Adsorption of tungsten ion with a novel Fe-Mg type hydrotalcite prepared at different Mg2+/Fe3+ ratios

Abstract

A novel Fe-Mg type hydrotalcite at different Mg2+/Fe3+ ratio (Fe-HT3.0 and Fe-HT5.0) were prepared, and their properties were investigated by scanning electron microscopy, X-ray diffraction analysis, electron probe microanalysis, specific surface area, and binding energy studies. In addition, the adsorption capability of tungsten onto Fe-HT3.0 and Fe-HT5.0 was evaluated. The amount of tungsten adsorbed onto Fe-HT3.0 and Fe-HT5.0 increased with increasing temperatures. The results of the adsorption isotherm studies suggested that tungsten adsorption can be well described by both the Freundlich (R2: 0.895–0.998) and Langmuir (R2: 0.890–0.998) equations. The tungsten adsorbed onto the adsorbent surface was confirmed by electron probe microanalysis and binding energy. The obtained data on thermodynamic parameters showed a decrease in ΔG with the increase in temperature, which indicated that tungsten adsorption was spontaneous. The adsorption of tungsten onto Fe-HT3.0 and Fe-HT5.0 reached equilibrium within 3 and 10h, respectively, and the adsorption kinetic data fit the pseudo-second-order kinetic model better than the pseudo-first-order kinetic model. The optimal pH condition for the adsorption of tungsten onto Fe-HT3.0 and Fe-HT5.0 is approximately 2.0. The results of this study indicate that the adsorption mechanism of tungsten onto Fe-HT3.0 and Fe-HT5.0 involves ion exchange, electrostatic attraction, and surface inner-sphere complex formation between tungsten ion and hydroxide ion. Finally, tungsten adsorbed onto the Fe-HT3.0 and Fe-HT5.0 surfaces was desorbed by sodium hydroxide solution at different concentrations. Collectively, these results suggest that Fe-HT3.0 and Fe-HT5.0 can be useful for the adsorption and recovery of tungsten from aqueous solutions.