Graduate Thesis Or Dissertation
 

The adsorption of uranium ions from seawater

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  • The adsorption of uranium ions from seawater could be of importance as reserves of uranium are depleted. The structure, chemical state, and concentration of uranium in seawater have been previously determined. Uranium exists as a charged ion, UO₂(CO₃)₃⁴⁻. The concentration in seawater is 3.3 parts per billion. Previous studies with titanium hydroxide as an adsorber have shown promising results, but the expense and reproducibility in synthesizing titanium hydroxide pose serious problems. Other types of adsorbents were tested in this study to determine which were potentially good adsorbents of uranium. Tests were carried out at the Oregon State University Marine Science Center using natural seawater. After exposure, samples were tested for uranium ion uptake by neutron activation analysis. A variety of ion exchange resins and adsorbents gave poor results. Silica gels gave results which led to further investigations. Methods for the preparation of silica gels are described. These methods were varied to alter the structure of the gels prepared. The gels were then tested for their ability to adsorb uranium ions from seawater. The gels and methods of preparation giving the best results were found. Commercially prepared gels gave the best results of any of the silica gels. Amounts adsorbed ranged from 3 to 5 ug uranium per gram silica gel. These commercial gels were used in a further study to determine the ability to reuse silica gels for the adsorption of uranium ions. Surface areas and pore sizes were measured after each cycle of exposure to seawater. Results demonstrated poorer adsorption as the cycles proceeded. Surface areas decreased markedly and pores became larger. The changes in surface areas and pore size distributions were related to the ability of the materials to adsorb uranium ions from seawater. Future success in adsorbing uranium will depend on obtaining an adsorbent that retains its physical structure and can be used repeatedly.
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