LEAD RETENTION MECHANISMS AND HYDRAULIC CONDUCTIVITY STUDIES OF VARIOUS BENTONITES FOR GEOENVIRONMENT APPLICATIONS

Abstract

Four bentonites from various sources were exposed to batch adsorption testing, selective sequential extraction and consolidation tests to investigate their metal retention capacity and hydraulic conductivity for geoenvironmental application such as in clay barrier materials. The Japanese bentonites (JB1–JB3) contain ∼2–4% of carbonate and trace amount of zeolite (JB2 and JB3), whereas the US bentonite has <1% carbonate and no zeolite. The rank of smectite content in the bentonites are USB > JB1 > JB3 > JB2. The materials ranked as JB2 ≈ JB3 > JB1 > USB, according to retention capacity, while after the removal of carbonate the retention capacity order was JB1 ≈ JB2 ≈ JB3 > USB. SSE results indicate that carbonate plays a major role at low Pb solution concentration and precipitate as PbCO3. Once the carbonate is exhausted, the clay composition dominates the sorption process. The hydraulic conductivity of the bentonite mixtures (basalt+10% bentonite) using water was kUSB < kJB1 < kJB3 < kJB2, consistent with the smectite content and swelling power, with USB having the highest proportion of smectite. Among the Japanese bentonites studied, JB1 is the best candidate for barrier material, comparable to the widely used USB.