Copper Sorption Mechanisms on Smectites
- Univ. of Idaho, Moscow, ID (United States)
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Abstract– Due to the importance of clay minerals in metal sorption many studies have attempted to derive mechanistic models that describe adsorption processes. These models often include several different types of adsorption sites, including permanent charge sites and silanol and aluminol functional groups on the edges of clay minerals. The edge sites have similar pH-dependent adsorption properties as many oxide minerals. To provide a basis for development of adsorption models it is critical that molecular level studies be done to characterize sorption processes. In this study we conducted XAFS and ESR spectroscopic experiments on copper (II) sorbed on smectite clays using suspension pH and ionic strength as variables. At low ionic strength, results suggest that Cu is sorbing in the interlayers and maintains its hydration sphere. At high ionic strength Cu atoms are excluded from the interlayer and sorb primarily on the silanol and aluminol functional groups of the montmorillonite or beidellite structures. Interpretation of the XAFS and ESR spectroscopy results provides evidence that multinuclear complexes are forming on the edge sites. Fitting of EXAFS spectra revealed that the Cu-Cu atoms in the multinuclear complexes are 2.65 Å apart, and have coordination numbers near one. This structural information suggests that small Cu dimers are sorbing on the surface. These complexes are consistent with observed sorption on mica and amorphous silicon dioxide, as well as the Cu-bearing silicate minerals plancheite and shattuckite, yet are inconsistent with previous spectroscopic results for Cu sorption on montmorillonite. We hypothesize that the differences in sorption mechanisms on the edges of the montmorillonite are due to loading level. The results reported in this paper provide mechanistic data that will be valuable for modeling surface interactions of Cu with clay minerals, and predicting the geochemical cycling of Cu in the environment.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 15010591
- Report Number(s):
- PNNL-SA-39924; 2206; KP1301030
- Journal Information:
- Clays and Clay Minerals, Vol. 52, Issue 3; ISSN 1552-8367
- Country of Publication:
- United States
- Language:
- English
Similar Records
Prediction of metal sorption in soils
Cs, Sr, and Ba Sorption on Clays and Fe-Oxides