Electrochemical‐Mediated Regenerable Fe^II Active Sites for Efficient Uranium Extraction at Ultra‐Low Cell Voltage

Abstract

Nano‐reduced iron (NRI) is a promising uranium adsorbent due to its strong reducibility and good selectivity, but it still faces the challenges of slow kinetics, limited and non‐renewable active sites. In this work, we realized high efficiency uranium extraction under ultra‐low cell voltage (−0.1 V) in seawater with 20 ppm UO2(NO3)2 solution by coupling electrochemical mediated FeII/FeIII redox and uranium extraction. The adsorption capacity and extraction efficiency of NRI after electrochemical uranium extraction (EUE) could reach 452 mg/g and 99.1 %, respectively. Combined with quasi‐operando/operando characterization technologies, we clarified the mechanism of EUE and revealed that continuously regenerating FeII active sites by electroreduction could significantly enhance the property of EUE. This work here provides a new electrochemical mediated and low energy consumption uranium extraction strategy which also provides a reference for other metal resource recovery.

Strengthening Fe(II)/Fe(III) Dynamic Cycling by Surface Sulfation to Achieve Efficient Electrochemical Uranium Extraction at Ultralow Cell Voltage

“…Compared with the original S-NRI, due to the chemical interaction between Fe–OH and UO 2 2+ , the peak position of M–OH bonds after EUE shifted to the direction of low binding energy by about 0.58 eV (Figure c). However, for S-NRI after EUE, the decreased value of M–OH content is far lower than that of NRI, which also indirectly indicates that the Fe–SO 4 2– bond is easier to interact with UO 2 2+ , which can work as main active sites. The Fe 2p XPS spectra for S-NRI were split into three peaks, which were classified as Fe(0), Fe­(II), and Fe­(III), respectively (Figure d).…”

“…For S-NRI in a seawater electrolyte with 20 ppm UO 2 (NO 3 ) 2 , the electrochemical method can almost reach adsorption equilibrium in just 3 h, and the extraction efficiency and capacity can reach 90.00% and 357.30 mg/g, respectively. However, for the NRI adsorbent, the extraction efficiency and capacity after 3 h are only 60.00% and 211.70 mg/g, respectively, and reaching adsorption equilibrium also takes 12 h. The faster electrochemical extraction kinetics for S-NRI compared to NRI could be attributed to the stronger interaction between M–SO 4 2– bonds and UO 2 2+ than M–OH bonds . Higher extraction capacity and efficiency for S-NRI could be ascribed to the fact that Fe–SO 4 2– bonds promoted the Fe­(II)/Fe­(III) redox cycle, hastened the electron transfer between Fe­(II) and UO 2 2+ , and promoted the regeneration of Fe­(II) active sites .…”

“…Compared with the original S-NRI, due to the chemical interaction between Fe−OH and UO 2 2+ , the peak position of M−OH bonds after EUE shifted to the direction of low binding energy by about 0.58 eV (Figure 2c). However, for S-NRI after EUE, the decreased value of M−OH content is far lower than that of NRI, 24 which also indirectly indicates that the Fe−SO 4…”

“…21−23 Our previous research has confirmed that electrochemically mediated Fe(II)/Fe(III) redox-coupled uranium extraction can significantly reduce the cell voltage of EUE. 24 How to strengthen the Fe(II)/Fe(III) redox cycle process to achieve the rapid electron transfer and regeneration of active sites and how to regulate the surface structure to enhance the selective adsorption ability of uranyl ions are crucial for EUE. Nanoreduced iron (NRI) is a good uranium adsorbent but its application is limited due to its disadvantages of easy deactivation and agglomeration; thus, the selectivity and stability for uranium still need to be further improved.…”

“…At present, electrochemical uranium extraction (EUE) has shown great potential due to its large adsorption capacity and fast adsorption rate. − The pulse electrochemical method can effectively realize the redistribution of uranium ions on the electrode surface, improve the selectivity of uranium ions, and show a large adsorption capacity. , However, these electrochemical strategies still face the challenge of high cell voltage, and it is difficult to balance cell voltage, adsorption capacity, and selectivity, especially in the complex seawater environment. − Our previous research has confirmed that electrochemically mediated Fe­(II)/Fe­(III) redox-coupled uranium extraction can significantly reduce the cell voltage of EUE . How to strengthen the Fe­(II)/Fe­(III) redox cycle process to achieve the rapid electron transfer and regeneration of active sites and how to regulate the surface structure to enhance the selective adsorption ability of uranyl ions are crucial for EUE.…”