Cross-Linked Biopolymer-Treated Clayey Soil as a Potential Clay Liner: Consolidation and Sorption Studies with Cadmium and Chromium

The current study introduces a novel cross-linked biopolymer (BP) blend of chitosan and sodium alginate at concentrations of 1%, 2%, and 4% for immobilizing Cr 6+ and Cd 2+ (at concentrations of 300 and 500 mg/kg) in clayey soil. This research aims to develop a biopolymer blended clay liner for landfills and contaminated sites by enhancing sorption while preserving geotechnical integrity. The objective includes evaluating BP's efficacy in heavy-metal immobilization and enhanced geotechnical performance through pH, electrical conductivity, 1-D consolidation, and sorption tests on control (metal-spiked) and BP-treated soils prepared at 70% maximum water-holding capacity. Results show a reduction in void ratio and compressibility, predominantly in the 500-mg/kg Cr 6+ -spiked soil, primarily due to the adsorption and surface complexation of the predominant aqueous hydrogen chromate ( HCrO 4 4 − ) species under acidic conditions, resulting in enhanced particle aggregation and pore volume reduction. Up to 2% BP, all samples meet the linear hydraulic conductivity criteria (≤10 −7 cm/s) and exhibit an increase in sorption capacity. However, 4% BP slightly increases compressibility and conductivity and reduces sorption due to uneven mixing and metal-induced flow paths. Fourier transform infrared spectroscopy confirmed coordination bonds via adsorption and metal chelation in the BP matrix. Optimally, 1% and 2% BP balances superior sorption with geotechnical stability, offering an eco-friendly innovation over conventional stabilizers for heavy-metal containment in clayey soil.