Diffusion of metals in geosynthetic clay liners

The potential for using geosynthetic clay liners (GCLs) to mitigate metal mobility is dependent, in part, on consideration of its effectiveness as a diffusive barrier. In this context, laboratory-measured diffusion coefficients and supporting sorption data for metals (Al, As, Cd, Cu, Fe, K, Mg, Mn, Ni, Sr, Zn) are reported for the following four cases where a GCL might serve as an effective barrier material to metals and metalloids: acidic rock drainage, gold mine tailings, lime-treated mine effluent, and municipal solid waste. The average diffusion coefficients for Cu, Cd, Zn, Fe and Ni covered a narrow range from 0.67 × 10 −10 to 0.89 × 10 −10 m 2 /s. The diffusion coefficients for As, Al, Mg, Mn and Sr were in the range D = 0.80 × 10 −10 to D = 1.6 × 10 −10 . The diffusive movement of other more common inorganic ions such as Ca, Na, S (SO 4 ) and Cl are also considered, as well as the impact of pH, Eh and speciation on metal mobility in GCLs.