Hydrolysis and neutralization processes of hydroxy sodalite

Kutus, Bence and Asher, Meerab and Kovács, Izabella and Sipos, Pál Miklós (2024) Hydrolysis and neutralization processes of hydroxy sodalite. In: 12th Alumina Quality Workshop, 2024.04.22-2024.04.24, Dubai.

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Abstract

Being one of the reactive phases present in bauxite residues, the dissolution of hydroxy sodalite or HXS, Na8[AlSiO4]6(OH)2∙mH2O, gives rise to a strongly alkaline environment in residue slurries. To effectively decrease the environmental hazards of bauxite residue via acid neutralization, it is pivotal to understand the neutralization mechanism as well as dissolution processes of HXS. To this end, we synthesized HXS and studied its hydrolysis as well as neutralization reactions using hydrochloric acid. We find that increasing the solid:liquid mass ratio results in a significant increase in the pH and dissolved metal concentrations, evidencing the incongruent dissolution of HXS. The secondary phases forming during this process are two types of hydrosodalite (HS1 and HS2), being dominant below pH ~ 10. Upon addition of HCl, the pH readily drops to ~7, suggesting rapid neutralization kinetics. Concomitantly, HXS transforms to HS1, giving rise to a slow increase in pH, before reaching a steady-state value of ~10.3.

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