Formation of Cd precipitates on γ-Al2O3: Implications for Cd sequestration in the environment. (May 2019)

• Record Type: Journal Article
• Authors: Sun, Qian; Liu, Cun; Cui, Peixin; Fan, Tingting; Zhu, Mengqiang; Alves, Marcelo Eduardo; Siebecker, Matthew G.; Sparks, Donald L.; Wu, Tongliang; Li, Wei; Zhou, Dongmei; Wang, Yujun
• Is Part Of: Environment international. Volume 126(2019)
• Page Start: 234
• Page End: 241
• Publication Date: 2019-05
• Subjects: Cadmium -- γ-Al2O3 -- Precipitation -- Cd-Al layered double hydroxide -- Cd hydroxide phases -- CdCO3; Environmental protection -- Periodicals; Environmental health -- Periodicals; Environmental monitoring -- Periodicals; Environmental Monitoring -- Periodicals; Environnement -- Protection -- Périodiques; Hygiène du milieu -- Périodiques; Environnement -- Surveillance -- Périodiques; Environmental health; Environmental monitoring; Environmental protection; Periodicals; 333.705
• DOI: 10.1016/j.envint.2019.02.036
• Languages: English
• ISSNs: 0160-4120

Abstract

Abstract: Apart from surface complexation, precipitation of minerals also plays an important role in reducing the mobility and transport of heavy metals in the environment. In this study, Cd(II) sorption species on surfaces of γ-Al2 O3 at pH 7.5 were characterized using multiple techniques. Results show that in addition to adsorption complexes, Cd hydroxide phases (Cd(OH)2 precipitates and Cdx (OH)y polynuclear complexes) were formed at the initial stages of Cd(II) sorption and gradually transformed to CdCO3 with time. In addition, Cd(II) formed CdAl layered double hydroxide (LDH) on γ-Al2 O3 under various conditions, independent of temperature and Cd loadings. The formation of Cd hydroxide phases and CdAl LDH could be ascribed to surface-induced precipitation because the bulk solution was undersaturated with respect to hydroxides. CdAl LDH formation on the Al-bearing mineral here is rather surprising because typically this occurs with elements of ionic radii similar to that of Al 3+ ; this formation is unknown for metals such as Cd(II) with a much larger ionic radius. The thermodynamic feasibility of CdAl LDH formation was further confirmed by laboratory synthesis of CdAl LDH and density function theory (DFT) calculations. These results suggest that Cd precipitation on Al-bearing minerals can be an important mechanism for Cd immobilization in the natural environment. Additionally, the finding of CdAl LDH formation on Al-bearing minerals and the thermodynamic stability of CdAl LDH provides new insights into the remediation of Cd-polluted soils and aquatic systems. Graphical abstract: Unlabelled Image Highlights: Cd hydroxide phases were generated at the initial stages of Cd(II) sorption and gradually transformed to CdCO3 . Cd(II) formed Cd-Al layered double hydroxide (LDH) on γ-Al2 O3 despite the much larger ionic radius of Cd(II) than Al(III). Cd hydroxide phases and Cd-Al LDH were formed via surface-induced process. The feasibility of Cd-Al LDH formation was verified by laboratory experiments and density function theory calculations.