Adsorption of fluoride on clay minerals and their mechanisms using X-ray photoelectron spectroscopy |
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Authors: | Junyi Du Daishe Wu Huayun Xiao Ping Li |
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Institution: | 1. Department of Environmental Science and Engineering, Nanchang University, Nanchang, 330031, China
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Abstract: | This research investigates the adsorption mechanisms of fluoride (F) on four clay minerals (kaolinite, montmorillonite, chlorite, and illite) under different F? concentrations and reaction times by probing their fluoride superficial layer binding energies and element compositions using X-ray photoelectron spectroscopy (XPS). At high F? concentrations (C 0 = 5?C1000 mg·L?1), the amount of F? adsorbed (Q F), amount of hydroxide released by clay minerals, solution F? concentration, and the pH increase with increasing C 0. The increases are remarkable at C 0>50 mg·L?1. The QF increases significantly by continuously modifying the pH level. At C 0<5?C100 mg·L?1, clay minerals adsorb H+ to protonate aluminum-bound surface-active hydroxyl sites in the superficial layers and induce F? binding. As the C 0 increases, F?, along with other cations, is adsorbed to form a quasi-cryolite structure. At C 0>100 mg·L?1, new minerals precipitate and the product depends on the critical Al3+ concentration. At Al3+]>10?11.94 mol·L?1, cryolite forms, while at Al3+]<10?11.94 mol·L?1, AlF3 is formed. At low C 0 (0.3?C1.5 mg·L?1), proton transfer occurs, and the F? adsorption capabilities of the clay minerals increase with time. |
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