Preparation and properties of cross-linked polymer/bentonite nanocomposite for containment of chemically aggressive liquids

Abstract

Polymer-modified bentonite (PMB) is much more effective at containing chemically aggressive liquids than conventional bentonite. The PMB manufacturing process typically utilizes natural, high-quality sodium bentonite (NaB) owing to its excellent hydrophilicity and swelling capacity. However, calcium bentonite (CaB), which is much more abundant worldwide, is rarely used for containment applications owing to its poor hydrophilicity. This study proposed a polymerization method that transforms sodium-activated calcium bentonite (NCB) into PMB to achieve low hydraulic conductivity ( k ) to aggressive liquids. The mechanism for its low k was revealed through characterization techniques and analyses (e.g. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET)). The results showed that the PMB had a small amount of polymer elution (indicating better interface stability) and thus exhibited excellent barrier properties under chemically aggressive conditions, with the k of < 10 -11 m/s for 0.6 mol/L NaCl solution, which is four orders of magnitude lower than that of the NCB ( k = 3×10 -7 m/s). Various microscopic analyses indicated that the selected monomers were successfully polymerized, and intercalated into and grafted onto the montmorillonite layers of bentonite. The formed polymer network increased the swelling capability of PMB granules, decreased the pore size, and created narrow and tortuous flow pathways leading to a very low k to aggressive liquids.