Chemisorption of Copper on Hydroxy-Aluminum-Hectorite: An Electron Spin Resonance Study

J. B. Harsh1, H. E. Doner1 and M. B. McBride2
1 Department of Plant and Soil Biology, University of California, Berkeley, California 94720
2 Department of Agronomy, Cornell University, Ithaca, New York 14853

Abstract: Copper adsorption on a hydroxy-aluminum-hectorite complex (OH-Al-hectorite) at pH 4.5, 5.7, 7.4, and 7.8 was examined by means of electron spin resonance. The spectra of these samples were compared to those of Cu2+-hectorite and various aluminum hydrous oxides. Copper on the OH-Al-hectorite in aqueous gels occurred as mobile Cu(H2O)62+ and chemisorbed to discrete sites of the OH-Al interlayer. As pH was increased, the ratio of chemisorbed to mobile Cu2+ increased. At pHs above 7 the solubility product of Cu(OH)2 was exceeded, but chemisorbed Cu2+ remained as the dominant species. These results contrast with the precipitation of Cu observed on microcrystalline gibbsite above pH 5 and indicate that the interlayer OH-Al retained more Cu2+ on discrete sites. The greater adsorption capacity probably resulted in part from a higher specific surface area. Electron spin resonance spectra of Cu2+ in air-dried films of the OH-Al-hectorite at pH 4.5 and 7.4 showed Cu2+ in square planar symmetry, oriented with the z-axis perpendicular to the OH-Al-hectorite a–b plane. At the higher pH, the spectrum resembled that of Cu(OH)42− on alumina, suggesting a ligand exchange mechanism for Cu2+ adsorption on the complex.

Key Words: Adsorption • Aluminum • Copper • Electron spin resonance • Hectorite • Hydroxy-aluminum complex

Clays and Clay Minerals; October 1984 v. 32; no. 5; p. 407-413; DOI: 10.1346/CCMN.1984.0320509
© 1984, The Clay Minerals Society
Clay Minerals Society (www.clays.org)