Kaolin-iron cross-linked alginate beads for efficient phosphate removal from water: An initiation towards sustainable treatment of domestic and hydroponic wastewaters

This research aims to investigate the process of removing phosphate ions from water using iron cross-linked alginate beads incorporating kaolin (Alg@K). The prepared adsorbents were characterized using a range of analytical techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared (FT-IR) spectroscopy, and nitrogen adsorption-desorption analysis. Alg@K demonstrated effective adsorption of phosphate. An optimal dosage of Alg@K (4 g/L) was determined to reach a maximum adsorption capacity of 20.70 mg/g at a concentration of 150 mg/L after 4 h. Alg@K beads achieved a complete removal of phosphate for phosphate concentrations (<50 mg/L). The pH of the solutions significantly influenced the adsorption mechanism. The kinetic data fitted well with the pseudosecond-order kinetic model, indicating that chemisorption played a crucial role in the removal of phosphate. Isotherm studies confirmed that Alg@K beads followed the Langmuir model, with a high coefficient of determination. The maximum theoretical capacity of Alg@K, calculated using the Langmuir model, was 22.51 mg/g. Moreover, the adsorption of phosphate by Alg@K composites was insignificantly affected by co-existing ions, while the removal capacities experienced a reduction of approximately 9% with the existence of NO3- (2 mol/L). Adsorption/desorption experiments demonstrated the successful reusability of Alg@K beads over multiple cycles, indicating that the incorporation of kaolin significantly enhanced the reuse of this adsorbent. These beads showed potential for the recovery of phosphate from domestic and hydroponic wastewaters and subsequently have the potential to be utilized as slow-release fertilizers or soil amendments.