Process of phosphate removal in Fe0/H2O systems: A novel kinetic model considering iron corrosion at neutral pH

Abstract

• A kinetic model considering dynamics of Fe 0 corrosion is developed for Fe 0 /H 2 O systems • The model outperforms conventional kinetic models in describing phosphate removal • Iron corrosion is the rate-limiting step for phosphate removal in Fe 0 /H 2 O systems at neutral pH • Fe 0 -based systems are sustainable in long-term remediation due to continuous generation of iron corrosion products The development of a novel kinetic model that accounts for the dynamic generation of iron corrosion products (FeCPs) represents a significant advancement in understanding phosphate (PO 4 3– ) removal by metallic iron (Fe⁰). While Fe⁰ has been utilized as a reactive material for phosphate removal, existing studies have largely overlooked the critical role of in-situ generated FeCPs in the removal process. This study aims to address this gap by developing a kinetic model for phosphate removal in Fe 0 /H 2 O systems while considering the dynamic nature of Fe° corrosion or FeCPs generation under natural conditions (neutral pH ∼7, 25°C). It integrates Fe⁰ corrosion, FeCPs precipitation, and phosphate removal via adsorption, complexation, and precipitation. Batch experiments using 4.5 g/L Fe 0 , and an initial PO 4 3– concentration of 10.0 mg/L were conducted to validate the proposed kinetic model. The model achieved high fitting accuracy (R² = 0.90), capturing the unique "slow-start" phase of PO 4 3– removal. It outperforms pseudo-first-order (R² = 0.72) and pseudo-second-order (R² = 0.71) models. Sensitivity analyses confirm Fe⁰ corrosion, not chemisorption or diffusion, is the rate-limiting step. Long-term simulations (100 days) show that Fe⁰-based systems outperform conventional adsorbents due to continuous FeCPs generation. The model establishes a reliable predictive framework for designing and optimizing Fe⁰-based water remediation technologies.