Geochemical remediation and spectral induced polarization monitoring of Cu2+ by geographically abundant paleosol and loess

Copper (Cu²⁺) contamination is a critical environmental issue stemming from industrial activities. This study evaluates the remediation potential of paleosol and loess, two geologically abundant aeolian soils, for Cu²⁺ contamination, with real-time monitoring via spectral induced polarization (SIP). Column breakthrough experiments demonstrated high Cu²⁺ retention capacities (1.49 mmol/g for paleosol and 1.72 mmol/g for loess, corresponding well with retention capacities obtained from the reactive transport modeling), outperforming commercial materials like activated carbon and biochar. Mechanistic analyses (scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and mercury intrusion porosimetry (MIP)) revealed that calcite dissolution drives Cu²⁺ hydrolysis and precipitation as the primary remediation pathway, with Mg²⁺ exchange playing a secondary role. The Cu²⁺ hydrolysis and precipitation remediation mechanism was further proven by the geochemical modeling (speciation and saturation indices). SIP monitoring exhibited strong correlations (R² > 0.77) between normalized chargeability (m_n) and Cu²⁺ adsorption, confirming SIP as an effective tool for real-time, non-invasive tracking of contaminant barriers. Compared to commercial adsorbents, paleosol and loess offer superior retention capacities, minimal production costs, and negligible carbon emissions. These findings position aeolian soils as sustainable, cost-efficient, and high-performance alternatives for addressing widespread heavy metal pollution.