Different La/Fe oxide composites for efficient phosphate removal from wastewater: Properties and mechanisms

Metal oxides are widely used in the removal of oxygen-containing anions from the aqueous phase, and multi-metallic oxides were promising adsorbents for removal performance. In order to explore the effect of different La/Fe oxide composites (LF) on phosphate adsorption, three bimetallic composite oxides of La/Fe were prepared by citric acid sol-gel method at 600, 700 and 800 oC (named LF-600, LF-700 and LF-800). According to adsorption experiments, the adsorption capacity was changed obviously with the temperature increasing. The maximum adsorption capacity was 77.08, 41.17 and 14.58 mg g−1 at pH 7.0 of LF-600, LF-700 and LF-800, respectively. The specific surface area (SBET) and the crystal type are the main factors affecting the adsorption capacity. With the temperature increasing, the SBET reduced and the crystal phase was LaOCl and Fe2O3 of LF-600, LaOCl, LaFeO3 and Fe2O3 of LF-700, and LaFeO3 and LaOCl of LF-800. In addition, the adsorption capacities decreased obviously with the increase of pH and the addition of CO32−. The FTIR, XRD and XPS analysis proved that the adsorption mechanism mainly was surface precipitation, electrostatic attraction and complexation, and complexation was the main adsorption mechanism.