Swelling behavior and microscopic characteristics of a hydrophilic seal in composite geomembrane cutoff walls exposed to various metal-rich solutions

Abstract

This study aimed to investigate swelling behavior, organic composition elution, and microscopic characteristics of a hydrophilic seal exposed to various metal-rich solutions. Results indicated swelling ratios of hydrophilic seal in the monovalent cation (sodium) solutions increased over time until reaching equilibrium; whereas it initially peaked, then gradually decreased and finally stabilized in the multivalent cation solutions. The cation valence was identified as the most significant factor influencing the swelling ratio of weight at equilibrium (S_we), as compared to the other influencing factors (e.g., cation and anion concentrations). The S_we in the 100 mM sodium salt solutions ranged from 328 % to 428 %, which was approximately 10–40 times higher than that in the 100 mM multivalent cation solutions (11–38 %). Based on the microscopic test results, the interaction mechanisms between the seal and metals were interpreted as follows: (1) cations in the testing liquids migrated into the hydrophobic matrix, which in turn reduced osmotic pressure and swelling ability of the seal; and (2) multivalent cations in the testing liquids exchanged with ionized sodium released from the sodium polyacrylate hydrogels, which resulted in chain aggregation or collapse. Therefore, the hydrophilic seal exhibited different swelling behavior in the multivalent cation solution from that in the monovalent cation solution.