From macroscopic performance to molecular mechanisms: Multi-scale insights into enhanced impermeability of EMS/PAAS composites

Leakages of electrolytic manganese slag (EMS) disposal sites pose a significant threat to soil and groundwater, necessitating effective in situ remediation technologies. This study presents a multi-scale analysis to elucidate the enhanced impermeability mechanism of EMS composite modified by sodium polyacrylate (PAAS). By integrating macroscopic performance testing (compressive strength, permeability, corrosion resistance, and pollutant leaching), molecular dynamics (MD) simulations, and advanced spectroscopic/microscopic techniques (FTIR, XPS, and EDS mapping), we establish a direct link between macroscopic properties and underlying molecular-level interactions. Results demonstrate that an optimal PAAS/EMS mass ratio of 0.2 significantly enhances compressive strength (12.3-fold increase), reaching 2.78 MPa, and reduces the permeability coefficient to 1.318 × 10 −8 cm/s, with leachate concentrations meeting relevant water quality standards. This performance improvement stems from a synergistic multi-scale effect: macroscopically, well-dispersed PAAS forms a crosslinked network, filling structural defects within the EMR matrix and encapsulating the CaSO 4 ·2 H 2 O hard phase; at the molecular level, MD simulations reveal that PAAS chains undergo ion exchange (Na + with Mn 2+ ) and chelation (between -COO - and Mn 2+ ), forming a multi-crosslinked polymer network that densifies the microstructure and effectively impedes contaminant migration. FTIR and XPS analyses corroborate these molecular interactions, confirming that the enhanced impermeability arises from the synergistic effects of polymerization, ion exchange, and chelation. This study provides a new approach for controlling environmental risks associated with EMS, demonstrating the efficacy of multi-scale analysis in optimizing material performance.