Enhancing U(VI) removal from highly acidic wastewater through the synergistic effect of diethylenetriaminepenta(methylenephosphonic) acid and meso-SiO 2 on nanosized γ-Fe 2 O 3

Wastewater from uranium mining activities is highly acidic and contains uranium, thereby posing severe risks to the ecological environment and human health. Accordingly, uranium purification is extremely crucial. Herein, we delicately designed a novel adsorbent of diethylenetriaminepenta(methylenephosphonic) acid (DTPMP) and meso-SiO 2 modified gamma-Fe2O3 2 O 3 (gamma-Fe2O3@SiO2@DTPMP, 2 O 3 @SiO 2 @DTPMP, denoted as FSD), and found that the adsorbent can remarkably boost the removal performance of U(VI) under highly acidic conditions. The removal efficiencies of U (VI) by FSD are 90.26 % and 99.81 % in strong acidic solutions of pH = 1.0 and pH = 2.0, respectively, which are much higher than most of the reported adsorbents. Importantly, FSD exhibits high adsorption capacity (51.45 mg/g) and excellent anti-interference, even the wastewater stream contained a lot of organic substances ( e.g. , fulvic acid), cations ( e.g. , K+, + , Na+, + , Mg2+, 2 + , NH4+, 4 + , Zn2+, 2 + , Co2+, 2 + , etc.), radioactive nuclides ( e.g. , Cs+ + and Sr2+). 2 + ). After five cycles, the adsorption efficiency and desorption efficiency of FSD only reduced by 8.83 % and 9.61 %, respectively, which are mainly attributed to the unique structures and good chemical stability of FSD. The removal of U(VI) by FSD is a heterogeneous adsorption process which is dominated by chemical adsorption, mainly involving surface coordination complexation. Multiwfn wavefunction and VMD programs based on density functional theory (DFT) further analyzed and visualized the interaction sites and relative strengths of reactions. The results of detailed characterization analysis and theoretical calculations confirmed that the highly efficient U(VI) removal by FSD is mainly ascribed to the strong coordination of the phosphate groups and amino nitrogen atoms in DTPMP with UO22+. 2 2 + . Therefore, this study provides a promising strategy for the removal of U (VI) in strongly acidic wastewater.