Nanoflakes of chloride zinc–iron–aluminum-based layered double hydroxides obtained from industrial waste: a green approach to mass-scale production

Abstract

A greener technology aiming at a smarter industrial waste treatment is proposed to produce chloride iron–zinc–aluminum layered double hydroxides (LDHs). Waste Pickling Acid (WPA) and sodium aluminate (NaAlO₂) from secondary sources were meticulously mixed under mild experimental conditions using a sodium hydroxide solution as a pH-regulator. A set of characterization techniques (XRD, SEM, TGA, FTIR, AAS and adsorption–desorption of N₂) indicated the formation of highly-dispersed nanoflake crystallites with textural characteristics and thermal stability similar to syntheses with high-quality chemicals. An interesting discussion on chemical composition and M²⁺/M³⁺ molar ratio is presented. Although the co-precipitation synthesis was conducted without control of environmental CO₂, complete intercalation of the chloride anion was achieved, making these particles more favorable for further anion exchange applications. The experimental variables temperature of reaction and WPA/NaAlO₂ volume ratio showed the strongest influence on the LDHs crystallinity and porosity. LDHs architected with iron and zinc have the potential to be applied in systems for removing sulfur gases for cleaner energy production, e.g. in the refining process of biogas to produce biomethane.