715 metallic titanium at sufficiently low oxygen partial pressures and high temperatures. This reduction proceeds via stepwise oxygen removal controlled by thermodynamic stability boundaries in the Ti-O system, with intermediate Magnéli phases forming as oxygen vacancies increase (Wu et al., 2023; Liu et al., 2018; Ekanayake et al., 2025). However, such transformations require strongly reducing atmospheres and elevated temperatures, typically exceeding those applied in the present experimental conditions. Consequently, titanium remains stabilized in oxidized mineral phases within the investigated processing window, consistent with the absence of reduced titanium phases in the experimental observations. The presence of larnite (β-Ca₂SiO₄) is particularly significant, as it is a well-known hydraulic phase and the principal constituent of belite-rich cements. Upon hydration, larnite reacts with water to form calcium silicate hydrate (C-S-H) and calcium hydroxide, contributing to strength development and long-term durability, albeit with slower kinetics compared to alite (Taylor, 1997; Hewlett & Liska, 2019). Its occurrence in industrial residues such as metallurgical slags and BR therefore represents an intrinsic latent binder potential that can be utilized without the need for energy-intensive clinker production (Snellings et al., 2012; Stopic et al., 2024). From a circular economy perspective, valorising larnite-bearing residues as supplementary binder components provides a direct pathway to circularity, “closing the material loop”, reducing clinker demand, lowering CO₂ emissions, and transforming metallurgical by-products into functional cementitious resources (Scrivener et al., 2018; Provis & van Deventer, 2014). The thermodynamic modelling significantly reduced the experimental design space and enabled a more efficient and targeted experimental approach. Rather than exploring a broad and largely unconstrained range of temperatures and atmospheres through empirical trial-and-error, the modelling provided clear guidance on the temperature and oxygen fugacity conditions most favourable for achieving the desired phase transformations. This allowed experimental efforts to focus directly on the predicted optimal reduction window, followed by fine-tuning of process parameters such as treatment time and gas flow. As a result, unnecessary experiments under thermodynamically unfavourable conditions were avoided. This targeted approach offers substantial practical benefits. By reducing the number of exploratory experiments required, the modelling minimizes the consumption of energy, materials, and laboratory resources. It also accelerates the development cycle by enabling faster convergence toward optimal processing conditions. This is particularly important for industrial-scale applications, where energy efficiency and process optimization are critical for economic and environmental sustainability. Furthermore, the use of freely available thermodynamic modelling tools such as Perple_X democratizes access to advanced process design capabilities, enabling research laboratories with limited experimental infrastructure to efficiently design and optimize reduction processes. Overall, the agreement between thermodynamic predictions and experimental results confirms the reliability of the modelling approach and highlights its value as an effective tool for accelerating the development of sustainable recovery processes for iron and titanium from BR and other complex industrial residues. 5. CONCLUSIONS This study demonstrates that thermodynamic modelling using Perple_X provides a powerful, efficient and freely available computational tool to accelerate the responsible recovery of critical raw materials from industrial residues such as BR. The calculated phase stability diagrams identified a clear reduction window in which iron-bearing oxides are transformed into metallic iron, while titanium is preferentially concentrated into perovskite, a phase favourable for downstream recovery. Experimental validation confirmed these predictions, demonstrating high iron metallization and effective titanium partitioning. The strong agreement between modelling and experimental results confirms that thermodynamic tools can reliably guide process design and material valorization strategies. Beyond the specific system studied, this work highlights how modelling can significantly reduce the experimental design space, enabling targeted process optimization rather than relying on resourceintensive trial-and-error approaches. By focusing directly on thermodynamically favourable conditions, the development cycle is accelerated while reducing energy consumption, material use, and associated environmental impact. This smarter and more efficient approach directly supports the global need to deliver essential minerals faster and more responsibly.
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