Atmospheric pressure preparation of ammonioalunite for highly efficient fluoride removal

Abstract

Ammonioalunite (NH₄Al₃(SO₄)₂(OH)₆) is well known as an inorganic mineral which can be applied in various fields such as sewage treatment, ceramics and catalysis. To date, the hydrothermal approach is prevalently employed for the synthesis of ammonioalunite. Nevertheless, this method entails significant costs and imposes rigorous demands. Furthermore, no research efforts have been dedicated to exploring the performance characteristics of ammonioalunite up to this point. This paper puts forward a new method for synthesizing ammonioalunite under atmospheric pressure conditions, and the method is of low cost and simple to operate. The synthesized ammonioalunite was utilized as an adsorbent for the eradication of fluoride ions from aqueous solutions for the first time. The as-synthesized ammonioalunite possesses an adsorption capacity of 77.41 mg g⁻¹ and presents outstanding regenerative capabilities, maintaining a fluoride removal efficiency of 85.16% even after six regeneration cycles. The computed outcomes of thermodynamic parameters manifest that the process of fluoride ion adsorption by ammonioalunite is a spontaneously occurring endothermic reaction. The adsorption effect of ammonioalunite is more favorable under acidic conditions. The coexisting anion PO₄³⁻ has a negative impact on the adsorption performance. And the adsorption mechanism is mainly ascribed to ion exchange and hydrogen bonding for the removal of fluoride. This research demonstrates that highly crystalline ammonioalunite can be prepared at atmospheric pressure and is capable of functioning as a highly practicable and efficacious adsorbent for the elimination of fluoride ions from aqueous solutions.