Interaction of inositol phosphate with calcite

The interaction of myo-inositol hexaphosphate with calcite was studied to evaluate the adsorption mechanisms and the electrochemical modifications induced by interaction of a molecule at such a high-charge density. In addition to quantitative information through the construction of adsorption isotherms, FT-IR and Laser Doppler Velocimetry - Photon Correlation Spectroscopy (LDV-PCS) were employed to investigate the nature of the adsorbent-adsorbate bonds and to determine the electrophoretic mobility and size of the particles before and after sorption. The experiments were also run with orthophosphate (Pi) for comparison. The amount of sorbed P increased to reach a plateau at 17.8 mu mol m(-2) for inositol hexaphosphate (IHP) while for Pi rose 1.4 mu mol m(-2) but at C-e > 6.10(-4) M it had a sharp increase reaching 155 mu mol m(-)2. As expected, for Pi, adsorption predominated up Ce 6.10(-4)M by covering about 20% of total surface. The adsorption occurred at sites that behaved as nucleus of formation of the clustering of Ca- and PO4-ions with the ending formation of calcium phosphate precipitates at C-e higher than 6.10(-4)M. The reaction of inositol hexaphosphate with calcite involves, besides adsorption, precipitation of Ca salts and hence calcite dissolution also at the lowest added IHP concentrations, accounting for the large amount retained by calcite. Sorption of IHP on calcite caused aggregation of particles at low concentrations followed by an increase of their negative charge and hence re-dispersion at higher concentrations. These results indicate a great IHP-fixing capacity of calcite that can affect its accumulation in soils and P bioavailability, and a considerable change of calcite electrochemical properties and particle size distribution that can modify aggregate stability.