Use of calcined layered double hydroxide [Zn$_{2}$-Al-CO$_{3}$] for removal of textile dye acid green 1 from wastewater: kinetic, equilibrium, comparative, and recycling studies

摘要

In the present study, calcined layered double hydroxides (CLDHs) were obtained by heating [Zn$_{2}$-Al-CO$_{3}$] at 500 $^{circ}$C. The adsorption of the textile dye acid green 1 (AG1) by CLDH was carried out at different pH levels, adsorbent--adsorbate contact times, and AG1/CLDH mass ratios. Equilibrium at room temperature was reached after 24 h, which was confirmed by the kinetic modeling of the experimental data by the pseudo-second-order model. The adsorption is described by a Langmuir-type isotherm. The comparative study of adsorption isotherms in calcined and uncalcined phases reveals that the former could be a good candidate for trapping such pollutants. After removal of AG1, characterization of the CLDH solids by X-ray diffraction and infrared spectroscopy showed that the adsorption is also enhanced by reconstruction of a hydrotalcite matrix intercalated by AG1. The removal of AG1 by CLDH gave satisfactory results. Under optimum conditions, the retention is total when mass ratio AG1/CLDH is between 0.58 and 0.75. The material can be recycled by a series of anion exchange reactions and its retention capacity reaches 833.33 mg/g. This retention capacity was only reduced by 10% after the fifth recycling cycle.