Salicylic acid-induced single-step synthesis of multimorphic anhydrous MgCO3 from brucite waste: Characterization, mechanism, and DFT calculation

Abstract

The brucite production generates a large amount of powdered solid waste, which presents significant challenges for direct utilization. Utilizing brucite for CO₂ mineralization enables solid waste reuse and CO₂ utilization and storage. In this study, multimorphic anhydrous MgCO₃ was synthesized from brucite solid waste and salicylic acid using a one-step method. The results indicate that higher temperatures and longer hydrothermal times favor the anhydrous MgCO₃ formation. Cubic, hexagonal block and columnar anhydrous MgCO₃ were synthesized by regulating the salicylic acid additions. The formation mechanism reveals that coordination between salicylic acid and Mg²⁺ inhibits Mg²⁺ hydration, preventing the hydrated MgCO₃ formation. Phenol and phenolate anion derived from salicylic acid decomposition adsorb onto the anhydrous MgCO₃ surfaces, regulating crystal growth. Characterization results and DFT calculations show that the salicylate, phenolate anion, and phenol form ionic coordination bonds and hydrogen bonds with Mg²⁺/anhydrous MgCO₃, achieving chelation and adsorption, which modulate the phase transition and morphology of crystal. Anhydrous MgCO₃ shows potential applications in flame retardancy, electronic component enhancement, photoelectrochemical energy storage, and wastewater treatment. This method represents a comprehensive green technology for CO₂ reduction and anhydrous MgCO₃ synthesis, shortening the preparation process for high-value-added magnesium products, and offering broad industrial prospects.