Preparation and Characterization of a High-Efficient Potassium Adsorbent H8Nb22O59·8H2O

Abstract

The adsorbent of H8Nb22O59·8H2O and the precursor of Rb8Nb22O59 were characterized by X-ray diffraction (XRD), Thermogravimetric and differential scanning calorimetry (TG-DSC), and scanning electron microscope (SEM). The ion-exchange properties of H8Nb22O59·8H2O for Na+ and K+ were also investigated, including the saturation adsorptive capacity, distribution coefficients and separation factor. The results show that the crystallinity of Rb8Nb22O59 was affected by the calcination temperature. The structure of Rb8Nb22O59 was not changed when Rb+ was extracted from Rb8Nb22O59, indicating that this process was topotactical. The calcination temperature and pH value had a significant influence on the ion-exchange capacities of H8Nb22O59·8H2O for Na+ and K+. Specifically, the uptake amouts of Na+ and K+ by H8Nb22O59·8H2O increased with the calcination temperature, while the distribution coefficients of Na+ and K+ for H8Nb22O59·8H2O increased with the pH value. Moreover, the separation factors for K+ was larger than that for Na+ and it increased with the increase of calcination temperature. Overall, the improvement of the crystallinity of H8Nb22O59·8H2O was beneficial to its selectivity for K+.