**Thermodynamics of FeO Oxidation in Dephosphorization during Basic Steelmaking: A Critical Review of Reaction Models, Slag Chemistry, and Equilibrium Limitations**
Year: 2026
Type: preprint
Abstract: ### **Alternative Titles**1. **The Dual Role of FeO in Dephosphorization: Thermodynamic Constraints, Slag Basicity, and Kinetic Realities in Basic Oxygen Furnace Steelmaking**2. **From Molecular to Ionic Models: A Thermodynamic Analysis of FeO-Driven Phosphorus Removal in Basic Steelmaking**3. **Slag Chemistry and Equilibrium Limitations in Dephosphorization: The Critical Function of FeO Oxidation in BOF Refining** ### **Subtitle***A comprehensive thermodynamic analysis of the FeO-driven oxidation of phosphorus in basic steelmaking, examining molecular and ionic reaction models, the dual function of FeO as an oxidant and slag fluidizer, the constraints imposed by basicity and temperature, and the gap between equilibrium predictions and industrial BOF practice.* --- ### **Detailed Description** **Overview:**This research paper provides a critical review of the thermodynamic principles governing dephosphorization in basic steelmaking, with a specific focus on the role of FeO as the primary oxidizing agent. Phosphorus is a highly deleterious element in steel, causing cold shortness and degrading mechanical properties even at concentrations as low as 0.01–0.02 wt%. Its removal is achieved through oxidative refining in processes such as the Basic Oxygen Furnace (BOF), where dissolved phosphorus is oxidized by FeO and subsequently stabilized in a basic slag as calcium phosphate. The paper synthesizes classical and contemporary thermodynamic models to elucidate the coupled chemical and physical factors that control this critical refining step. **Key Themes & Findings:** - **Reaction Representations—Molecular vs. Ionic Models:** The paper examines the evolution of dephosphorization equations, from simple molecular formulations (2[P] + 5(FeO) ⇌ (P₂O₅) + 5[Fe]) to more accurate ionic representations ([P] + 5/2(FeO) + 3/2(O²⁻) ⇌ (PO₄³⁻) + 5/2Fe). The ionic model correctly reflects that phosphorus enters the slag as a phosphate anion (PO₄³⁻), requiring both oxygen potential from FeO and free oxygen ions from CaO for stabilization. - **The Dual Function of FeO:** A central contribution of this review is the clarification of FeO's dual thermodynamic role. First, FeO controls the oxygen potential at the slag–metal interface, directly driving phosphorus oxidation. Second, FeO acts as a network modifier in the silicate melt, breaking Si–O–Si bonds to improve slag fluidity and enhance mass transfer kinetics. The interplay between these two functions is critical for optimizing dephosphorization efficiency. - **Thermodynamic Constraints—Basicity and Temperature:** The paper analyzes the influence of slag basicity (CaO/SiO₂ ratio) and temperature on phosphate capacity. While higher basicity enhances the slag's ability to stabilize phosphate species, excessive basicity increases liquidus temperature and viscosity, impairing kinetics. Lower temperatures thermodynamically favor phosphorus oxidation (the reaction is exothermic), but higher temperatures improve slag fluidity—creating a practical operating window that balances thermodynamic favorability with kinetic feasibility. Empirical correlations, such as the Suito/Ide-Fruehan models, are discussed as tools for predicting phosphorus partition ratios under industrial conditions. - **Equilibrium Limitations in Industrial Practice:** The paper critically examines the gap between equilibrium thermodynamic predictions and actual industrial performance. Industrial phosphorus partition ratios are often far from equilibrium and vary with blowing practice, stirring intensity, and converter life. The timing of dephosphorization within the BOF blow—optimal during early and middle stages when FeO is rising and temperature is moderate—and the risk of phosphorus reversion during tapping are analyzed through recent kinetic and tapping models. - **Implications for Process Design:** The thermodynamic analysis yields practical recommendations: maintaining FeO within an optimal range to balance oxygen potential and slag fluidity; controlling basicity to avoid high liquidus temperature regimes; and managing temperature to prevent excessive superheat in later refining stages. The paper also highlights the growing use of thermodynamic modeling software (e.g., FactSage) for multi-constraint slag design, enabling the screening of feasible compositions before industrial trials. **Conclusion:**The paper concludes that while the fundamental thermodynamics of FeO-driven dephosphorization are well established, the persistent gap between equilibrium predictions and industrial performance underscores the critical importance of kinetic and process-dynamic factors. Future advances in dephosphorization efficiency will depend not on further refinement of equilibrium descriptions alone, but on the integration of thermodynamic databases with kinetic models and real-time process control strategies for the BOF.
Author: geruganti, sudhakar
Language: English
Subfield: Metals and Alloys
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7225575297