The role of fluoroaluminate complexes on the adsorption of fluoride onto hydrous alumina in aqueous solutions

JOURNAL OF COLLOID AND INTERFACE SCIENCE

卷:561

Article

Lin, Jui-Yen¹  Chen, Yung-Long²  Hong, Xin-Ya²  Huang, Chinpin²  Huang, C. P.³ 

[1] Natl Cheng Kung Univ, Dept Chem Engn, Tainan 701, Taiwan

[2] Natl Chiao Tung Univ, Inst Environm Engn, Hsinchu 300, Taiwan

[3] Univ Delaware, Dept Civil & Environm Engn, Newark, DE 19716 USA

关键词: Fluoride;    gamma-Al2O3;    Fluoroaluminate complexes;    Adsorption;    Surface complexation;    Surface acidity;   

DOI  :  10.1016/j.jcis.2019.10.085

来源: Elsevier

【 摘 要 】

Activated alumina (AA) has been extensively applied in the defluorination of industrial wastewaters and groundwater. Although the dissolution of AA due to formation of fluoroaluminate complexes (AlFx3-x), especially in acidic condition, has been observed, its role on fluoride uptake by alumina has not been discussed in any previous literature, most of which consider F- as the sole adsorbed species. The present study described the effect of fluoroaluminate complexes on fluoride adsorption onto alumina. Results indicated that fluoroaluminate complexes, major fluoride species at pH < 6, were responsible for total fluoride adsorbed. Free fluoride ions were adsorbed mainly in the alkaline pH region, e.g., pH > 6. The dissolution of AA during defluorination was measured and analyzed by the thermodynamic solubility model. The surface concentration of F- and AlFx3-x were calculated considering electrostatic interactions. Characterization of fluoride-laden AA by XPS revealed that the fraction of surface Al-F species decreased with pH, which suggested the transition of the surface fluorinated species to that of free fluoride ions. The stability constants of four surface complexes, namely, AIOH-FAl2+, AlOH-F2Al+, AlOH2(+)(F)-F-, and AIOH-F-, were 10(6.88), 10(5.36), 10(2.72) and 10(2.36), respectively. Obviously fluoroaluminate complexes exhibited stronger chemical bonds with the surface hydroxy species than free fluoride. (C) 2019 Published by Elsevier Inc.

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