Heavy metal sorption and hydraulic conductivity studies using three types of bentonite admixes

Bentonite, forest soil, and spruce bark were submitted to batch adsorption testing, leaching cell testing, and selective sequential extractions (SSEs) to investigate the heavy-metal compatibility of clay barriers and the potential of forest soil and spruce bark as clay barrier materials. The materials ranked as follows according to sorption capacity: forest soil > bentonite = spruce bark. The hydraulic conductivity values of heavy metal leachates were two orders of magnitude greater than those of the blank (0.01 mol calcium nitrate) leachate. The forest soil admix ranked first in terms of heavy-metal retention capacity and breakthrough points. The mobility of Cd was 4.5 times higher than that of Pb, and Cu was 2.5 times more mobile than Pb. The leaching cell and SSE results indicate that heavy metals cause significant preferential channeling. The SSE results show that the addition of forest soil and spruce bark to clay barrier mixes promotes heavy-metal fixation.