Bromate removal from aqueous solution with novel flower-like Mg-Al-layered double hydroxides

Abstract

A series of flower-like Mg-Al-layered double hydroxides (FHMA) with four Mg/Al ratios were successfully prepared via a simple method which put the mixed solution of magnesium and aluminum in the mixed solution of water and ethylene glycol (EG). After calcination under 600 °C, the calcination products (CFHMA) were used to adsorb bromate anionic from aqueous solution. The FHMA, CFHMA, and reconstructed CFHMA were characterized by FT-IR, XRD spectra, TG/DTA, N₂ adsorption-desorption isotherm, and SEM. It was found that FHMA had the flower-like morphology when Mg/Al ratio was 2 and 3. Moreover, FHMA lost the layered structures during calcination under 600 °C, but the disappeared structures were reconstructed after adsorption of bromate anionic, which was attributed to the "reformation effect" of FHMA with bromate as an interlayer anion. A series of adsorption studies were performed and the mechanism and reactivity of CFHMA were discussed including the effect of different kind of equilibration conditions, such as initial bromate anionic concentration, adsorbent dosage, contact time, initial solution pH, and co-existing anions. The results of adsorption displayed that the most suitable calcination temperature of FHMA is 600 °C, and the best ratio of Mg/Al is 2:1 to remove bromate anionic pollutant from water. The equilibrium adsorption data of CFHMA revealed a good compliance with the Langmuir model and the experimental data of CFHMA fitted well to the pseudo-second-order kinetic model. The calcination product of FHMA was a decent adsorbent of bromate anionic pollutant.

Keywords: Adsorption; Bromate; Calcination; Flower-like Mg-Al-layered double hydroxides.