XAFS Study of Cu(II) at the Water-Goethite (α-FeOOH) Interface

L. Bochatay; P. Persson; L. Lövgren; G.E. Brown Jr.

doi:doi:10.1051/jp4:1997246

Issue		J. Phys. IV France Volume 7, Number C2, Avril 1997 Proceedings of the 9th International Conference on X-Ray Absorption Fine Structure


Page(s)		C2-819 - C2-820
DOI		https://doi.org/10.1051/jp4:1997246

Proceedings of the 9th International Conference on X-Ray Absorption Fine Structure

J. Phys. IV France 7 (1997) C2-819-C2-820
DOI: 10.1051/jp4:1997246

XAFS Study of Cu(II) at the Water-Goethite (α-FeOOH) Interface

L. Bochatay¹, P. Persson¹, L. Lövgren¹ and G.E. Brown Jr.²

¹ Department of Inorganic Chemistry, Umeå University, 90187 Umeå, Sweden
² Department of Geological and Environmental Sciences, Stanford University, Stanford CA 94305-2115, U.S.A

Abstract
Cu(II) complexation at the water-goethite (α-FeOOH) interface was studied by XAFS, potentiometry, and sorption experiments. Thermodynamic data indicate that the initial Cu(II) sorption is not accompanied by release of a H⁺. As pH is raised, hydrolysis occurs, and a maximum of two H⁺ are released per sorbed ion. Sorption experiments also show that Cu(II) complexation is insensitive to variation in ionic strength, indicating inner-sphere Cu complexes. The Cu K-edge XAFS suggest that the Cu(II) surface complexes are Jahn-Teller distorted with an equatorial plane of oxygens at approximately 1.95 Å. At pH 5, no 2nd coordination shell is observed. However, at pH 8 there is a well-defined 2nd shell which is best modeled with two Cu atoms at 2.96 Å. The appearance of a 2nd coordination shell at higher pH is attributed to the formation of hydroxo-bridged Cu(II) surface polymers.