Phosphate removal from aqueous solution by Fe-La binary (hydr)oxides: characterizations and mechanisms.

Abstract

In this study, Fe-La binary (hydr)oxides were prepared by a co-precipitation method for phosphate removal. Various techniques, including secondary electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), powder X-ray diffraction (p-XRD), and Brunauer-Emmett-Teller (BET) surface area analysis, were employed to characterize the synthesized Fe-La binary (hydr)oxides. Batch experiments indicated that the performance of phosphate removal by Fe-La binary (hydr)oxides was excellent and increased with increasing the concentrations of La. The kinetics study showed that the adsorption was rapid and described better by the pseudo-second-order equation. The maximum adsorption capacities of Fe/La 3:1, Fe/La 1:1, and Fe/La 1:3 binary (hydr)oxides at pH 4.0 calculated by Langmuir model were 49.02, 69.44, and 136.99 mg/g, respectively. The uptake of phosphate was highly affected by solution pH and significantly reduced with the increase of pH value. The analyses of p-XRD, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) suggested that the predominant mechanisms of phosphate removal involved surface hydroxyl exchange reactions and co-precipitation of released La3+ and phosphate ions, which resulted into the formation of amorphous phase of rhabdophane (LaPO4·0.5H2O). The results show great potential for the application on the treatment of phosphate decontamination for their high efficiency of phosphate removal.