Antioxidant depletion in high-density polyethylene (HDPE) geomembrane with hindered amine light stabilizers (HALS) in low-pH heap leach environment

Abstract

Antioxidant depletion from a high-density polyethylene (HDPE) geomembrane with hindered amine light stabilizers (HALS) immersed in seven different low pH solutions is examined over a 3 year period. The examined solutions had the range of pH (0.5, 1.25, and 2.0) likely to encompass the pH of the leach solutions found in copper, nickel, and uranium heap leach pads. The metal concentration for these solutions is adopted from copper raffinate solutions. Additional solutions are investigated to examine the effects of field practices such as using surfactants in the leach solutions and pre-curing of the ores used to improve the metallurgical response of the ore. For the antioxidants detected by standard oxidative induction time (Std-OIT), there was a depletion to residual value of about 20% of the initial Std-OIT that varied depending on the incubation temperature and pH of the solution whereas decreasing the pH from 2 to 0.5 did not significantly affect the depletion rates of Std-OIT. The antioxidants detected by high-pressure oxidative induction time (HP-OIT) exhibited the fastest depletion in pH = 1.25 with the highest residual values followed by pH 2.0 and the slowest HP-OIT depletion was in pH = 0.5, but with the lowest residual values. Arrhenius modelling is used to predict the length of the antioxidant depletion stage for each solution based on both Std-OIT and HP-OIT.