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Co-transport and interaction mechanisms of microplastics and Fe(III) in salt water-saturated porous media: Synergistic effects of competitive adsorption and blocking effect
Summary
Researchers used dynamic column experiments to examine the co-transport and interaction mechanisms of polystyrene microplastics and Fe(III) in saline, water-saturated porous media. They found competitive adsorption and blocking effects create synergistic behavior during co-transport, and combined a Two-Sites Kinetic Model with machine learning to accurately predict transport dynamics.
Synergistic contamination by microplastics (MPs) and Fe(III) has threatened sustainable groundwater utilization and environmental safety. However, the co-transport mechanisms governing MPs and Fe(III) in saline groundwater environments remain inadequately characterized. To address this, this study employed dynamic column experiments to reveal the microscopic mechanisms governing the interaction and co-transport of polystyrene (PS) MPs and Fe(III), and innovatively combined a Two-Sites Kinetic Model (TSKM) with machine learning (ML) for accurate prediction. Results demonstrated that PS and Fe(III) co-transport in saline environments followed the TSKM (R values exceeded 0.80), exhibiting mutual inhibition. The physical adsorption of Fe(III) onto PS during co-transport weakened surface electronegativity and promoted structural strain, which collectively enhanced the deposition of the Fe(III)-PS complexes. The transport capacity of PS increased with larger glass bead size, higher velocity, and greater aging, but decreased with larger PS size, elevated salinity, and higher Fe(III) concentration. Conversely, all factors except PS aging promoted Fe(III) transport, primarily due to competitive adsorption between Na and Fe(III), which led to enhanced mobility of Fe(III). Five ML models were developed to predict contaminant elution rates, with Gaussian Process Regression (GPR) exhibiting superior predictive performance (R values of 0.856 and 0.974 for PS and Fe(III), respectively). SHapley Additive exPlanations (SHAP) analysis identified glass bead size and velocity as the predominant predictors of PS and Fe(III) transport, respectively. This work elucidates co-transport mechanisms and controlling factors for PS and Fe(III) in saline groundwater, providing a critical theoretical framework for groundwater remediation and sustainable water resource management.