SBIR-STTR Award

High-surface-area amidoxime and carboxylic acid grafted polymer fibers show high adsorption capacities for uranium. They are currently considered the most efficient sorbent materials for sequestering uranium from seawater. Durability of the sorbent is a crucial determining factor of the economic feasibility of utilizing this type of new sorbent for commercial mining of uranium from the ocean. Prior to adsorption applications, the amidoxime-based polymer sorbents is typically treated with a strong KOH solution conditioning step) to make the material hydrophilic by removing proton from the grafted carboxylic acid. After uranium adsorption, hydrochloric acid is traditionally used to elution uranium from the sorbent. Again, the sorbent must undergo a KOH reconditioning process for its repeated use. The KOH conditioning and acid elution processes are too harsh for the high-surface-area polymer fibers resulting in lower uranium adsorption capacity and limited durability for their repeated use. LCW Technologies will develop new sorbent conditioning processes and selective uranium elution methods to achieve high uranium recovery efficiency with significant improvement of the adsorption capability and durability of the sorbent. These new processes would lower the cost for extracting uranium from seawater utilizing the high-surface-area amidoxime-based polymer sorbent materials. A recent cover-page article published in Dalton Transactions 2014, 43, 10713-10718) shows that selective elution of uranium from an amidoxime-carboxylate grafted polymer sorbent can be achieved using 1 M Na2CO3 and 0.1 M H2O2 with the formation of an extremely stable and water-soluble uranyl- peroxo-carbonato complex. Loss of uranium adsorption capacity using the Na2CO3-H2O2 elution is about 3% per cycle as compared to a 20% per cycle reduction in uranium sorption capacity utilizing the 0.5 M HCl elution. Additionally, in the Na2CO3-H2O2 elution method there is no need for the KOH reconditioning of the sorbent for reuse resulting in further cost savings. Elution in carbonate solutions is typically performed in a pH range close to that of natural seawater and hence is least harmful to the sorbent materials. New sorbent conditioning methods will also be developed using mild alkaline solutions to reduce potential damages to the sorbent material and to increase uranium adsorption capacity. LCW Supercritical Technologies is committed to develop new technologies to make uranium from seawater commercially feasible. The proposed Phase 1 SBIR project will produce new condition and elution processes which are crucial for the economic viability of commercial extraction of uranium from seawater.

Sea water contains about 3 parts per billion of uranium. With a total ocean volume of approximately 1.3×109 km3, there is at least 4.5 billion tons of uranium in seawater which is about 1000 times the amount of uranium known to exist in terrestrial ores. Developing efficient and reusable adsorbent for economic extraction of uranium from seawater is an active research area in the USA and other countries in the world. In the Phase I study, we discovered that acrylic fiber (yarn) can be converted to an amidoxime and carboxylic acid containing polymer adsorbent which is selective, efficient and reusable for extraction of uranium from seawater. The adsorbent shows a uranium adsorption capacity greater than other adsorbents reported in the literature in real seawater tests. The SBIR Phase II project will test the polymer adsorbent in kilogram quantities in a scaled up operation to produce 10’s gram quantities of uranium oxide from seawater. The proposed uranium from sea water experiments will be carried out using an outdoor circulating raceway flume facility available at PNNL’s Marine Sciences Laboratory in Sequim, Washington. The scale up technology demonstration is necessary for us to obtain data for developing an industrial scale process and to perform cost analysis of the process for production of uranium from seawater. Initial cost analysis based on the data obtained from small sample (50100 mg) tests is promising suggesting that this new technology could make uranium production from seawater economically competitive with the land based uranium mining methods. Key Words – Uranium Production, Seawater, Polymer Adsorbent. A novel uranium selective adsorbent derived from common yarn is capable of extracting uranium from seawater with a high efficiency. The new extraction technology could make uranium production from seawater economically competitive with the land based uranium mining.