Gretchen L. Bohnhoff

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

AbstractBentonite 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 CaCl2, however, swell of BPC was similar to swell of calcium bentonite ( 2 years). In contrast, Na-bentonite and superabsorbent polymer (similar...

Hydraulic Conductivity of Polymerized Bentonite-Amended Backfills

AbstractThe potential for chemical incompatibility between soil-bentonite (SB) backfills of vertical cutoff walls composed of conventional (chemically unmodified) sodium bentonite (CSB) and contaminated groundwater has led to evaluation of chemically modified bentonites for improved chemical resistance. Accordingly, the hydraulic conductivity to tap water (kw) and to CaCl2 solutions (kc) of SB backfills amended with a polymerized bentonite known as bentonite polymer nanocomposite (BPN) were measured and compared with those for a traditional backfill composed of CSB. The BPN was used both as a dry amendment and as the constituent in the bentonite slurry. Three backfills were evaluated, viz, clean silica sand amended with either 2 or 5% dry BPN and mixed with 2% BPN slurry (i.e., 2BPN2 and 5BPN2, respectively), and the same sand amended with 5% dry CSB and mixed with 5% CSB slurry (5CSB5). Based on permeation with 50 mM CaCl2, the ratio kc/kw varied in the order of 2BPN2<5CSB5<5BPN2, such that the 5BPN2 bac...

SALT DIFFUSION THROUGH A BENTONITE-POLYMER COMPOSITE

Bentonites are commonly used as chemical containment barriers to minimize liquid flow and contaminant transport. However, chemicals can adversely affect bentonite performance to the extent that modified bentonites have been developed to improve chemical resistance relative to traditional (unmodified) bentonites. The present study focused on the diffusion of potassium chloride (KCl) through a bentonite-polymer composite, or BPC, that was known to behave as a semipermeable membrane. Specifically, the effective diffusion coefficients, D*, for chloride (Cl−) and potassium (K+) were measured and correlated with previously measured membrane efficiency coefficients, ω, for the BPC. The values of D* at steady-state for chloride (

Consolidation Behavior of Polymerized Bentonite-Amended Backfills

D_{\rm{ss},Cl^-}^*

Salt Diffusion Through Sodium Bentonite and Bentonite Polymer Composite

Dss,Cl−*) and potassium (

Comparison of Field Data and Water-Balance Predictions for a Capillary Barrier Cover

D_{\rm{ss},K^+}^*