Adsorption of Phosphate Ions on Novel Mg/Fe/Al Hydroxides (MFA) Prepared at Different Mg2+/Fe3+/Al3+ Ratios

In this study, we prepared novel Mg/Fe/Al hydroxides (MFA series: denoted by MFA1, MFA2, MF, and MA) and investigated their properties using scanning electron microscopy, X-ray diffraction, the specific surface area, and amount of hydroxyl groups. Additionally, the phosphate adsorption capabilities of the MFA series or Fe–Mg type hydrotalcites (FHT3.0 and FHT5.0) were evaluated by examining the effects of the solution pH and contact time, and analyzing the adsorption isotherm and desorption characteristics. In MFA1, a strong correlation exists between the amount of adsorbed phosphate ions and surface hydroxyl groups, with a correlation coefficient of 0.95. The adsorption kinetics data fitted using the pseudo-second-order model performs better than the pseudo-first-order model. The adsorption isotherm data were also fitted using both the Freundlich and Langmuir models. Finally, the phosphate ions adsorbed on the MFA1 surfaces were desorbed using sodium hydroxide solution. These results indicate that MFA1 offers great potential for phosphate ion adsorption from aqueous solutions and functions as a renewable adsorbent.