Hydrogen-Rich Gas Produced by the Chemical Neutralization of Reactive By-Products from the Screening Processes of the Secondary Aluminum Industry

In the framework of the industry of secondary aluminum, the chemical neutralization ofhighly reactive materials that come from the pre-treatment screening processes of scraps (beveragecans and domestic appliances) was investigated through experiments in aqueous alkaline solutions.Metallic aluminum-rich by-products are classified, according to EU law, as dangerous waste, as theycan potentially develop flammable gases capable of forming explosive mixtures with air. In this waythey cannot be disposed of in landfills for non-hazardous wastes if chemical neutralization is notplanned and performed beforehand. In this way, these experiments were mainly aimed at unravelingthe oxidation rate and at quantifying the production of hydrogen-rich gases from the reactions of themetallic aluminum-rich by-products in a water-rich alkaline (liquid or vapor) environment. Reactionswere carried out in a stainless-steel batch mini-reactor with metering and sampling valves, with theresulting gases analyzed by gas-chromatography (GC). The experimental setup was planned to avoidthe following issues: (i) the corrosion of the reactor by the alkaline solution and (ii) the permeabilityof the system to hydrogen (i.e., possible leaks of H2), related to the fast kinetics and short duration ofthe reactions (which may hinder a pile-up-effect) between the solid by-products and the liquid. Theprocedure was defined by a controlled interaction process between metals and liquid, using NaOHto increase reaction rates. The experimental runs performed in the mini-reactor proved to be effectivefor eliminating the reactive metallic aluminum, reaching a maximum hydrogen production of 96% ofthe total gases produced in the experiments. The relations between gas generation (up to 55 bar of H2in the experiments, which lasted for four days) and each specific parameter variation are discussed.All the obtained results can be transferred and applied to (i) the possible industrialization of themethod for the chemical neutralization of these dangerous by-products, increasing sustainabilityand workplace safety, (ii) the use of the resulting hydrogen as a source of energy for the furnacesof the secondary aluminum industry itself, and (iii) new technological materials (e.g., "foamedgeopolymers"), by using hydrogen as a foaming agent, coupled with aluminosilicate materials,during geopolymeric reactions.