Removal of F- from industrial ZnSO4 solution by hierarchical porous Al2O3-ZnO microspheres: performance and mechanism

As mineral resources are developed and exploited, the proportion of low-grade zinc ore increases. The concentrations of F - exceeding the optimal range may pose a risk to zinc hydrometallurgy . In the present research, Al 2 O 3 -ZnO microspheres (AZO) characterized by a substantial specific surface area were synthesized through a hydrothermal-roasting technique and applied in industrial zinc sulphate fluoride removal. The optimal adsorption conditions for AZO and the underlying adsorption mechanism were investigated. The results indicated that the adsorption at 12 g·L -1 dosage, original pH=5.32 of the solution and 323 K for 75 min, when the fluoride concentration was reduced to below 50 mg·L -1 , the fluoride removal percentage reached 73.32 %, and the adsorption capacity was 8.55 mg·g -1 . Kinetic studies revealed that AZO exhibited surface inhomogeneity, functioning as a heterogeneous adsorbent, with the fluoride adsorption process being predominantly chemical in nature. The isotherm model suggested that the removal process was characterized by homogeneous adsorption of a monomolecular layer, with a theoretical maximum adsorption capacity of AZO estimated at 9.479 mg·g -1 . FT-IR and XPS analyses demonstrated that the defluorination process occurs through ion exchange between F - and -OH, as well as the formation of Zn/Al-F complexes. Consequently, AZO present a novel approach for developing an effective adsorbent for defluorination in industrial ZnSO 4 solutions.