Surface adsorption and precipitation of inositol hexakisphosphate on calcite: A comparison with orthophosphate

- A similar P amount was sorbed on calcite for OP and IP through surface P precipitation.
- A sphere-shaped amorphous calcium phytate was formed when calcite reacted with IHP.
- A plate-shaped crystalline hydroxylapatite was formed when calcite reacted with Pi.
- The formation of hydroxylapatite may base on dissolution-precipitation mechanism.
- Calcium phytate can form via the dissolution-complexation-precipitation processes.

Unraveling the processes of adsorption-precipitation of organic phosphates (OPs) on calcite is important for understanding the transformation, mobility and bioavailability of phosphorus (P) in calcareous soils. To elucidate these processes, the interaction between myo-inositol hexakisphosphate (IHP) and calcite was studied using macroscopic sorption experiments and a variety of analytical approaches. The experiments were also conducted with orthophosphate (Pi) for comparison. Calcite presented a similar sorption capability for IHP and Pi through the rapid formation of surface precipitates based on sorption experiments and the results of Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and solid-state 31P nuclear magnetic resonance (NMR) spectroscopy. After interacting with IHP/Pi, two different types of precipitates on a calcite surface could be directly observed by SEM images and analyzed by energy dispersive spectroscopy (EDS): a sphere-shaped precipitate considered typical for the poorly crystallized calcium phytate and a plate-shaped precipitate considered typical for the crystalline hydroxylapatite. This study suggests that active calcite strongly influences the species and behavior of IHP via a rapid surface precipitation reaction in a natural environment and advances our knowledge for predicting the fate of dissolved OP species in a variety of calcareous soils and geological settings enriched with calcite.

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