Synthesis of LDH/Alginate composite beads as a potential adsorbent for phosphate removal: kinetic and equilibrium studies

Recently, layered double hydroxides (LDH) have attracted a lot of interest due to their characteristics and biocompatibility for various applications. Although they have advantages, LDHs often have several limitations regarding application requirements, such as aggregation due to their high surface properties and are difficult to recover from aqueous solutions. In addressing these issues, the recent developments in the fabrication of intelligent LDHs composites based on biopolymer. The objective of this study was to investigate the phosphate removal. Using successfully synthesized double layered hydroxide (LDH) and alginate composite beads. The sample was characterized by X-ray diffraction and Scanning Electron Microscopy coupled with Energy Dispersive X-ray (SEM–EDX). SEM images confirm the successful incorporation of sodium alginate into LDH. They indicate that the surface of the LDH/alginate beads has a heterogeneous topography and that the LDH powder has been mixed with the alginate polymers. The efficiency and percentage removal were examined along with various influencing factors like adsorbent dose, solution pH, kinetic time, initial phosphate concentration, temperature and salt concentration also carried out (adsorbent dose = 0.02 g in 40 ml solution; initial phosphate concentration = 100 mgP/l; reaction time = 2 h). The results proved that the composites were effective in removing phosphate with a sorption capacity of 73% under the given experimental conditions. The phosphate removal was not sensitive to initial solution pHs between 2 and 12 and was not affected by the presence of salt. The adsorption process follows the Langmuir isotherm. The pseudo-second order model provides the best description of the kinetic data. Furthermore, the thermodynamic of adsorption was spontaneous and endothermic. All these results prove that the used adsorbent is environmentally friendly and effective for phosphate adsorption. Graphical abstract