Effects of aluminum substitution on the surface charge of colloidal goethite particles: experiments and MUSIC modeling
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CLAY AND MODIFIED CLAYS IN REMEDIATING ENVIRONMENTAL POLLUTANTS
Effects of aluminum substitution on the surface charge of colloidal goethite particles: experiments and MUSIC modeling Shu Zhu 1 & Pei Zhang 1 & Yu Liang 1 & Mingxia Wang 1 & Juan Xiong 1 & Wenfeng Tan 1 Received: 4 November 2019 / Accepted: 21 January 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Proton adsorption behavior on the surface of Al-substituted goethites as a function of pH and ionic strength was investigated and simulated with the multisite surface complexation (MUSIC) model. In addition, X-ray diffraction, X-ray photoelectron spectroscopy, and field emission scanning electron microscope were used to characterize the crystal structure, chemical composition, micromorphology, and surface properties of the Al-substituted goethite. Al substitution was found to affect the crystal structure and micromorphology of goethite. The morphological differences did not result in significant differences in PZC value but largely affected the surface charge values. Goethite surface charge capacity increased progressively with increasing amount of Al substitution, which was attributed to increases in the density of surface coordinated sites due to the increase in (021)/ (110) face ratio. The optimization calculations enabled a satisfactory fitting of the titration data of both pure goethite and Al-substituted goethite, and the MUSIC model facilitated a more specific understanding of the charging behavior of Alsubstituted goethite. The singly (≡FeOH−0.5 + ≡AlOH−0.5) and triply coordinated (≡Fe3O−0.5 + ≡AlFe2O−0.5) surface groups were most likely responsible for the basic charging behavior of goethite in the pH range of 4–10. All results indicate that the MUSIC model has excellent performance in characterizing Al-substituted goethite, and the model has promising application prospect in other substituted metal (hydr)oxides. Keywords Iron oxides . Al-substituted goethite . Micromorphology . Acid-base titrations . Proton adsorption . MUSIC model
Introduction Goethite (α-FeOOH) is a ubiquitous and one of the most important iron minerals in soils and sediments (Schwertmann and Cornell 2008). It plays important roles in environmental processes due to its strong affinity with different contaminants (Schwertmann and Cornell 2008; Zhang et al. 2017). The reactivity of mineral particles is directly associated with their surface structure and composition (Venema et al. 1998). A crystallography-based approach can be used to assess the composition and structure of the surface. Shu Zhu and Pei Zhang contributed equally to this work. Responsible Editor: Philippe Garrigues * Mingxia Wang [email protected] 1
Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtze River), Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, People’s Republic of China
The crystal structure of goethite relies on the coordination of Fe3+ with OH− and O2− in specific geometries.
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