Efficient removal and selective recovery of phosphorus by calcined La-doped layered double hydroxides

Abstract

Advanced phosphate removal technologies are necessary to mitigate eutrophication problems. Since lanthanum and phosphate have a strong affinity for each other, lanthanum-doped composite materials are widely applied in phosphate removal. In this study, Mg/Fe/La LDOs (MFL) was synthesized successfully by calcination, which considerably enhanced the adsorption capacity of phosphate by reconstructing and compositing metal oxide compounds. MFL-1/10-350 was characterized by XRD, BET, zeta potential, SEM, TGA, XPS, and FTIR. The MFL-1/10-350 showed a typical BET surface area of 154.61 m2/g and was composed of Mg, Fe, La, and O. MFL-1/10-350 exhibited a high Langmuir maximum adsorption capacity of 123.15 mg P/g at 25 °C and strong selectivity for phosphate. The mechanisms of phosphate adsorption on the samples are mainly electrostatic interactions, surface complexation effects, and ion exchange. When 0.5 g/L of MFL-1/10-350 was added to real wastewater with a phosphate content of 3.6 mg P/L, the phosphate concentration quickly decreased to less than 0.12 mg P/L. Phosphorus-adsorbed LDOs (LDOs-P) can provide phosphorus continuously to promote rice growth. The composite material of MFL-1/10-350 was harmless to the growth of rice during the experiment. The results show that MFL-1/10-350 is an ideal material for the effective adsorption and recovery of phosphorus. This provides a possible way for phosphorus removal and recycling in water.