[Adsorption Behavior of Phosphate from Water on Zirconium-loaded Granular Zeolite-amended Sediment]

In this study, a zirconium-loaded granular zeolite (ZrGZ) was prepared, characterized and used as a sediment amendment to control internal phosphorus (P) loading in water samples from a heavily polluted river. The adsorption characteristics of phosphate on ZrGZ-amended sediment were investigated using batch experiments, and the stability of P in phosphate-adsorbed ZrGZ was evaluated using a sequential chemical extraction method. Results showed that the Langmuir isotherm model was more suitable for describing the equilibrium adsorption data of phosphate on ZrGZ-amended sediment than the Freundlich and Dubinin-Radushkevich isotherm models. The adsorption process of phosphate on ZrGZ-amended sediment could be well described by the pseudo-second-order and Elovich kinetic models, and both film and intra-particle diffusion controlled the adsorption rate during the gradual adsorption stage. The coexistence of SO₄^2- and HCO₃^- inhibited the adsorption of phosphate on ZrGZ-amended sediment, while coexisting Na⁺, K⁺, Mg²⁺ and Ca²⁺ enhanced the phosphate adsorption, and this promoting effect decreased in the order of Ca²⁺ > Mg²⁺ > Na⁺/K⁺. The ZrGZ-amended sediment exhibited a higher phosphate adsorption capacity than the unamended sediment, and the maximum phosphate adsorption capacity derived from the Langmuir isotherm model was found to be 336 mg·kg^-1, which was higher than that for the unamended sediment (215 mg·kg^-1). Sequential tests showed that P in phosphate-adsorbed ZrGZ mainly existed in the form of NaOH-rP and Res-P, which was relatively unreactive. These results indicated that ZrGZ addition enhanced the phosphate adsorption capacity of river sediment, and that ZrGZ was a promising amendment for controlling the release of P from river sediment.