Adsorption behavior of self-loading bayberry tannin resin for UO22+ with surface phenolic hydroxyl groups

In this study, self-polymerization of bayberry tannin and formaldehyde condensation were used to prepare a self-loading tannin resin (STR). The environmental conditions for UO22+ capture by STR were thoroughly investigated; the experimental results indicated that the UO22+ adsorption capacity of STR could reach 691.9 mg/g under optimal adsorption conditions. The mechanism of UO22+ capture by STR was studied using scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The results showed that STR possessed a significant number of phenolic hydroxyl groups, which enabled the reduction of U(VI) in water to U(IV). Subsequently, stable chelation complexes were formed by filling vacant orbitals of uranium through the lone electron pair of oxygen, resulting in the formation of O = U = O structural motifs, which facilitated the effective capture of UO22+ in water. Moreover, the evaluation of the performance of STR in low-concentration UO22+ extraction from seawater revealed its favorable UO22+ removal capacity, even in simulated seawater conditions. These findings highlight the substantial potential of STR for practical applications in uranium remediation.