RETRACTED ARTICLE: Kinetic, isotherm, thermodynamic and mechanism investigations of dihydrogen phosphate removal by MgAl-LDH

Abstract

In this study, Mg–Al layered double hydroxide (MgAl-LDH) was synthesized by the urea hydrolysis method and used as sorbent to remove phosphate from aqueous solutions. Structural and morphological studies show that MgAl-LDH was prepared successfully with good crystallinity. The influences of sorbent dosage, time, initial concentrations, solution pH, temperature and competitive ions on the phosphate uptake have been investigated. It has been found that the uptake of phosphate onto MgAl-LDH was rapid and reached equilibrium within 60 min. The kinetic data were studied in terms of the pseudo-first-order, pseudo-second-order, elovich and intraparticle diffusion kinetic models. The pseudo-second-order model best described the sorption process. The isothermal data are best fitted by Freundlich, suggesting that multiple processes may control the adsorption of phosphate on the MgAl-LDH. The maximum adsorption capacity at 25 °C was found to be 346.4 mg/g. The sorption mechanism of phosphate onto LDHs could be via electrostatic attraction, ligand exchange and ion exchange. Phosphates ion uptake in the presence of other ions decreases in the order NO3− > Cl− > SO42−. Thermodynamic experiments suggested that the phosphate adsorption was spontaneous (− ΔG°) and endothermic (+ ΔH°) and increased the randomness (+ ΔS°) in the system. Thus, MgAl-LDH prepared by urea hydrolysis method is an effective sorbent for the removal of phosphate from aqueous solutions.