Investigation of γ-Polyglutamic Acid for Heavy Metal Decontamination from Coal Gangue-Based Soil: Quantum Chemical Analysis and Experimental Investigation

Heavy metal pollution from coal gangue severely degrades mine soil structure and threatens landscape ecological stability. Particularly, γ-polyglutamic acid (γ-PGA), a green biopolymer, offers potential applications for pollution remediation while supporting ecological restoration. To evaluate γ-PGA’s efficacy in immobilizing Pb, Cd, and Zn in gangue-based soil and clarify its regulatory mechanism for landscape-friendly remediation, soil samples from a 3-year-weathered gangue hill in the Liupanshui mining area were subjected to indoor leaching experiments with different γ-PGA doses, combined with material characterization and Density Functional Theory (DFT) simulations. The results showed that the optimal γ-PGA dose was 6 g/kg, achieving 93.25% Pb immobilization and reducing Cd/Zn migration risk by over 30%; γ-PGA acted via carboxyl-amide dual-site chelation and hydrogen-bonded agglomeration, forming stable aggregates that inhibited metal migration. DFT calculations confirmed strong chelation for Cu2+ (−59.54 kcal/mol, BSSE-corrected: −57.23 kcal/mol), while Pb2+ and Cd2+ showed weaker binding (−8.32 kcal/mol and −5.67 kcal/mol, BSSE-corrected: −6.15 kcal/mol and −3.89 kcal/mol, respectively), indicating multi-pathway immobilization mechanisms. This study provides a theoretical basis for applying γ-PGA in mine landscape ecological restoration.