Hydrogen (H2) was produced from recycled aluminum microparticles (180–250, 300–425, and 425–500 μm) via alkaline hydrolysis using a 1.0 M NaOH solution to enhance oxide layer removal and aluminum dissolution. Maximum hydrogen flow rates of approximately 13, 15, and 19 mL·min−1 were obtained, confirming that smaller particle sizes promote faster reaction rates due to increased specific surface area. The hydrogen evolution exhibited two-stage kinetic behavior: an initial stage characterized by rapid aluminum dissolution and increasing H2 production, followed by a gradual decline associated with the formation of a passivating Al(OH)3 layer. Despite the higher reaction rates observed for smaller particles, the maximum cumulative hydrogen production was obtained for the intermediate particle size (363 µm, 132 mL), compared to 106 mL and 102 mL for 215 µm and 463 µm, respectively, indicating a trade-off between surface area and passivation effects. Kinetic analysis based on the shrinking core model showed excellent agreement (R2 = 99.94–99.97%), with rate constants of 0.137, 0.064, and 0.050 min−1. The relationship k ∝ d−n (n ≈ 1.4) suggests a mixed kinetic regime involving both surface reaction and diffusion through the Al(OH)3 layer. These findings indicate that hydrogen generation can be modulated by particle size; however, the relatively low flow rates and yields limit its immediate practical applicability.
Martínez-Vargas et al. (Wed,) studied this question.