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Formation of Crystalline Zn-Al Layered Double Hydroxide Precipitates on γ-Alumina: The Role of Mineral Dissolution.
MedLine Citation:
PMID:  23043294     Owner:  NLM     Status:  Publisher    
Surface precipitation of metals such as nickel (Ni), zinc (Zn), and cobalt (Co) as layered double hydroxide (LDH) phases is an important pathway for toxic metal sequestration and decontamination in soil environments. To better understand their formation, here we systematically examined the presence of Al and the role of mineral dissolution during Zn sorption/precipitation on γ-Al2O3 (γ-alumina) at pH 7.5 using extended X-ray absorption fine structure spectroscopy (EXAFS), high resolution transmission electron microscopy (HRTEM), synchrotron-radiation powder X-ray diffraction (SR-XRD) and 27Al solid state NMR. Crystalline Zn-Al LDH surface precipitates were observed by HRTEM. The crystalline precipitates were flake-shaped and the crystal size is much larger than the γ-alumina substrate. This observation was corroborated by SR-XRD analysis, which showed a diffraction peak at a d-spacing of 7.58 Å. This distance is a diagnostic feature of a typical Zn-Al LDH. 27Al solid state NMR spectroscopic analysis provided the first direct evidence for the existence of Al in the precipitates while past studies have failed to conclusively demonstrate Al in the precipitate. A small shoulder at δAl-27 = + 12.5 ppm was observed and is consistent with the chemical shift of Zn-Al LDH. NMR analysis indicates that Al is transferred from the γ-alumina substrate to Zn-Al LDH precipitate. This transfer process is further supported by comparing Zn adsorption/precipitation on a series of Al (hydr)oxides with similar chemical composition but differing dissolubility. EXAFS analysis revealed that under the same experimental conditions Zn-Al LDH precipitates formed on γ-alumina and corundum but not on less soluble minerals like bayerite, boehmite, and gibbsite. These results point to substrate mineral surface dissolution as the driving force for subsequent Zn-Al co-precipitation.
Wei Li; Kenneth John Livi; Wenqian Xu; Matthew G Siebecker; Yu-Jun Wang; Brian L Phillips; Donald L Sparks
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-10-9
Journal Detail:
Title:  Environmental science & technology     Volume:  -     ISSN:  1520-5851     ISO Abbreviation:  Environ. Sci. Technol.     Publication Date:  2012 Oct 
Date Detail:
Created Date:  2012-10-9     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0213155     Medline TA:  Environ Sci Technol     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
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