Jordana R. Wood

Macroporous monoliths for trace metal extraction from seawater

The viability of seawater-based uranium recovery depends on the uranium adsorption rate and capacity, since the concentration of uranium in the oceans is relatively low (3.3 μg L−1). An important consideration for a fast adsorption is to maximize the adsorption properties of adsorbents such as surface areas and pore structures, which can greatly improve the kinetics of uranium extraction and the adsorption capacity simultaneously. Following this consideration, macroporous monolith adsorbents were prepared from the copolymerization of acrylonitrile (AN) and N,N′-methylene-bis(acrylamide) (MBAAm) based on a cryogel method using both hydrophobic and hydrophilic monomers. The monolithic sorbents were tested with simulated seawater containing a high uranyl concentration (∼6 ppm) and the uranium adsorption results showed that the adsorption capacities are strongly influenced by the ratio of monomer to the crosslinker, i.e., the density of the amidoxime groups. The preliminary seawater testing indicates the high salinity content of seawater does not hinder the adsorption of uranium.

Towards understanding KOH conditioning of amidoxime-based polymer adsorbents for sequestering uranium from seawater

Conditioning of polymer fiber adsorbents grafted with amidoxime and carboxylic acid groups is necessary to make the materials hydrophilic for sequestering uranium from seawater. Spectroscopic techniques were employed to study the effectiveness of the traditional KOH conditioning method (2.5% KOH at 80 °C) on recently developed high-surface-area amidoxime-based polymer fiber adsorbents developed at Oak Ridge National Laboratory. FTIR spectra reveal that the KOH conditioning process removes the proton from the carboxylic acids and also converts the amidoxime groups to carboxylate groups in the adsorbent. With prolonged KOH treatment (>1 h) at 80 °C, physical damage to the adsorbent material occurs which can lead to a significant reduction in the adsorbents uranium adsorption capability in real seawater during extended exposure times (>21 days). The physical damage to the adsorbent can be minimized by lowering the KOH conditioning temperature. For high-surface-area amidoxime-based adsorbents, 20 min of conditioning in 2.5% KOH at 80 °C or 1 h of conditioning in 2.5% KOH at 60 °C appears sufficient to achieve de-protonation of the carboxylic acid with minimal harmful effects to the adsorbent material. The use of NaOH instead of KOH can also reduce the cost of the base treatment process required for conditioning the amidoxime-based sorbents with minimal loss of adsorption capacity (≤7%).

Milestone Report - Complete New Adsorbent Materials for Marine Testing to Demonstrate 4.5 g-U/kg Adsorbent

This report describes work on the successful completion of Milestone M2FT-14OR03100115 (8/20/2014) entitled, “Complete new adsorbent materials for marine testing to demonstrate 4.5 g-U/kg adsorbent”. This effort is part of the Seawater Uranium Recovery Program, sponsored by the U.S. Department of Energy, Office of Nuclear Energy, and involved the development of new adsorbent materials at the Oak Ridge National Laboratory (ORNL) and marine testing at the Pacific Northwest National Laboratory (PNNL). ORNL has recently developed two new families of fiber adsorbents that have demonstrated uranium adsorption capacities greater than 4.5 g-U/kg adsorbent after marine testing at PNNL. One adsorbent was synthesized by radiation-induced graft polymerization of itaconic acid and acrylonitrile onto high surface area polyethylene fibers followed by amidoximation and base conditioning. This fiber showed a capacity of 4.6 g-U/kg adsorbent in marine testing at PNNL. The second adsorbent was prepared by atom-transfer radical polymerization of t-butyl acrylate and acrylonitrile onto halide-functionalized round fibers followed by amidoximation and base hydrolysis. This fiber demonstrated uranium adsorption capacity of 5.4 g-U/kg adsorbent in marine testing at PNNL.

Milestone Report - Demonstrate Braided Material with 3.5 g U/kg Sorption Capacity under Seawater Testing Condition (Milestone M2FT-15OR0310041 - 1/30/2015)

This report describes work on the successful completion of Milestone M2FT-15OR0310041 (1/30/2015) entitled, Demonstrate braided material with 3.5 g U/kg sorption capacity under seawater testing condition . This effort is part of the Seawater Uranium Recovery Program, sponsored by the U.S. Department of Energy, Office of Nuclear Energy, and involved the development of new adsorbent braided materials at the Oak Ridge National Laboratory (ORNL) and marine testing at the Pacific Northwest National Laboratory (PNNL). ORNL has recently developed four braided fiber adsorbents that have demonstrated uranium adsorption capacities greater than 3.5 g U/kg adsorbent after marine testing at PNNL. The braided adsorbents were synthesized by braiding or leno weaving high surface area polyethylene fibers and conducting radiation-induced graft polymerization of itaconic acid and acrylonitrile monomers onto the braided materials followed by amidoximation and base conditioning. The four braided adsorbents demonstrated capacity values ranging from 3.7 to 4.2 g U/kg adsorbent after 56 days of exposure in natural coastal seawater at 20 oC. All data are normalized to a salinity of 35 psu.

Complete braided adsorbent for marine testing to demonstrate 3g-U/kg-adsorbent

ORNL has manufactured four braided adsorbents that successfully demonstrated uranium adsorption capacities ranging from 3.0-3.6 g-U/kg-adsorbent in marine testing at PNNL. Four new braided and leno woven fabric adsorbents have also been prepared by ORNL and are currently undergoing marine testing at PNNL.