Surface Complexation of Calcite by Carboxylates in Water

✍ Scribed by C. Geffroy; A. Foissy; J. Persello; B. Cabane

• Publisher: Elsevier Science
• Year: 1999
• Tongue: English
• Weight: 120 KB
• Volume: 211
• Category: Article
• ISSN: 0021-9797
• DOI: 10.1006/jcis.1998.5966

✦ Synopsis

Small molecules that have two carboxylic functions can adsorb from water onto calcite. The adsorption site is a ؊Ca ؉ site. The mechanism of adsorption is a complexation of the ؊Ca ؉ site by the two carboxylates, similar to the solution complexation of Ca ؉؉ ions. The complex has a ring structure where the two carboxylates are joined on one side by the ؊Ca ؉ ion and on the other by the n CH 2 groups of the small molecule. Five-bond rings (n ‫؍‬ 0) are the most stable, followed by six-bond rings (n ‫؍‬ 1) and seven-bond rings (n ‫؍‬ 2). Five-bond rings can also be formed with one carboxylate and one hydroxyl group (this is the case for ␣-hydroxycarboxylates) or with one enolate and one hydroxyl group (catechol). The sequence of binding strengths is enolate > carboxylate > hydroxyl; it matches the sequence of complexation efficiencies of these groups in solution and their characters as electron donors toward the metal cation.