Polymer Fouling and Hydraulic Conductivity of Mixtures of Sodium Bentonite and a Bentonite-Polymer Composite: Fid-Bau Portal

Polymer Fouling and Hydraulic Conductivity of Mixtures of Sodium Bentonite and a Bentonite-Polymer Composite

Scalia IV, Joseph / Benson, Craig H.

The impact of entraining water-soluble polyacrylate eluted from a bentonite-polyacrylate composite (BPC) in sodium bentonite (Na-bentonite) was evaluated as a means to achieve low hydraulic conductivity to aggressive ${CaCl}_{2}$ solutions that reduce interlayer swell in conventional Na-bentonite. Up to 73% of the polymer initially contained within BPC (28.5% polymer by mass) was soluble and elutable polyacrylate. This polymer fouled pores that would typically conduct the bulk of flow in Na-bentonite permeated with aggressive ${CaCl}_{2}$ solutions ( $\geq 50 mM {CaCl}_{2}$ ). Similar fouling was observed with kaolinite and low-plasticity clay combined with BPC, but not fine sand or nonplastic silt combined with BPC. Granular mixtures of Na-bentonite blended with BPC had hydraulic conductivity to 50 mM ${CaCl}_{2}$ as much as 1,500 to 6,700 times lower than Na-bentonite alone. Blends of granular Na-bentonite and granular BPC with as little as 1% BPC had hydraulic conductivities lower than BPC alone when permeated with 50 mM ${CaCl}_{2}$ . However, mixtures of BPC and Na-bentonite did not exhibit low hydraulic conductivity to 500 mM ${CaCl}_{2}$ unless the mixture contained at least 90% BPC. The findings suggest Na-bentonite-BPC mixtures have the potential to be tailored to contain specific leachate chemistries. Mixtures of BPC with other clay soils (viz kaolinite, low-plasticity clay) may also be effective in achieving very low hydraulic conductivity with aggressive solutions.