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Abstract

Landfilling is one of the major techniques for the safe disposal of hazardous and municipal waste worldwide. In landfills, a sand-bentonite mixture (SBM) is usually compacted as clay covers and liners. However, due to several unavoidable factors SBM often requires additives for the enhancement. This research focuses on the applicability of two types of polymers to SBM performance enhancement: (1) Polythene terephthalate (PET) based chemically recycled polymer, i.e., Bis (2-hydroxyl) terephthalate (BHET) and (2), Xanthan gum biopolymer. At first, the required BHET polymer content in SBM specimens was evaluated based on four criteria: low hydraulic conductivity, k (<10-7 cm/sec), high unconfined compressive strength, UCS (>200 kPa), higher split tensile strength, STS and low volumetric shrinkage, VS<4%. The polymer addition showed an increment in UCS, STS and a reduction in VS values. Secondly, this research further investigates the effect of the air curing period (1 and 28 days) on the hydromechanical behavior of BHET-treated SBM (0, 1, 2, 3, and 4 % by dry weight). Results from One Dimensional Consolidation tests and hydraulic conductivity of SBM showed a reduction in compressibility due to the pore-clogging mechanism of swollen BHET hydrogel. Thirdly, the study developed and understanding of the effect of the pH on the hydromechanical behavior of BHET-treated SBM (MPs as 0, 1, 2, and 3 % by dry weight). The results of batch adsorption revealed MPs can adsorb Lead ions from the soil as an increase in pH from 4 to 8.5, increasing the removal % for 1000 mg/L ions Pb (II) ions (45.84 to 54.24 %) for 3%. Finally, the fourth study of this research examined Xanthan gum (XG) biopolymer. The performance of XG-treated SBM (0.5, 1.0, 1.5, 2. 0 %) as landfill liner was evaluated by assessing their volumetric, compressibility, and hydraulic properties by conducting one-dimensional swelling, consolidation, and hydraulic conductivity tests, whereas strength characteristics were assessed by estimating unconfined compressive strengths, split tensile strength and effective stress parameters (c' and ϕ') through consolidated drained direct shear tests. SEM and EDX tests support the proposed binding mechanism and conceptual model for the XG-treated SBM.