Scientific Basis for Efficient Extraction of Uranium from Seawater, II: Fundamental Thermodynamic and Structural Studies

Abstract

The development of an efficient and economical system for extracting uranium from seawater could lead to an essentially limitless source of fuel for nuclear reactors. Currently, the most promising technology for recovering uranium from seawater involves the use of polymeric sorbents functionalized with the amidoxime moiety. However, competition of amidoxime sorbents with carbonate for uranium, indiscriminate sorption of other seawater cations, seawater temperature, and sorbent durability affect the efficiency and cost of this technology. Insights from thermodynamic and structural studies have proved to be powerful tools for addressing these issues and aiding the development of more effective sorbents for uranium. We summarize herein the results of these studies and discuss their implications for the extraction of uranium from seawater.

Temperature Dependence of Uranium and Vanadium Adsorption on Amidoxime‐Based Adsorbents in Natural Seawater

“…The amidoxime ligand, which has a high stability constant for the uranyl ion, also has a strong affinity for several other metal ions in seawater, including V, Fe, Zn, Cu, and Ni ,,,. This multi‐element affinity indicates that a competition exists between seawater cations and binding sites of the amidoxime‐based adsorbents.…”

“…Endrizzi and Rao later suggested that the dominant U(VI) species in seawater is Ca 2 UO 2 (CO 3 ) 3(aq) , with two relatively minor complexes, (MgUO 2 (CO 3 ) 3 2− and CaUO 2 (CO 3 ) 3 2− ) arising from the high concentrations of Ca and Mg in seawater. Using Ca 2 UO 2 (CO 3 ) 3(aq) to recalculate the Δ H of the U(VI)‐glutarimidedioxime complexation, a corrected Δ H of 30 kJ mol −1 was proposed . In addition, from the Δ H of complexation between U(VI) and glutardiamidoxime and the thermodynamic data on Ca 2 UO 2 (CO 3 ) 3(aq) , we estimated that the major reaction between U(VI) and glutardiamidoxime under seawater conditions has a Δ H of 57 kJ mol −1 ,…”

The enhanced uranyl–amidoxime binding by the electron-donating substituents

“…) is desired. 3 In the past few decades, amidoxime (AO) has been screened as the most promising candidate, and various absorption materials bearing this ligand or its derivatives have been developed and applied in both mimic seawater and eld experiments. [4][5][6] To date, sequestering uranium from ocean at the industrial level is still limited.…”

Thermodynamic Studies to Support Extraction of Uranium from Seawater

“…Additionally, the 51 V NMR spectrum of a D 2 O solution of Na[V(L) 2 ]·2H 2 O(cr) was collected to help confirm the assignment of the vanadium signal and is also shown in Figure 2 (spectrum e). As Figure 2 shows, the 51 V NMR spectrum of the initial solution (a) in the absence of glutaroimide-dioxime shows the peaks for the vanadates (VO 4 3-and HVO 4 2-) at δ = -537, -561 ppm. The vanadate peak () has broad shoulders indicating the spin-spin coupling with 17 O (see the inset for spectrum a in Figure 2).…”