Hydrogen Production from Zero-Valent Iron in Anaerobic Bicarbonate-Rich Media: The Role of Low-Dose Scrap Aluminum

Abstract Hydrogen (H2) production from zero-valent iron (ZVI) in bicarbonate-rich media is a promising low-temperature route, although progressive surface passivation remains a limitation. The influence of ZVI concentration (10–50 g/L), scrap aluminum (Al) addition, temperature (4–80 °C), sodium bicarbonate concentration (0–70 g/L NaHCO3), multi-cycle operation, and manual grinding was evaluated under anaerobic conditions. Temperature strongly affected kinetics, with an apparent activation energy of ∼30.8 kJ/mol for the ZVI–Al–bicarbonate system. The highest overall H2 yield approached 50% in the ZVI–Al system at 80 °C, substantially exceeding the yields obtained at lower temperature and in the absence of Al. Bicarbonate, especially above 30 g/L NaHCO3, played a critical role by sustaining proton availability through the bicarbonate/carbonate equilibrium and thereby promoting Fe corrosion and H2 evolution. The resulting progressive increase in pH created alkaline conditions that, in the presence of Al, further enhanced H2 generation. In multi-cycle experiments, manual grinding further improved performance by partially restoring reactivity, resulting in H2 yields approaching 50%. XRD analysis showed that siderite (FeCO3) remained the dominant Fe-bearing corrosion product, while Fe–Al layered double hydroxide, minor chukanovite, and aluminum hydroxide (Al(OH)3) were detected only in the presence of Al.