Metal retention in geosynthetic clay liners following permeation by different mining solutions

The leaching of hazardous metals and metalloids from mine tailings is a significant problem facing the mining industry. Although, in the past, geosynthetic clay liners (GCLs) have primarily been employed as leachate barriers in landfills, recent times have seen an increase in the variety of their applications, including applications in the mining industry. The capacity of GCLs to attenuate metals and metalloids (As, Al, Cd, Cu, Fe, Mn, Ni, Sr, Zn) from mine acidic rock drainage (ARD) water and a neutral-pH, As-rich water associated with gold mine tailings (GMT) was evaluated. Water- prehydrated GCLs were permeated with GMT and ARD for short (2 and 5 pore volumes, PV) and long (21 PV) periods. The long- term hydraulic conductivity of the GCLs increased from 1.6 x 10(-11) m/s (water for 5 PV) to 5.0 x 10(-11) m/s and 1.3 x 10(-10) m/s after permeation with the GMT and ARD waters, respectively (21 PV). The distribution of metals within the GCL was quantified in order to differentiate between metals associated with precipitated compounds, soluble complexes in porewater, and sorbed metals. Metals sorbed to the GCL are reported in micrograms of metal per gram of bentonite (ppm), and are indicative of the GCL's sorption capacity for a barrier system. Significant differences existed between the soil tested at 2 PV, 5 PV and 21 PV. It was only at 5 PV that the precipitation of the ferrihydrite occurred in the ARD samples, and gypsum occurred in the GMT samples. These minerals were responsible for retention of metals in addition to the cation exchange of the GCL.