Molecular orbital calculations for modeling acetate-aluminosilicate adsorption and dissolution reactions

Possible molecular configurations of acetic acid and acetate adsorbed onto aluminosilicate minerals are examined. Molecular orbital calculations were performed on molecules and dimers that are intended to mimic inner sphere and outer sphere adsorption complexes on mineral surfaces. The results predict the structure, energetics, and vibrational spectra of the acetic acid and acetate bonded to aluminosilicate groups. The most likely surface complexes are determined by reaction energetics and comparison of theoretical to experimental vibrational spectra. In addition, a reaction pathway of Si-O-Al cleavage by acetic acid and chemisorption of acetate with tetrahedral Al3+ is predicted. An activation energy for this reaction is estimated from constrained energy minimizations of the reactants along a reaction pathway. Copyright (C) 1997 Elsevier Science Ltd.