Long-Term Performance of Geosynthetic Clay Liners Used in Acid Rock Drainage Mitigation

Abstract

Longterm barrier performance of geosynthetic clay liners (GCLs) when exposed to acid rock drainage (ARD), which is one of the most severe and expensive environmental problems facing the mining and some construction operations, was evaluated. Free swelling, sorption, and a ninemonth hydraulic conductivity tests on a needle punched GCL against an artificial ARD (pH = 3) that contained Al, Fe, Cu, Zn, As, and Pb, were conducted. Free swelling tests showed that a high metal concentration and/or a low pH negatively impacted on osmotic swelling. Sorption test results provided information about the competition among metals, and the Nabentonite capacity to sorb single metals and metalloids. Ninemonth hydraulic conductivity tests demonstrated that pH, EC and permeability changes over time, due to metal sorption/release and precipitation (physical clogging). The hydraulic conductivity remained low during the test duration and was approximately five times lower when GCL was prehydrated with water before ARD permeation (1.1x10 10 m/s) compared to the case in which prehydration and permeation were done using ARD (5.0x10 10 m/s). In each case, effluents were evaluated and breakthrough curves were constructed to get information about the GCL attenuation capacity toward metals present in ARD. Considering that bentonite (or GCLs) has the potential to retain heavy metals present in solution, showed relatively low hydraulic conductivity under even extreme conditions, and is available in many parts of the world, GCLs seem to be one possible solution for ARD mitigation.

Factors influencing hydraulic conductivity and metal retention capacity of geosynthetic clay liners exposed to acid rock drainage

“…However, the hydraulic conductivity of GCLs may change over time especially due to metal interaction or precipitation. Naka et al (2011) found that hydraulic conductivity of GCL permeated with ARD gradually increased over time, until around 150 PVF. After this point, it stabilized, reaching an average permeability value of 5.0×10 -10 m/s.…”