First principles study of water adsorption on the (100) surface of zircon:Implications for zircon dissolution

We have studied the interaction of aqueous species with the (100) face of z ircon using first-principles quantum mechanical calculations. Adsorption en ergy of molecular water on the Zr Lewis site is 1.27 eV per molecule, where as the energy of dissociative adsorption is only 0.84 eV per molecule. Thus , the non-dissociative adsorption of water is strongly preferred with respe ct to the dissociative adsorption on the (100) face of zircon. Such behavio r, which is related to the weak ability of the surface structure to relax, is changed by a 5% increase of the surface cell parameters. From our theore tical results, we propose that the exceptional resistance of zircon to diss olution may be related to the strong acidity of the Zr-O-Si bridging O atom s, which promotes the associative adsorption of water on the (100) surface of zircon.