Study On Prepration Dan Application Of The High-Efficient Potassium Adsorbent H₈Nb₂₂O₅₉·8H₂O

High-purity sodium chloride (99.99%) could be extensively applied on food industry, medicine, the medical field, etc. Very similar properties for Na+ and K+ results in difficulty for separation K+, which is mixed from the preparation of sodium chloride solution. It is impossible to obtain a high-purity sodium chloride though conventional methods, such as precipitation, ion exchange, and extraction, due to the low selectivity for K+. In order to obtain high-purity sodium chloride, more attention is focused on the ion-sieve compound with high selectivity for K+ in recent decades.Ion-sieve compound is a metal oxide porous crystals (MOPCS), which is usually synthesized through the template method. And the ion-sieve compound with the unique structure can be obtained by topotactically removing the template ions from inorganic compound with the template ions, which is calcined at the high temperature. The ion-sieve compound show high selectivity for specific ion depending on the template ion, so it can be used for the removal of specific ion in the presence of an excess of other competitive species, and the systhesis of the potassium adsorbent can provide a new method for the preparation of the high-purity sodium chloride.According to the similar properties of Na+ and K+, the ion-sieve adsorbent H8Nb22O59-8H2O can be synthesized though extracting Rb+ from RbgNb22O59, which is calcined at the high temperature. The adsorbent H8Nb22O59·8H2O and the precursor Rb8Nb22O59 were studied by X-ray diffraction (XRD), Thermogravimetric and differential scanning calorimetry (TG-DSC), and scanning electron microscope (SEM), respectively, and the ion-exchange properties of the adsorbent H8Nb22O59·8H2O for Na+ and K+ were investigated by saturation adsorptive capacity, distribution coefficients Kd, and separation factor a, respectively. The crystallinity of Rb8Nb22O59 was affected by the calciantion temperature and duration, and the change of the structure was not observed during the extraction of Rb+from Rb8Nb22O59, indicating that this process was topotactical. The calciantion temperature and the pH values of solutions had a significant influence on the separation of H8Nb22O59·8H2O for Na+ and K+, and the affinity of H8Nb22O598H2O for Na+ and K+increased with the calcination temperature, but the selectivity for K+is only improved. Distribution coefficients of H8Nb22O59·8H2O for Na+ and K+ increased with the pH value, but separation factor was different. The improvement of the crystallinity was beneficial to the selectivity for K+. The used HgNb22O59·8H2O still has high selectivity for K+, and the adsorptive equilibrium can be completed during 48 h. The adsorbent HgNb22O59·8H2O shows markedly high selectivity for the adsorption of K+, and ion-sieve exchanger Rb8Nb22O59 is the promising potassium adsorbent for purification of the sodium chloride solution.