Pilot-scale valorization of hazardous aluminum dross into γ-Al2O3 nanoadsorbent for efficient removal of fluoride

Abstract

Abstract In this study, secondary aluminum dross as an alumina-rich resource was valorized into the gamma-aluminum oxide ( γ -Al2O3) via a pilot-scale extraction system. The pilot-scale process was designed for a total\u2009 γ -Al2O3 production of\u2009 ∼ 5 kg/day. The extraction process included leaching, precipitation, hydroxide separation, aluminum hydroxide re-precipitation, drying and high-temperature dihydroxylation The obtained\u2009 γ -Al2O3 was then characterized using XRD, XRF, BET, and FESEM. The XRD analysis disclosed the emergence of the gamma-crystalline phase with a crystallite size of 19.6nm. The XRF revealed a purity of more than 99 wt%. The BET surface area, pore volume, and mean pore size were\u2009 ∼ 170 m2/g, 0.45cm 3/g, and 17.4nm, respectively. The FESEM and TEM indicated that the as-synthesized\u2009 γ -Al2O3 was in the form of agglomerates, consisting of γ -Al2O3 was then used to adsorb aqueous fluoride with two different concentrations of 10 and 20 ppm. The adsorption results revealed that the amount of fluoride adsorbed by\u2009 γ -Al2O3 was 16.5 mg/g when adsorbent dosage, initial fluoride concentration, pH, and equilibrium time were 1 g/l, 20 ppm, 4, and 1 h, respectively. The maximum monolayer adsorption was obtained 35.6 mg/g by Langmuir model. Investigating the influence of the adsorbent dosage indicated that the adsorbent dosage of 4 g/l resulted in 98% fluoride removal. It was found that fluoride adsorption occurred through chemisorption, and carbonate and phosphate anions had the most interference with fluoride adsorption. The regeneration experiments showed that the regenerated\u2009 γ -Al2O3 can exhibit good fluoride adsorption performance, even after 8 times regeneration.