Removal of fluoride ions from ZnSO4 electrolyte by amorphous porous Al2O3 microfiber clusters: Adsorption performance and mechanism

Amorphous porous Al2O3 microfiber clusters (AP-Al2O3-MCs) are developed by combining hydrothermal and roasting methods, which are applied to remove F- from the ZnSO4 electrolyte. Comprehensive characterization of AP-Al2O3-MCs is performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) analysis, and other techniques. The equilibrium F- removal efficiency and adsorption capacity of AP-Al2O3-MCs are 66.35% and 10.823 mg.g(-1), respectively, with an adsorbent dose of 7.0 g.L-1 at 313 K in a pH of 5 for 45 min. The isotherm study found that the Langmuir isotherm model fits the experimental data well. The theoretical maximum adsorption capacity of F- is 14.96 mg.g(-1). Adsorption kinetics can be more appropriately to described by the pseudo-second-order kinetic model. The thermodynamic data is indicative of spontaneous, exothermic, and entropy-decreasing reaction at 313 K. The defluorination mechanism is proposed, which includes the interaction of F- with Al and O on the surface of the AP-Al2O3-MCs, as well as ion-exchange by -OH groups and F-. The estimated dosage and preparation cost of the AP-Al2O3-MCs show a suitable application potential. As a result, AP-Al2O3-MCs are an ideal adsorbent for the removal of F- from the ZnSO4 electrolyte.