Adsorptive removal of phosphate by ZnAlLa ternary layered double hydroxides: Synthesis conditions, adsorption performance, mechanism and reusability

Excessive phosphorus, predominantly in the form of phosphate, poses significant hazards by causing eutrophication, which leads to algal blooms, oxygen depletion, disruptions in aquatic ecosystems, and adverse effects on human health. In this study, ternary ZnAlLa-LDH was synthesized by co-precipitation and then used for phosphate adsorption removal. The results of synthesis conditions impact test indicated that ZnAlLa-LDH synthesized at pH = 8 and La/Al = 1:10 had the pure hydrotalcite structure, the highest yield and lanthanum utilization. It could adsorb about 17% more phosphate than ZnAl-LDH, with a maximum adsorption capacity of 105.42 mg P center dot g- 1 at pH 7. Furthermore, ZnAlLa-LDH demonstrated effective phosphate removal within a pH range of 3 to 6 and exceptional resistance to interference from some common co-existing anions (SO2-4 , NO-3 and Cl-) other than HCO-3 . The adsorption process was a monolayer chemisorption on the heterogeneous surface with each adsorbent molecule occupying 3.73 adsorption sites. Characterization results showed that electrostatic attraction, ligand exchange, ion exchange and surface precipitation jointly achieved phosphate adsorption. ZnAlLaLDH showed promising reusability, with its adsorption capacity remaining above 73% of its initial level after five adsorption-desorption cycles. These findings emphasize the significant capability of ZnAlLa-LDH in removing phosphate from wastewater. This study enhances the P-adsorption performance of ZnAl-LDH through La incorporation while also examining the impact of synthesis conditions, thereby facilitating the practical production and application of LDHs.