Lanthanum-Modified Steel Slag for Phosphate Removal: Adsorption Mechanism, Leaching Safety, and Scalability

Articles in Press

Document Type : Original Research Paper

Authors

Department of Environmental Engineering, Faculty of Environment, University of Tehran, P.O. Box 14155-6619, Tehran, Iran

10.22059/poll.2025.401787.3101

Abstract

Phosphorus eutrophication threatens freshwater ecosystems and food security in semiarid agricultural regions. The potential of low-temperature (<400 °C) lanthanum modification of steel slag to achieve high adsorption capacity, environmental safety, and regenerability for phosphate removal is uncertain. We synthesized lanthanum-modified steel slag at 400 °C and conducted structural characterization. We performed batch and fixed-bed column adsorption tests, supplemented by the USEPA Method 1312 leaching assessment across pH 2–9, five-cycle regeneration studies, Visual MINTEQ geochemical modeling, and ISO 14044-compliant life-cycle cost analysis. The material showed a phosphate adsorption capacity of 3.21 ± 0.08 mg P/g at pH 7, a 90% improvement over pristine slag, maintained ≥80% performance across pH 5–9, and demonstrated lanthanum release of 0.0181 ± 0.0009 mg/L at pH 2—90.5% below regulatory guidelines and the lowest for rare-earth adsorbents. The five-cycle regeneration process retained 82 ± 2.1% of its capacity. Geochemical modeling revealed a dual-pathway mechanism: 60% reversible inner-sphere complexation and 40% irreversible lanthanum phosphate precipitation, accounting for superior performance. The manufacturing cost was USD 1.19 ± 0.12/kg, 60–70% lower than conventional rare-earth synthesis, yielding a net present value of USD 0.47 million and a 23.6% internal rate of return over ten years. This study established quantified design principles for low-temperature rare-earth adsorbents, facilitated decentralized phosphorus recovery in resource-limited regions, and demonstrated unprecedented lanthanum immobilization through triple-mechanism passivation combined with regenerability and economic viability in smallholder agricultural systems.

Keywords

Main Subjects

Pollution

Articles in Press, Accepted Manuscript
Available Online from 21 December 2025

Files

Share

How to cite

Statistics