Study On The Preparation Of Potassium Ion Sieve Membrane Of High Sio₂/al₂o₃ And Its Application Performance

Chemical resources are rich in seawater, and the total reserves of potassium are 500 billion tones.From the perspective of sustainable development, the extraction of potash from seawater has bright prospects.The defects such as discontinuity, long cycle and large ground occupation of the granular potassium ion sieves can be overcome through using potassium ion sieve membrane which is suitable for continuous separation. So studying on the noval potassium ion sieve membrane has important application value for improving the market competitiveness for extraction of potash from seawater.The conditions of the high SiO2/AlO3 potassium ion sieve synthesis were studied. Using NaAlO2 and solbule glass (27.9% SiO2) as raw materials, KOH as the alkali source, and tetrabutyl ammonium bromide, n-butylamine, isopropyl alcohol, caprolactam as template agents,the effects of the SiO2/Al2O3,alkalinity, template agents, crystallization temperature and crystallization time on the crystalline structure of ion sieve, production and exchange capacity were investigated. The optimum synthesis condition for ion sieve synthesis is:using tetrabutyl ammonium bromide as template agent, with the molar ratio of 6.68K2O:19.3SiO2:1Al2O3:624H2O,at 120℃for 12h. The morphology of the ion sieve is phillipsite-K, its exchange capacity for potassium from the seawater is about 56.96mg/g, and crystal of phillipsite-K is crossed radiation.When tetrabutyl ammonium bromide was used as template agent, the potassium ion sieve membrane was synthesized with the molar ratio of 6.68K2O:19.3SiO2:1Al2O3: 624H2O by the secondary growth hydrothermal method. The effects of properties of the a-Al2O3 tube, times of hydrothermal synthesis, synthesis temperature, the calcination temperature and the rate on the potassium ion sieve membrane were studied.The optimum synthesis condition for ion sieve membrane synthesis is:with the above molar ratio,the ion sieve membrane is prepared at 150℃for 12h. The ion sieve membrane synthesized for three and four times,the results of SEM show that the potassium ion sieve membrane is continuous, dense and integrated with around 15μm in thickness.The results of single gas permeability determination show that the ideal separation factors of the ion sieve membrane synthesized for three and four times are 6.13and 7.43 respectively, which is larger than Knudsen diffusion ratio of the H2/N2, so the ion sieve membrane is integrity without defects.The separation selectivity of the ion sieve membranes to K+, Na+, Ca2+ and Mg2+ were measured by ion exchange experiments.The separation factors of K+/Na+, K+/Ca2+, K+/Mg2+are respectively equal to 224.78,+8,and+8.It was found that the potassium ion sieve membranes have the higher selectivity to K+, and completely block the calcium and magnesium cation through the membrane. And the separation factor of ion sieve membrane is greatly enhanced compared with the selection separation coefficient of the phillipsite-K powder. The results of the above studies show that the potassium ion sieve membrane can separate K+ from Ca2+,Mg2+,Na+ selectively, and show a good prospect in extracting potassium from the seawater.