Adsorption and precipitation of myo‐inositol hexakisphosphate onto kaolinite

Abstract

Sorption of myo‐inositol hexakisphosphate (IHP), a common type of organic phosphorus in soils, largely controls its mobility and bioavailability. Research on the interaction between IHP and phyllosilicate minerals such as kaolinite, which is commonly present in highly weathered soils, has often been neglected, probably due to the common assumption that negatively charged phyllosilicate minerals have low sorption capacity and binding affinity to IHP and thus do not play any significant role in its fate. Here, the interaction between IHP and poorly crystallized kaolinite (KGa‐2) was investigated in batch experiments using Zeta (ζ) potential measurement and 31P nuclear magnetic resonance (NMR) spectroscopy. The results showed that dissolved Al(III) concentration at the adsorption initiation stage increased with increasing IHP concentration at pH 4.0. From pH 2.5 to 9.0, IHP presented a maximum sorption capacity (50 μmol g−1) at pH 4.0 at 24 hr. With IHP sorption, the ζ potential of kaolinite first decreased sharply to a negative value, then gradually increased with resorption of Al(III) released from kaolinite dissolution at acidic pH, and finally approached the original value of the pure kaolinite. 31P NMR spectroscopy and ζ potential analyses revealed that IHP formed inner‐sphere surface complexes and aluminium phytate precipitated on kaolinite at low pH (2.5 and 4.0), whereas the formation of inner‐sphere surface complexes was the dominant sorption mechanism at pH ≥ 5.5. This study implies that various mechanisms, depending on ambient pH condition, can dominate the IHP sorption onto kaolinite, which impacts the mobility and bioavailability of phosphorus in highly weathered soils. Highlights IHP promotes the dissolution of kaolinite mainly through the formation of aluminium phytate complex. IHP sorption presents a sharp maximum at pH 4.0. IHP forms inner‐sphere complexes at the surface of kaolinite. Formation of aluminium phytate surface precipitates is favourable at relatively low pH.

Solution 31P NMR Investigation of Inositol Hexakisphosphate Surface Complexes at the Amorphous Aluminum Oxyhydroxide–Water Interface

“…Yan et al further suggested that the Al–PO 4 complexes then transformed to surface precipitates with time. A surface precipitation mechanism was also suggested in kaolinite at pH 4 using solid-state NMR . Del Nero et al and Li et al studied phosphate adsorption kinetics on corundum (α-Al 2 O 3 ).…”

“…A surface precipitation mechanism was also suggested in kaolinite at pH 4 using solid-state NMR. 31 Del Nero et al 30 and Li et al 29 studied phosphate adsorption kinetics on corundum (α-Al 2 O 3 ). The formation of bidentate binuclear inner-sphere complexes was reported, 29 along with precipitation at high P surface coverage.…”

“…The formation of bidentate binuclear inner-sphere complexes was reported, 29 along with precipitation at high P surface coverage. 30 An alternative way is ex situ 31 P MAS NMR, which also provided valuable insights on this P adsorption process. Numerous researchers studied P adsorption on Al (oxyhydr)oxides by 31 P MAS NMR.…”

Unravelling the Role of Rhizosphere Microbiome and Root Traits in Organic Phosphorus Mobilization for Sustainable Phosphorus Fertilization. A Review

“…In addition to Pi, soil Po are an important P pool [42], especially in soils treated with organic inputs [43]. Studies which quantify Po in organic inputs and soils report different values for the amount of Po in soils, ranging from 20 to 90% of the total P pool in soils and sediments [44][45][46][47][48]. A random-effects meta-analysis performed by Darch et al [49], based on different studies, showed that the contribution of Pi and Po to total P varied significantly in organic input or soil (Tables 1-4): for organic input, the contribution of Pi was found to be 5200 mg•kg −1 compared to nearly 4000 mg•kg −1 for the Po pools.…”

“…In soils, P forms and amounts vary with soil type [55], land use, and fertilizer history [56]. Given these large pools of Po in soil and fertilizer and the range of values (20-90% of total P) generally contained in soils and sediments [45,48], it is critical to consider Po dynamics along with Pi in order to improve P cycles in agroecosystems. Current understanding suggests that Po is as significant in amount as Pi.…”