Effects of particle size and biofilm pre-coating on phosphorus adsorption and capping performance by ZnAlLa-NO<sub>3</sub>-LDHs@quartz sand for internal phosphorus control in three lake sediments.

Abstract

This study systematically evaluates phosphorus (P) adsorption and capping performance of core-shell ZnAlLa-NO₃-layered double hydroxides (LDHs)@quartz sand (QS) materials, focusing on the influence of particle size and biofilm pre-coating in their practical application for lake management. In 24 h adsorption experiments (adsorbent dosage: 1.0 g/L), 200 mesh LDHs@QS (QSL) exhibited a significantly higher P adsorption capacity (Q_m, 9.58 mg/g) than 20 mesh QSL (2.31 mg/g), as derived from the Langmuir model. Fourier transform infrared spectra (FTIR) and X-ray photoelectron spectroscopy (XPS) confirmed that phosphate adsorption by LDHs involved inner-sphere complexation, ion exchange, and chemical adsorption. In a 14 d capping experiment, P release reduction was primarily determined by material type rather than particle size or initial sediment P levels. Specifically, LDH-based materials, with or without biofilm (QSLB: 88.3% and QSL: 91.3%), significantly outperformed the original QS (70.4%). Total P flux even reversed to negative values, particularly in the QSLB treatments, which exhibited the lowest proportion of loosely bound P (1.8%), compared to 3.5% for QSL and 13.1% for QS. Principal component analysis revealed that QSLB had minimal disturbance to overlying water and sediment properties relative to the blank control, highlighting its environmental compatibility. Moreover, nitrate-intercalated LDHs functioned as a slow-release oxidant, enhancing the oxidation-reduction potential (ORP) of overlying water, demonstrating their multifunctional potential for long-term internal P control. This study lays a groundwork for customizing core-shell LDH-based capping materials for efficient and environmentally friendly remediation of eutrophic water bodies.