5, and 2.0 mm exposed to a pH 13.5 pregnant liquor solution representative of some of the highly alkaline gold and silver heap-leaching solutions was investigated for over 14 years. The GMBs were manufactured from nominally the same resin; however, the 1.5 mm GMB was produced from a different resin lot and with a different antioxidant formulation. Changes in key index properties of samples immersed at 85, 75, and 65 °C were monitored, including oxidative induction time, high-load melt index, tensile break properties, and stress-crack resistance. Based on the observed laboratory degradation rates, Arrhenius modelling was used to project the time to nominal failure ( t NF ) for all three GMBs. The results show that the 1.5 mm-thick GMB exhibited the best overall performance, with t NF projections increasing from the 1.0 mm to the 2.0 mm and to the 1.5 mm GMB. Immersed in the same pH 13.5 solution, the 1.5 mm LLDPE had a longer t NF than a high-density polyethylene (HDPE) GMB of the same thickness. The practical implications of these findings are discussed.