Molecular-level investigations of effective biogenic phosphorus adsorption by a lanthanum/aluminum-hydroxide composite.

Biogenic phosphorus (P), such as organic P and inorganic pyrophosphates, could substantially contribute towards eutrophication in aquatic systems by internal loading of P from sediment through P species transformation. Previous eutrophication management studies mainly focus on the removal of orthophosphate (Ortho-P), however, an effective approach for biogenic P control from water sources, prior to incorporation in sediment, is still lacking. In this study, a lanthanum/aluminum-hydroxide (LAH) composite was demonstrated to provide both superior removal of Ortho-P and biogenic P, employing myo-inositol hexakisphosphate (IHP) and pyrophosphate (Pyro-P) as model compounds. The maximum IHP and Pyro-P adsorption capacities by LAH attained 36.4 and 21.8 mg P g-1, respectively. In order to understand the mechanisms of adsorption, zeta potential, 31P solid-state nuclear magnetic resonance (NMR) spectroscopy and P K-edge X-ray absorption near edge structure (XANES) techniques were used to characterize the LAH after adsorption. The results supported the hypothesis that the interaction between LAH and P species was through surface adsorption, by the formation of inner-sphere complexes. Linear combination fitting results of XANES data indicated that IHP and Pyro-P preferentially bonded with La-hydroxide in LAH. This study elucidates the adsorption properties and binding mechanisms of IHP and Pyro-P on lanthanum-bearing compounds at the molecular level, indicating that LAH is a promising material for the control of eutrophication.