Study On The Preparation Of Several Uranium Adsorbents Supported By Cotton Cloth

With the development and utilization of nuclear energy, there is an increasing shortage of land uranium resources, but the ocean contains abundant uranium resources, which means that extraction of uranium from seawater can ensure the continuous supply of nuclear energy.Meanwhile, the nuclear industry will produce a large amount of radioactive waste liquid which causes environmental pollution and harms human health. Therefore it is of great scientific and practical significance to extract uranium from seawater and radioactive waste water in an effective way. This thesis uses cotton cloth as the material of substrate via hydrothermal method on which coats basic magnesium carbonate, ZnO and Mg-Al hydrotalcite. Furthermore the adsorption properties of corresponding adsorbents were studied and discussed deeply. Besides HNO₃-H₂O₂ and HNO₃-NH3·H₂O two eluating process were designed in order to realize uranium enrichment and reuse of raw materials.The carboxyl group modified cotton fiber surface was coated by basic magnesium carbonate using magnesium nitrate as the source of magnesium and urea as precipitating agent via hydrothermal method. SEM showed that basic magnesium carbonate on cotton cloth after ultrasonic is not shedding from the cotton fiber, indicating a strong adhesion strength between the basic magnesium carbonate and cotton fiber. This is the result of the in situ growth by complexation of carboxyl and magnesium ions and the adsorption growth by electrostatic attraction. TEM observation showed that the granular basic magnesium carbonate formed by stacking with porous lamella with abundant pore structure. The results of uranium adsorption experiments show that prepared material has a good adsorption performance whose maximum adsorption capacity is 367.26 mg/g. The optimal adsorption pH value was 5.0, the adsorption rate was fast and the adsorption reached saturated after 60 minutes. The adsorption process conforms to the Freundlich isothermal adsorption model, followed by the pseudo-second-order kinetic model. The adsorption mechanism was explored that crystallization water of basic magnesium carbonate hydrolyzed to produce hydrogen ions which had replacement with uranyl ions in aqueous solution.The surface of cotton fibers were coated with a layer of ZnO nanorod arrays using a two-step seed-growing method. XRD characterization shows that zinc oxide had a very high crystallinity and purity. TEM images show that zinc oxide nanorods are hexagon, and diameters of the rods are not regular. Besides the phenomenon of graft growth was observed.The growth mechanism of ZnO was preliminarily discussed which could be described that growth elements ?[Zn?OH?4]2-? moved to seeds on the cotton fibers, and then dehydrated to form zinc oxide and preferred growing to rods. The uranium adsorption experiments showed that the maximum adsorption capacity is 428.76 mg/g, the optimal adsorption pH is 5.0, the rate of adsorption is a bit high and which chould reach saturated in 40 minutes. The adsorption process conforms Langmuir isothermal adsorption model and pseudo-second-order kinetic model, which confirms that uranium adsorption by ZnO is monolayer adsorption and the control steps of adsorption are chemical. Thermodynamic data shows that the adsorption process was endothermic and spontaneous.Cotton fibers were coated with a layer of lamellar Mg-Al hydrotalcite using magnesium nitrate,aluminum nitrate and urea as material by hydrothermal method as adsorption materials. SEM showed that Mg-Al hydrotalcite on cotton cloth after ultrasonic is not shedding from the cotton fiber, indicating a strong adhesion strength between the Mg-Al hydrotalcite and cotton fiber. TEM characterization shows that hydrotalcite film layer is composed of stacking thinner sheets. Due to pore forming effect of water vapor and carbon dioxide the hydrotalcite has abundant pore structure. The uranium adsorption experiments showed that the maximum adsorption capacity is 176.3 mg/g, the optimal adsorption pH is 6.0 and the adsorption took 6 h to reach adsorption equilibrium,but the adsorption rate is a bit low. The adsorption mechanism was preliminarily explored which was considered as the complexation of hydroxyl in interlayer hydrotalcite and uranyl ions.