Degradation of polyethylene geomembranes exposed to different mine tailings pore waters

Abstract

The chemical durability of three 1.5 mm geomembranes (GMBs) – two made from high-density polyethylene (HDPE) and one from a blended polyolefin resin – was examined over 3 years in synthetic tailings pore water solutions. The immersion solutions included a pH 4.0 solution simulating pore water from oxidized copper-zinc mine tailings (PW-4), pH 7.0 (PW-7) and 8.0 (PW-8) solutions simulating arsenic-bearing pore waters from saturated gold mine tailings, and a pH 9.5 solution (PW-9.5) simulating pore water affected by cyanide complexes and/or chemicals from a cyanidation plant. Both HDPE GMBs reached nominal failure in stress-crack resistance at 85 °C, followed by reductions in melt index and, in some cases, tensile strength. The blended GMB showed no degradation. PW-7 was the most aggressive solution in terms of degradation of mechanical properties of the HDPEs, while PW-9.5 was the most aggressive for antioxidant depletion for all three GMBs. The relative performance of the three GMBs in different tailings pore waters could not be predicted from the GMBs’ initial properties or the solutions' chemistry. Overall, results highlight the importance of conducting immersion tests for applications involving complex chemical environments.