Adsorption of Citric Acid by Synthetic Pseudoboehmite

P. Cambier and Garrison Sposito
Station de Science du Sol, Institut National de la Recherche Agronomique, Route de Saint-Cyr 78026 Versailles Cédex, France
Department of Soil Science, University of California, Berkeley, California 94720

Abstract: The adsorption of citrate, at 10−4-10−3 M initial concentration, by pseudoboehmite suspended in 0.02 M NaClO4 was investigated at varying pH. Citrate shows a strong affinity for the pseudoboehmite surface, as seen in the adsorption isotherm at pH 6. Adsorption envelopes of adsorbed citrate vs. pH for a given initial citrate concentration are characteristic for the adsorption of a polyprotic acid by a variable-charge mineral. The envelope data were fit well by the Constant Capacitance Model assuming a ligand-exchange adsorption mechanism, three monodentate surface species of citrate, and a reactive surface OH density of 0.4 mol kg−1. Aqueous speciation calculations suggest that solubility equilibrium with pseudoboehmite was attained at pH > 9 and that particulate or polymeric Al may have existed at 6 < pH < 9. Dissolved Al appeared to reduce the adsorption of citrate at pH < 5.5 via solution eomplexation reactions.

Key Words: Citrate • Pseudoboehmite • Adsorption reactions

Clays and Clay Minerals; August 1991 v. 39; no. 4; p. 369-374; DOI: 10.1346/CCMN.1991.0390405
© 1991, The Clay Minerals Society
Clay Minerals Society (www.clays.org)