Dual-functional remediation of ammonia nitrogen contamination in ionic rare earth mines: Efficient washing and soil stabilization using lignosulfonates

Ammonia nitrogen (NH₄⁺-N) pollution from in-situ leaching of ionic rare earth mines poses severe ecological risks, including soil acidification and groundwater contamination. This study proposes a novel dual-functional strategy using lignosulfonates—calcium lignosulfonate (CLS) and sodium lignosulfonate (SLS)—to simultaneously remove NH₄⁺-N and stabilize soil structure. Batch and column experiments revealed that CLS achieved 82.59% NH₄⁺-N removal (compared to 47.22% by water washing) from simulated contaminated soil, while SLS showed 85.11% efficiency. Kinetic modeling using the Elovich and Two-constant equations ( R ² = 0.910–0.941) indicated that NH₄⁺-N removal was primarily governed by heterogeneous diffusion and cation exchange processes. CLS outperformed SLS in soil stabilization, increasing shear strength by 114% and reducing soil porosity by 49.40% through particle aggregation. Field-collected soil experiments validated CLS's robust performance, achieving >91% removal of exchangeable NH₄⁺-N while maintaining a neutral pH (7.54 compared to SLS-induced pH 10.08), avoiding secondary alkalization risks. Mechanistic analysis highlighted Ca²⁺-mediated ion exchange, electrostatic interactions with sulfonic groups, and hydrogen bonding as key pathways. This work provides a sustainable solution leveraging industrial byproducts (lignosulfonates) for eco-friendly mine remediation, aligning with circular economy principles. • Lignosulfonates remove >85% NH₄⁺-N & stabilize soil in rare earth mines • CLS retains neutral soil pH (7.25–7.54), avoiding SLS-induced alkalization (pH 10.08). • Only 1.67 mg/L NH₄⁺-N was leached out by simulated rainfall after treated with CLS. • Ca²⁺ exchange/sulfonic groups dominate NH₄⁺-N removal. • Lignosulfonates: low-cost paper waste upcycled for eco-friendly mine remediation.