Reprocessing different Mg-alloy wastes for hydrogen production by hydrolysis

Abstract

The increasing demand for sustainable hydrogen production and effective waste management underscores the importance of developing efficient methods for utilizing Mg-based alloy waste. This study applies a recently developed reprocessing scheme to generate hydrogen through the hydrolysis of various Mg-based alloy scraps, simultaneously addressing environmental concerns related to waste disposal. Our approach employs low-cost, non-polluting additives and demonstrates robust performance across three distinct alloys: shavings from the manufacturing of sacrificial anodes (AZ31 alloy) mixed with Al chips, shavings from the machining of automotive parts (AZ91 alloy) and chips from the manufacturing of aerospace industry components (Elektron 21 alloy). Mechanical milling of these scraps with the addition of 1.5 wt% Fe and 5 wt% C (graphite) significantly enhances reactivity, achieving hydrogen yields greater than 75% in 4 min when reacting in a 0.6 M MgCl2solution at room temperature. Characterization through X-ray diffraction, scanning electron microscopy, particle size analysis and hydrolysis experiments together with a model proposed to systematize the influence of different parameters on the hydrolysis performance reveals that C reduces cold welding during milling and greatly reduces particles size, Fe acts as a catalyst by forming galvanic pairs with Mg, the intermetallic compound Al12Mg17 favors hydrolysis and Al dissolved as a solute in Mg impairs it. This successful application across different alloys demonstrates the robustness of the reprocessing scheme and its potential for recycling a broader range of Mg-based wastes, contributing to both hydrogen production and environmental sustainability.