A high-performance polymer-modified bentonite liner for sustainable landfills: from systematic optimization to field...

The containment of aggressive leachates from industrial wastes such as phosphogypsum is a critical geoenvironmental challenge. This study presents a novel bentonite-polymer composite for anti-seepage applications, fabricated by in-situ polymerization of sodium polyacrylate within the bentonite matrix, denoted as PMB-IN. Key synthesis parameters such as temperature, neutralization degree, and the dosages of initiator, crosslinker, and bentonite were systematically optimized. The resulting PMB-IN exhibited an exceptional swelling capacity of 90-100 mL/2 g in deionized water and an enhanced salt resistance of 60-70 mL/2 g in 10 mM CaCl₂. Advanced characterization techniques including FTIR, XRD, and SEM/ESEM revealed a unique phase-separated microstructure. In this structure, a continuous polymer network encapsulates individual bentonite particles, with cationic bridging identified as a key interaction mechanism. This microstructural configuration underpins the significantly improved impermeability and chemical compatibility of the composite. The synthesis process was successfully scaled up using an automated production line, demonstrating a viable route toward industrial application. Furthermore, a sand-bentonite mixture, PMBS, was engineered, incorporating the optimized PMB-IN and evaluated it in a full-scale field test at an actual phosphogypsum impoundment. Under real conditions characterized by strong acidity, high salinity, and multiple heavy metals, the PMBS liner demonstrated superior seepage control and contaminant barrier performance, markedly outperforming a conventional geosynthetic clay liner. This work provides an engineered and high-performance bentonite-based material that effectively bridges molecular-scale design with practical application in sustainable waste containment.