AUTHOR=Zhang Shaoyang , Xie Fazhi , Tang Zhi , Zhao Tianhui , Fang Mengyuan , Giesy John P. 

TITLE=Adsorption of Phosphate by Surface Precipitation on Lanthanum Carbonate Through In Situ Anion Substitution Reactions

JOURNAL=Frontiers in Environmental Science

VOLUME=Volume 10 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/environmental-science/articles/10.3389/fenvs.2022.858258

DOI=10.3389/fenvs.2022.858258

ISSN=2296-665X

ABSTRACT=<p>Efficient removal of phosphate (PO<sub>4</sub><sup>3−</sup>) is the main solution to control eutrophication. In this study, lanthanum carbonate (La<sub>2</sub>(CO<sub>3</sub>)<sub>3</sub>) was the adsorbent of choice for the removal of PO<sub>4</sub><sup>3−</sup>. Both adsorption isotherm and thermodynamic were investigated. La<sub>2</sub>(CO<sub>3</sub>)<sub>3</sub> was an effective adsorbent for the removal of phosphate (PO<sub>4</sub><sup>3−</sup> or H<sub>2</sub>PO<sup>4−</sup>) under weak acidic conditions (pH = 2.0–6.0); the maximum adsorption amount was 106.6 mg g<sup>−1</sup> at pH 2.9. The pH<sub>zpc</sub> of La<sub>2</sub>(CO<sub>3</sub>)<sub>3</sub> changed from 2.1 to 6.5 prior to and after adsorption of PO<sub>4</sub><sup>3−</sup>. The adsorption of PO<sub>4</sub><sup>3−</sup> on the surfaces of La<sub>2</sub>(CO<sub>3</sub>)<sub>3</sub> was an endothermic process. With the increase of anions, the adsorption efficiency of PO<sub>4</sub><sup>3-</sup> decreased. The presence of natural organic matter also inhibited the adsorption of PO<sub>4</sub><sup>3−</sup>, but the interference was weaker than that of anions. The mechanisms of adsorption were investigated by various techniques including Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), powder X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Based on the results obtained using XPS, during the adsorption process of PO<sub>4</sub><sup>3−</sup> on La<sub>2</sub>(CO<sub>3</sub>)<sub>3</sub>, La<sup>3+</sup> was released and could precipitate with PO<sub>4</sub><sup>3−</sup> or H<sub>2</sub>PO<sub>4</sub><sup>−</sup> under weak acidic conditions (pH = 2.0–4.0). Adsorption was dominated by <italic>in situ</italic> substitution reactions between CO<sub>3</sub><sup>2−</sup> and H<sub>2</sub>PO<sub>4</sub><sup>−</sup> or HPO<sub>4</sub><sup>2−</sup>. This study provides a useful reference and potential material for the removal of PO<sub>4</sub><sup>3−</sup> in aquatic environments.</p>