Preparation of Mg/Al-LDH@HC composite with low concentration hydrochloric acid modified for phosphate removal from aqueous solution: Synthesis, adsorption performance and mechanism

With high microporosity, good dispersibility, excellent specific surface area and large content surface functional group, hydrochar demonstrates significant advantages and strong affinity towards pollutants in water. Modification method plays a significant role for anion adsorption by modified hydrochar, layered double hydroxide (LDH) modified hydrocarbons (Mg/Al-LDH@HC-HCl) have been synthesized through a one-step hydrothermal approach and activated with hydrochloric acid in this paper. The physical and chemical characteristics of the hydrochar, both before and after modification, are analyzed using BET, SEM-EDS, TEM, XRD, FTIR, and XPS to explore the phosphate adsorption mechanisms. The adsorption behavior of the composite follows the pseudo-second-order kinetic model and the Langmuir isotherm model, achieving a substantial adsorption capacity of 143.03 mg/g. Multiple mechanisms are leveraged within the absorption process, including pore filling, electrostatic attraction, ligand exchange, metal complexation on inner and outer surfaces, and ion exchange. An approximate 70% phosphate removal efficiency is retained by modified Mg/Al-LDH@HC-HCl after a comprehensive 5-cycle desorption using NaOH as the eluent, demonstrating the remarkable regenerability of synthesized hydrochar composite.