Sorption of Cu(II) onto vineyard soils: macroscopic and spectroscopic investigations
Résumé
The sorption of Cu on five vineyard soils was examined via macroscopic and spectroscopic investigations. The composition of the soils was previously determined using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). X-ray absorption spectroscopy (XAS) was employed to determine the metal environment with regard to the identity and interaction of the nearest atomic neighbors, the bond distances, and the coordination numbers. The five soils present similar sorption properties and there is no XAS evidence that the nature of the soil samples affects the local chemical environment of Cu(II). The kinetics of the Cu sorption reactions is rapid, with the equilibrium loading of Cu on the surface achieving approximately 200 μmol g−1, i.e., 12.7 mg g−1. The XAS data indicate that Cu is adsorbed in the form of inner-sphere complexes with first shell Cu–O parameters of four equatorial Cu–O bonds equal to 1.93 Å and two axial Cu–O bonds at 2.43 Å. This is in accordance with a Jahn–Teller distorted octahedron environment around copper. Our results provide evidence of the complexation of Cu(II) onto soil organic matter coated with an inorganic surface (quartz, clay, and goethite).