Adsorption, desorption, and surface-promoted hydrolysis of glucose-1-phosphate in aqueous goethite (alpha-feooh) suspensions
J. S. Loring
Summary, in English
Adsorption, desorption, and precipitation reactions at environmental interfaces govern the fate of phosphorus in terrestrial and aquatic environments. Typically, a substantial part of the total pool of phosphorus consists of organophosphate, and in this study we have focused on the interactions between glucose-I-phosphate (G I P) and goethite (alpha-FeOOH) particles. The adsorption and surface-promoted hydrolysis reactions have been studied at room temperature as a function of pH, time, and total concentration of GIP by means of quantitative batch experiments in combination with infrared spectroscopy. A novel simultaneous infrared and potentiometric titration (SI PT) technique has also been used to study the rates and mechanisms of desorption of the surface complexes. The results have shown that GIP adsorption occurs over a wide pH interval and at pH values above the isoelectric point of goethite (IEPgoethite = 9.4), indicating a comparatively strong interaction with the particle surfaces. As evidenced by IR spectroscopy, GIP formed pH-dependent surface complexes on goethite, and investigations of both adsorption and desorption processes were consistent with a model including three types of surface complexes. These complexes interact monodentately with surface Fe but differ in hydrogen bonding interactions via the auxiliary oxygens of the phosphate group. The apparent desorption rates were shown to be influenced by reaction pathways that include interconversion of surface species, which highlights the difficulty in determining the intrinsic desorption rates of individual surface complexes. Desorption results have also indicated that the molecular structures of surface complexes and the surface charge are two important determinants of GIP desorption rates. Finally, this study has shown that surface-promoted hydrolysis of GIP by goethite is base-catalyzed but that the extent of hydrolysis was small.