Orange hydrogen production with fayalite slag: identifying reaction bottlenecks
Year: 2026
Type: preprint
Abstract: Orange hydrogen (H2) is generated through stimulated water–rock reactions, analogous to natural hydrogen formation via serpentinization, and offers a potential pathway for clean H2 production from Fe(II)-bearing minerals and mineral side streams. Here, we investigate orange H2 production based on fayalite slag, an Fe(II)-rich metallurgical waste that has not previously been studied for this purpose. H2 generation from fayalite slag was evaluated in a stirred hydrothermal reactor pressurized with Ar and experiments were carried out at initial pressures of 5, 50, and 100 bar and temperatures of 160 and 230 °C. The highest H2 production was observed at 230 °C and an initial pressure of 5 bar in 1 M KOH (pH 14) after 48 h, reaching 0.45 g H2 kg-1 fayalite slag, corresponding to ⁓7.2% of the theoretical maximum H2 yield. During the reaction, the fayalite content decreased, while magnetite and a K-bearing mica phase formed as secondary products. These secondary phases may have limited further reaction by reducing water access to Fe(II)-bearing regions. This is evidenced by the fact that H2 generation plateaued after 48 h of reaction time. Overall, the results show that fayalite slag is a potential feedstock for orange H2 production under comparatively mild hydrothermal conditions, while also indicating that secondary phase formation and surface passivation are important reaction bottlenecks.
Source: ChemRxiv
Institution: University of Oulu
Language: English
Subfield: Environmental Engineering
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7213975776