Comparison of the Durability of Geotextiles in an Alkaline Mine Tailings Environment

This is the last of a three-part study (Grubb et al. 1999, 2000) that explores the issues related to the use and durability of geotextiles in Andean mining environments. Additional outdoor exposure tests were completed on a woven multi-filament polyester (PET) geotextile, and on two nonwoven needle-punched polypropylene (PP) geotextiles with carbon black in Vijus, Peru, and Atlanta, Georgia, USA. The average retained strengths of each geotextile in both locations did not exceed 60%. Five geotextile samples (those previously mentioned and two additional nonwoven needle-punched PET geotextiles) were also embedded in freshly deposited alkaline tailings with a pH of 11.3 and 178 mg/L total cyanide. The retained strengths of the lighter PET geotextile varied from approximately 43 to 338%. The average retained strengths of the four nonwoven geotextiles ranged from approximately 84 to 92%. Two geotextiles placed directly on the surface of the tailings demonstrated that chemical-induced erosion processes could be mitigated. Batch immersion experiments were performed on the PET geotextiles in two alkaline sodium hydroxide solutions (one containing cyanide) to quantify whether the cyanide ion produced any degradation in addition to that measured for the hydroxyl ion at the same pH. The retained strength data indicated that the alkaline solution containing cyanide best matched the alkaline mine tailings environment.