Long-Term Hydraulic Conductivity of a Bentonite-Polymer Composite Permeated with Aggressive Inorganic Solutions: Fid-Bau Portal

Long-Term Hydraulic Conductivity of a Bentonite-Polymer Composite Permeated with Aggressive Inorganic Solutions

Scalia, Joseph / Benson, Craig H. / Bohnhoff, Gretchen L. / Edil, Tuncer B. / Shackelford, Charles D.

Abstract

Bentonite was modified to prevent alterations in hydraulic conductivity when permeated with aggressive inorganic solutions. Acrylic acid within bentonite slurry was polymerized to create a bentonite-polymer composite (BPC). Tests indicate that BPC generally swells more and retains low hydraulic conductivity compared with natural sodium bentonite (Na-bentonite) when contacted with aggressive inorganic solutions. BPC in deionized water swelled greater than 3.8 times the swell of the Na-bentonite used to create BPC (73 versus $19 mL / 2 g$ ). In 500 mM ${CaCl}_{2}$ , however, swell of BPC was similar to swell of calcium bentonite ( $< 10 mL / 2 g$ ). Thin layers of BPC simulating geosynthetic clay liners were permeated directly with 5–500 mM calcium chloride ( ${CaCl}_{2}$ ) solutions and extreme pH solutions (1 M NaOH with pH 13.1, 1 M $HN O_{3}$ with pH 0.3). BPC maintained low hydraulic conductivity ( $< 8 \times 10^{- 11} m/s$ ) for all solutions for the duration of testing ( $> 2 years$ ). In contrast, Na-bentonite and superabsorbent polymer (similar to the polymer in BPC) permeated with the same solutions had hydraulic conductivities at least three orders of magnitude higher (except for 5 mM ${CaCl}_{2}$ ). Hydraulic conductivity of BPC does not follow the classical hydraulic conductivity-swell relationship typical of Na-bentonite. BPC eluted polymer during permeation but maintained low hydraulic conductivity. Polymer elution was lower in more concentrated ${CaCl}_{2}$ solutions.