Quantitative and spectroscopic investigations of the co‐sorption of myo‐inositol hexakisphosphate and cadmium(II) on to haematite

Abstract

SummaryThe interactions between phosphates, both inorganic and organic ones, and heavy metals on mineral surfaces affect their environmental fate and transport. In this research, we investigated the co‐sorption of myo‐inositol hexakisphosphate (IHP) and cadmium (Cd(II)) on to haematite at various pHs in batch experiments, zeta (ζ) potential measurement and in situ attenuated total reflectance Fourier transform infrared (ATR‐FTIR) spectroscopy. In the haematite–IHP binary system, IHP formed inner‐sphere complexes on haematite in which some phosphate groups of the IHP molecule bonded with the haematite surface, and other dissociated phosphate groups were ionized. In the haematite–IHP–Cd ternary system, the presence of aqueous Cd(II) increases IHP sorption and the ζ potential of haematite relative to that in the haematite–IHP binary system. The enhancement is more obvious at higher pHs, reversing the initial pH dependence of IHP sorption in the binary system. Similarly, the coexisting IHP promotes the retention of Cd(II) on haematite. The ATR‐FTIR spectroscopy indicates the formation of two structurally distinct ternary surface complexes (the Hm–IHP–Cd surface complex and the Hm–Cd–IHP–Cd surface complex). Our results suggest that simultaneous sorption not only increases the sorption density of IHP and Cd(II), but also changes the surface complex configuration of IHP and Cd(II) on haematite.Highlights The interactions between IHP and Cd(II) on haematite were investigated. The presence of Cd(II) increases IHP sorption and vice versa. IHP and Cd(II) co‐sorption is enhanced as pH increases. Two structurally distinct ternary surface complexes form on haematite surfaces.