Synthesis of Novel Co-Polymers Using Ionizing Radiation Grafting Methods for the Extraction of Uranium from Seawater
Dietz, Travis Cameron
Al-Sheikhly, Mohamad I
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The world’s oceans contain a relatively uniform uranium concentration of 3 μg/L. While this is an exceedingly small concentration, the quantity of uranium throughout the oceans is about 1000 times higher than the quantity in known terrestrial deposits. To take advantage of this immense resource, radiation grafting techniques were used to attach uranium-chelating monomers to durable polymer substrates. Three novel, uranium extracting co-polymer systems have been fabricated through this process and characterized. Three different compound classes were explored for their ability to extract uranium, specifically phosphates, oxalates, and azos. These classes displayed characteristics that provide advantages to the technology over state-of-the-art systems. For the phosphates and oxalates, monomers of these classes containing allyl groups were radiation grafted onto a polymer in a single step. For the azos, a chemical precursor containing a vinyl group was initially radiation grafted to a polymer. The azo compound was then chemically attached to the functionalized polymer surface. For effective seawater deployment, a polymer substrate was chosen as an inexpensive, reusable platform for extraction. While different fabric substrates were tested, high surface area (14 m^2/g) nylon 6 fabric was chosen for its durability and its capacity for radiation grafting. Direct and indirect radiation induced graft polymerization methods were used in this work. For direct grafting, the nylon 6 fabric was immersed in the monomer solution and irradiated. However, for indirect grafting, only the fabric was irradiated followed by the immediate introduction of the monomer solution. All of these experiments were conducted under anaerobic conditions to prevent the reaction of oxygen with the radiolytically-produced, carbon-centered free radicals. The grafted fabrics were characterized for attachment of the monomer and their ability to extract uranium. The degree of surface grafting was determined through attenuated total reflectance Fourier transform infrared spectroscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy, among other techniques. Electron paramagnetic resonance spectroscopy was used to determine radical decay kinetics in the polymer substrate. Pulse radiolysis was used to elucidate the polymerization reaction kinetics of certain monomers. These fabrics were then exposed to uranium-doped seawater solutions and the extraction capacities of the grafted materials were determined.