Optimising Mg–La- layered double hydroxide (LDH) molar ratio for maximum phosphate adsorption

Elevated levels of phosphate ions enter the water bodies through wastewater discharges or agricultural runoffs, leading to significant environmental issues such as eutrophication. The use of synthetic layered double hydroxides (LDHs) for the adsorption of phosphate has emerged as a viable approach to mitigate the environmental impact of excess phosphate in water bodies. The study focused on the synthesis of Mg-La-Layered double hydroxide (Mg-La-LDH) for the removal of phosphate ions from wastewater. The Mg-La-LDH was prepared using the co-precipitation method by adjusting the ratios of Mg-La-LDH from 4:1, 3:1, and 2:1. The synthesised material was analysed using FTIR, SEM, BET, XRD, and TGA techniques. The characterization findings showed that different metal ratios may induce structural changes. An increase magnesium ratio caused distortion in the Mg-La-LDH, resulting in lower crystallinity and performance. Batch experiments were conducted, and the optimal condition was found to be at pH 9, the adsorbent dosage of 20 mg in 25 mL of wastewater, constant time of 150 minutes, and initial phosphate ion concentration of 15 mg.L -1 . Under these conditions, a maximum phosphate ion adsorption capacity was found to be 29.00 mg.g -1 . The kinetics, isotherms and co-existing anions and the reusability were studied. The results showed that adsorption mechanisms involved electrostatic attraction, ion exchange and complexation this was verified by the XPS results of before and after adsorption. Mg-La LDH (2:1) demonstrated good selectivity towards phosphate despite the presence of sulphate, chloride, and nitrates at high concentrations. The material may also be used for up to five cycles, with just a 4% drop in adsorption efficiency. This adsorbent shows great potential for removing phosphate from wastewater. • Mg-La-LDH (2:1) synthesised through co-precipitation method exhibited maximum phosphate adsorption of 29.9 mg.g -1 in real wastewater samples. • Phosphate selectivity was demonstrated in the presence of elevated sulphate, nitrate, and chloride concentration. • Adsorption mechanism encompasses electrostatic attraction, ion exchange, and complexation processes.