Selective solid-phase extraction of uranium by salicylideneimine-functionalized hydrothermal carbon

Highlights: ► Hydrothermal carbon material as solid-phase extractant matrix. ► An excellent hexavalent cation ligand, salicylideneimine, is grafted on the matrix. ► Adsorbent shows high affinity and selectivity to U(VI) in simulated nuclear effluent. ► Process is fast, endothermic, spontaneous, and pseudo-second-order chemisorption. - Abstract: A new salicylideneimine-functionalized hydrothermal-carbon-based solid-phase extractant was developed for the purpose of separating uranium selectively for sustainability of uranium resources. The resulting adsorption material was obtained via hydrothermal carbonization, calcination at mild temperature (573.15 K), amination, and grafting with salicylaldehyde in sequence. Both Fourier transform infrared spectra and elemental analysis proved the successful grafting of salicylideneimine onto hydrothermal carbon matrix. Adsorption behaviors of the extractant on uranium(VI) were investigated by varying pH values of solution, adsorbent amounts, contact times, initial metal concentrations, temperatures, and ionic strengths. An optimum adsorption capacity of 1.10 mmol g−1 (261 mg g−1) for uranium(VI) was obtained at pH 4.3. The present adsorption process obeyed pseudo-second-order model and Langmuir isotherm. Thermodynamic parameters (ΔH = +8.81 kJ mol−1, ΔS = +110 J K−1 mol−1, ΔG = −23.0 kJ mol−1) indicated the adsorption process was endothermic and spontaneous. Results from batch adsorption test in simulated nuclear industrial effluent, containing Cs+, Sr2+, Ba2+, Mn2+, Co2+, Ni2+, Zn2+, La3+, Ce3+, Nd3+, Sm3+, and Gd3+, showed the adsorbent could separate uranium(VI) from those competitive ions with high selectivity. The adsorbent might be promising for use in certain key steps in any future sustainable nuclear fuel cycle.