Effective hydrogen production by hydrolysis of Mg wastes reprocessed by mechanical milling with iron and graphite

Abstract

The reprocessing by mechanical milling of Mg scraps from the manufacturing of sacrificial anodes to produce H2 by hydrolysis is discussed. In particular, the effects of iron and graphite as additives to improve the hydrolysis reaction are presented. It has been found that by pre-milling the scraps under air atmosphere for 10 h with 1.5 wt% of Fe followed by an extra milling of 1 h with 5 wt% of graphite produces the best results. Fe contributes to speed up the reaction rate by inducing microgalvanic coupling with Mg, and graphite plays a significant role as process control agent during milling inducing a significant size reduction of the material. As the shape of the hydrolysis curves is compatible with a kinetic process controlled by volume contraction, the acceleration of the movement of the Mg/Mg(OH)2 interphase induced by the galvanic coupling, and the reduction in size both contribute to a faster H2 production. Additionally, the performance of the material favorably compares with similar materials reported in the literature producing 775 mL/g of H2 in 5 min, and 780 mL/g when the reaction finishes (84 % yield).