Balance between surface complexation and surface phase transformation at the alumina/water interface

Summary, in English

This paper synthesizes and expands on the results of a recent series of investigations aimed at characterizing the interactions of orthophosphate, phenylphosphonate, and clodronate ions with hydrous alumina surfaces. The paper shows that gamma-Al2O3 is a thermodynamically unstable substance in water, which undergoes a (surface) phase transformation into bayerite, beta-Al(OH)(3). Furthermore, it also shows that while phenylphosphonate ions are exclusively adsorbed via surface complexation to the alumina surfaces, clodronate ions dissolve the alumina phase and precipitate as an aluminum clodronate phase. Orthophosphate ions show a transient behavior in this respect, and the limits for, and consequences of AlPO4(s) formation are determined via a series of chemical modeling calculations. The paper finally shows that, with respect to phenylphosphonate surface complexation, care must be taken when macroscopically derived stoichiometric compositions are used to assign microscopic surface complex structures.