709 In this work, we are focusing on the use of thermodynamic modelling to guide process development. Rather than rely solely on empirical trial-and-error (which can be costly and time-consuming given the high temperatures and caustic materials involved), the consortium employed advanced equilibrium modelling tools to predict how BR and titania slag will behave during reduction and leaching. In particular, the Perple_X software (Connolly, 2005) was used to calculate stable phase assemblages’ fields as a function of temperature, pressure, and oxygen fugacity for the complex multi-oxide composition of these residues. This approach allowed to forecast mineral phase evolution under various scenarios, for example, identifying the temperature at which iron oxides would reduce to metal, or whether titanium would remain as TiO₂, form CaTiO₃ perovskite, or reduce to metallic Ti or carbides under certain conditions. In previous research performed, complementary equilibrium calculations were performed using FactSage™ for selected reactions (Stopic et al., 2024). The use of Perple_X (an open-source thermodynamic modelling software traditionally applied in geosciences) represents a new opportunity. Its accessibility reduces resource requirements and enables laboratories with limited equipment and computational budgets to integrate thermodynamic modelling into experimental design and optimization. This paper presents the context and goals of EURO-TITAN, details how thermodynamic modelling can be applied to optimize the recovery of Ti and Fe, and discusses key results, including the identification of desirable Ti-bearing phases (e.g. perovskite) that facilitate downstream extraction. The outcomes of this study offer insights into sustainable raw material recovery and can inform similar efforts for other critical materials. 2. METHODOLOGY AND MODELLING APPROACH Figure 1 outlines the EURO-TITAN flowsheet. In the first step, the waste feed is subjected to hydrogen-based reduction at high temperature. Two complementary reduction routes are being explored: (1) a rotary kiln or tubular furnace for direct H₂ reduction of the dried residue in solid state, and (2) an electric arc furnace (EAF) assisted by hydrogen-plasma, which melts the material (at ~1500 °C) and providing a reducing H plasma. In either case, the goal is to reduce iron (III) oxides (Fe₂O₃/Fe₃O₄) to metallic iron (Fe⁰) while keeping titanium in an oxidized form (Ti⁴⁺ as TiO₂ or CaTiO₃). The reduced material is then cooled and the iron separated, either by magnetic separation (if iron remains as dispersed metallic granules in a solid slag matrix, or by melt separation (tapping off liquid titanium-rich slag if an EAF smelting operation). The separated crude iron is a valuable by-product, usable in steelmaking or foundries, containing minimal Ti or other contaminants in the optimized conditions (Stopic et al., 2025). The remaining Ti-rich slag (depleted in Fe) is then treated hydrometallurgically: it is leached in hot acid (e.g. sulfuric acid under pressure) to dissolve the titanium values into solution (as titanyl sulfate, TiOSO₄, or related complexes). The leaching conditions are tuned to avoid silica gel formation and maximize Ti extraction, benefitting from the slag’s mineralogy, which the modelling helps to optimize (discussed below). After purification of the leachate, the titanium is recovered either as TiO₂ or directly as a precursor (e.g. Ti-oxysulfate solution) which is converted to powder. EURO-TITAN employs ultrasonic spray pyrolysis (USP) to produce spherical TiO₂ particles from the purified solution (Fig. 1). The entire process will be powered by renewable energy (electrolytic H₂, electric furnaces), targeting about 90% reduction in CO₂ emissions relative to carbothermic routes (www.EURO-Titan.eu). Departing from the BR residue, and to help understand the thermodynamic system from the beginning, equilibrium phase modelling was performed. In this work, we use the Perple_X suite (Connolly, 2005) to calculate phase stability as a function of T, P, oxygen fugacity and chemical conditions for our feed materials. Perple_X enables construction of phase diagrams (P-T, T-Log fO2, chemistry, etc.) for multicomponent systems by minimizing Gibbs free energy for given bulk compositions. Direct H2 reduction experiments are currently being conducted to evaluate the phase transformation and metal recovery potential of the BR. The tests are performed using 4 g of BR per experiment at temperatures ranging from 700 to 1100 °C, with treatment durations between 15 and 180 minutes. A controlled gas flow of 100 to 500 L/h is applied using a gas mixture consisting of 10 vol.% hydrogen balanced with nitrogen, under atmospheric pressure. These conditions are designed to systematically assess the
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