One-pot hydrothermal synthesis of NaLa(CO3)2 decorated magnetic biochar for efficient phosphate removal from water: Kinetics, isotherms, thermodynamics, mechanisms and reusability exploration

Phosphate elimination is vital for the remediation of eutrophication to avoid deterioration of water quality. Lanthanum (La) based adsorbents have been proven to have the potential for the removal of phosphate in contaminated water because of its strong affinity for phosphate. Herein, we report the high efficiency of NaLa (CO3)(2) decorated magnetic biochar described as La-Fe-BC for the elimination of phosphate in water. The adsorbent was simply and facilely prepared through a one-pot hydrothermal method, and the characterization results confirmed the effective activation of biochar by KHCO3 and the successful infusion of NaLa(CO3)(2) and Fe3O4 onto the surface of La-Fe-BC. The batch adsorption studies revealed that the La-Fe-BC exhibited an excellent monolayer phosphate uptake of 330.86 mg/g over a wide pH range of 3.0-8.0, undisturbed affinity to phosphate in the presence of various co-existing ions (e.g. NO3-, SO42- and Cl-), prominent magnetic separation efficacy of 91%, superior reusability with more than 88% of desorption efficiency and 65% of phosphate uptake maintained after five adsorption-desorption recycles. Thermodynamic results presented a negative value of Delta G(0), clearly indicative of a favorable and spontaneous reaction, while the positive values of Delta H-0 and Delta S-0 affirmed the endothermic characteristic of phosphate uptake onto La-Fe-BC with an increase in randomness. The La groups (i.e. La(CO3)(2)(-) and La(HCO3)(2)(+)) on La-Fe-BC are believed to enhance the phosphate binding owing to a combination of electrostatic attraction and inner-sphere complexation via ligand exchange. Overall, this study enables the omnidirectional enhancement of tailored adsorbents to the depollution of phosphate contaminated water.