Simplified kinetics model for hydrogen gas generation from metallic aluminum in municipal solid waste incineration bottom ash

The reaction of metallic aluminum in the incineration bottom ash (IBA) with an alkaline medium generates hydrogen (H₂) gas. The generated H₂ has caused severe cracking when IBA is used as construction material. Studies have then explored applications of IBA in aerated concretes where H₂ from metallic aluminum can be utilized advantageously and found that the kinetics of H₂ generation influence the cellular structure and mechanical properties. However, no kinetics model is available to understand the reaction kinetics of H₂ gas generation from IBA. This study presents a simplified kinetics model employing the shrinking core model for H₂ generation from metallic aluminum in IBA. The uniform distribution of metallic aluminum in IBA particles and average particle size were considered to make the model simplified for practical applications. The model was calibrated by the hydrogen gas generation from IBA and a known alkaline solution (NaOH). The temperature dependency of the reaction rate was implemented using the Arrhenius equation. The study showed that the hydrogen gas generation in IBA demonstrated reaction control kinetics at higher temperatures (≥ 60 °C) and diffusion control kinetics at lower temperatures (≈ 25 °C). The yield of hydrogen gas generation also decreased with the reduction in reaction temperature. The kinetics model was successfully validated against the experimental data for the local IBA. The presented model is expected to improve the understanding of dynamic H₂ gas generation from metallic aluminum in IBA and guide the development of aerated composites with target properties where IBA is used as an aerating agent.