In situ ATR-FTIR spectroscopic study of the co-adsorption of myo-inositol hexakisphosphate and Zn(II) on goethite

Abstract

The coexistence of myo-inositol hexakisphosphate (IHP; phytate) and aqueous Zn(II) may affect the adsorbed amounts and speciation of each other on minerals, which can further influence the transport and fate of IHP and Zn(II) in soils and sediments. The objective of this study was to investigate the co-adsorption mechanism of IHP and Zn(II) on goethite (Gt). A combination of macroscopic experiments and in situ attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) was used to investigate the co-adsorption of IHP and Zn(II) at the Gt–water interface in the pH range of 3.0–7.0. Adsorption experiments showed that the presence of IHP promoted Zn(II) adsorption, and vice versa, on the surface of Gt. The ATR-FTIR spectra of IHP adsorbed on Gt in the presence of Zn(II) differed from the spectra of IHP adsorbed without co-adsorbed Zn(II) and of zinc phytate (Zn-IHP) precipitates, suggesting that the formation of Gt–IHP–Zn ternary surface complexes was the most likely mechanism for the co-adsorption of IHP and Zn(II) on Gt. The results show that the coexistence of IHP and Zn(II) may have altered both the extent and mechanism of IHP and metal adsorption on Gt, with respect to binary Gt–IHP and Gt–Zn(II) systems. These findings indicate that the coexistence of IHP and heavy metals significantly affects the adsorbed amounts and speciation of these compounds in the natural environment, where the aqueous concentrations of reactants are below saturation with respect to metal phytate precipitates.