BALANCE BETWEEN SURFACE COMPLEXATION AND SURFACE PHASE-TRANSFORMATIONAT THE ALUMINA WATER INTERFACE/

This paper synthesizes and expands on the results of a recent series o f investigations aimed at characterizing the interactions of orthophos phate, phenylphosphonate, and clodronate ions with hydrous alumina sur faces. The paper shows that gamma-Al2O3 is a thermodynamically unstabl e 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 complexati on 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 con sequences of AlPO4(s) formation are determined via a series of chemica l modeling calculations. The paper finally shows that, with respect to phenylphosphonate surface complexation, care must be taken when macro scopically derived stoichiometric compositions are used to assign micr oscopic surface complex structures.