Mechanism studies for adsorption and extraction of soluble sodium from bauxite residue: Characterization, kinetics, and thermodynamics

Abstract

Bauxite residue contains a certain amount of alkali metal ions, among which sodium ions are predominant and have a great impact on its application performance. In this paper, a series of sodium ion adsorbents with different Al contents were prepared based on the structural characteristics of NASICON-type materials to study the effect on sodium ion adsorption and regeneration adsorption performance. The results showed that the adsorbent with 40% Al had the best adsorption rate (95.6%). The adsorbents were characterized by SEM, XRD, Raman spectroscopy, TG-DSC, XPS and N2 adsorption-desorption, and the results showed that the adsorbents had a stable three-dimensional network structure. The adsorption isotherm models, adsorption kinetics and adsorption thermodynamics were discussed. The adsorption process followed the Langmuir isotherm model and pseudo-second-order kinetic model and was a spontaneous exothermic reaction. In addition, the adsorption mechanism was also discussed; this mechanism involved the participation of carbon-oxygen bonds and electrostatic interactions during adsorption. Desorption and regeneration experiments demonstrated that the adsorbent had excellent reusability, with an adsorption rate of 88.82% after three cycles. This study effectively solves the problem of sodium ion disposal in waste liquid after bauxite residue dealkalization to a certain extent, alleviating the environmental pollution caused by subsequent waste liquid discharge. Additionally, the later application of sodium ions can "turn trash into treasure". This study not only provides a new route for the separation of sodium ions in bauxite residue but also has great significance both from an environmental perspective and from a resource recovery perspective.