Performance and mechanism of hierarchical porous Al2O3-MgO nanosheets for removing fluoride ions from industrial ZnSO4 solution

Excessive concentration of fluoride ion (F-) in ZnSO4 solution will cause serious harm to zinc electrowinning. Therefore, it is necessary to defluorinate the ZnSO4 solution to reduce the concentration of F- to below 50 mg·L-1 to ensure the smooth progress of subsequent production. In this study, Al2O3-MgO nanosheets (HP-AMO-NTs) with typical hierarchical porous structure were prepared by hydrothermal-roasting method. The synthesized HP-AMO-NTs were characterized by XRD, SEM-EDS, BET, FT-IR and XPS. In order to evaluate the performance of HP-AMO-NTs for F- removal, we studied various factors affecting F- adsorption. When the F- concentration decreased to a reasonable range (<50 mg·L-1), the optimal removal percentage and adsorption capacity were 65.80% and 9.13 mg·g−1, respectively. The correlation coefficient of Pseudo-second-order kinetic model and Langmuir adsorption isotherm model was the highest. According to thermodynamic analysis, the adsorption and defluoridation of HP-AMO-NTs was a spontaneous, exothermic and entropy-reducing reaction. SEM-EDS analysis showed that a large amount of fluorine entered into HP-AMO-NTs after adsorption. FT-IR and XPS analysis showed that F- was ion-exchanged with hydroxyl (–OH) adsorption active groups and coordinated to form Mg/Al-F complexes to achieve removal from ZnSO4 solution. The theoretical maximum adsorption capacity of HP-AMO-NTs is 10.73 mg·g−1, indicating that HP-AMO-NTs is a potential efficient adsorbent for removing F- from industrial ZnSO4 solution. This provides a new idea for the development of high-performance ZnSO4 solution defluorination materials.