Waste to Hydrogen: Elaboration of Hydroreactive Materials from Magnesium-Aluminum Scrap

Abstract

Ball-milled hydroreactive powders of Mg-Al scrap with 20 wt.% additive (Wood’s alloy, KCl, and their mixture) and with no additives were manufactured. Their hydrogen yields and reaction rates in a 3.5 wt.% NaCl aqueous solution at 15–35 °С were compared. In the beginning of the reaction, samples with KCl (20 wt.%) and Wood’s alloy (10 wt.%) with KCl (10 wt.%) provided the highest and second-highest reaction rates, respectively. However, their hydrogen yields after 4 h were correspondingly the lowest and second-lowest percentages—(45.6 ± 4.4)% and (56.0 ± 1.2)% at 35 °С. At the same temperature, samples with 20 wt.% Wood’s alloy and with no additives demonstrated the highest hydrogen yields of (73.5 ± 10.0)% and (70.6 ± 2.5)%, correspondingly, while their respective maximum reaction rates were the lowest and second-lowest. The variations in reaction kinetics for the powders can be explained by the difference in their particle sizes (apparently affecting specific surface area), the crystal lattice defects accumulated during ball milling, favoring pitting corrosion, the morphology of the solid reaction product covering the particles, and the contradicting effects from the potential formation of reaction-enhancing microgalvanic cells intended to induce anodic dissolution of Mg in conductive media and reaction-hindering crystal-grain-screening compounds of the alloy and metal scrap components.

Microstructural Transformation and Hydrogen Generation Performance of Magnesium Scrap Ball Milled with Devarda’s Alloy

“…As it has been mentioned above, the ML5 grade alloy is generally similar to the AZ91D alloy, which is composed mainly of α-phase Mg and β-phase Mg17Al12 [95]. According to the preceding paper [66], the identification of the Al phase was associated with the enrichment of the Mg17Al12 phase with aluminum after a thermal treatment (homogenization at 420 °С for 12 h and aging at 200 °С for 8 h), standard for the ML5 alloy. In report [96], the content of Mg17Al12 in an ML5 alloy sample was 5.31 wt.%, with the content of Al in the Mg17Al12 phase achieving as much as 3.42 wt.% of the total mass.…”

“…The most extensively investigated ones include high reaction temperatures (above 100 • C) [25][26][27][28][29][30][31][32], various acidic [33][34][35], alkali (for aluminum) [36][37][38][39] and salt (NaCl, KCl, MgCl 2 , NiCl 2 , CoCl 2 , CuCl 2 , AlCl 3 ) [40][41][42][43][44][45][46][47][48] solutions, liquid metal embrittlement (for aluminum) [49][50][51], alloying with metals like Ca, Ni, Sn, Fe, Li, Zn, Bi, Cu (brand-new or recovered from electronic and electrical waste) [52][53][54][55][56][57][58][59][60][61], preparation of composite powders with metal (Ni, Nd, Bi, Zn, In, Wood's alloy, etc.) [62][63][64][65][66], and non-metal (e.g., NaCl, AlCl 3 , Bi 2 O 2 CO 3 , Bi(OH) 3 , Al(OH) 3 , Al 2 O 3 ) [67][68][69] additives, or their mixtures (e.g., carbon materials with Bi, Ni, Cu, Co, MgCl 2 , AlCl 3 , Ga-based eutecti...…”

“…Summarizing the abovementioned, magnesium waste chips, shavings, and cuts have good potential for hydrogen generation. In a preceding comparative study [66], waste material samples were activated by ball milling (4 h) with 20 wt.% additives (KCl, Wood's alloy, and their combination) and without additives and reacted with 3.5 wt.% NaCl aqueous solution. Unexpectedly, the highest specific hydrogen yields corresponded to the sample without additives, although it had the largest particles.…”

Productive and Sustainable H2 Production from Waste Aluminum Using Copper Oxides-Based Graphene Nanocatalysts: A Techno-Economic Analysis

“…Aluminum is the most abundant metal on earth, with facile and low-cost processing. It has the densest potential H 2 storage capacity among all other metals, with a theoretical capacity of ~1350 mL H 2 per g of Al, under atmospheric conditions [17,18]. Furthermore, based on the theoretical calculations, 1 kg of low-cost waste aluminum can generate 4 kWh of electricity.…”

“…This process could be considered a sustainable starting material for the bulk energy production of H 2 [19]. Consequently, extensive research studies and industrial developments have been attempted for efficient and feasible H 2 production from Al precursors [17][18][19]. The continuous synthesis of H 2 from Al-H 2 O is a straightforward and sustainable reaction, especially in base and acid environments [20][21][22][23].…”