Innovative Condition and Elution Processes for Sequestering Uranium from Seawater

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.