The chemical behaviors of polyphosphate at mineral-water interfaces is of fundamental importance in controlling the phosphorus (P) sequestration and bioavailability in aqueous environments. In this study, we investigated the kinetics and mechanisms of polyphosphate sorption and hydrolysis onto three different size γ-Al2O3 phases in the absence or presence of different divalent metal cations (Ca2+, Cu2+, Mg2+, Mn2+, Zn2+) at pH 6 and 8. All metal cations showed some degree of enhancement of polyphosphate hydrolysis. Particularly, the presence of Ca2+ significantly enhanced the hydrolysis rate of polyphosphate by g-Al2O3, with almost 4-fold increase at pH 6 and 9-fold increase at pH 8. The hydrolysis rate was dependent on the size of the γ-Al2O3 particle size, with an order of 5 nm &gt; 35 nm &gt; 70 nm λ-Al2O3, regardless of Ca2+ presence and pH values, due to the higher surface area of smaller size mineral particles. Solid-state 31P SP/MAS nuclear magnetic resonance (NMR) spectroscopy analyses revealed that the mainly surface P species included calcium phosphate precipitate, phosphate group as bidentate surface complexes, and phosphate group in polyphosphate not associated with the mineral surface. 2D 31P{1H} CP-HetCor analyses further determined the amorphous nature of the formed calcium phosphate precipitates. Our results revealed the critical role of mineral-water interface interactions and divalent metal cation in the degradation and transformation of polyphosphate and will lay the foundation for better understanding of the interfacial geochemical processes governing polyphosphate fate and phosphorus cycling in natural environments.

Size-dependent adsorption and hydrolysis of polyphosphates on aluminum oxides

2019 Spring National Meeting

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