Selective Adsorption of Hafnium Using SBA-15 Mesoporous Silica for Efficient Separation from Zirconium

The separation of zirconium (Zr) and hafnium (Hf) represents a critical challenge in the nuclear industry, where Hf-selective adsorbents are essential for sustainable separation. Here, mesoporous silica SBA-15 synthesized via a soft-template strategy was employed as an Hf-selective adsorbent for Zr/Hf separation. Under optimal conditions, SBA-15 demonstrated pronounced selectivity for Hf4+, achieving a separation coefficient (βHf/Zr) of 2.9. The adsorption behavior for both Zr4+ and Hf4+ on SBA-15 was well described by the Langmuir isotherm and pseudo-second-order kinetic models, indicating that the adsorption of Zr4+ and Hf4+ is a monolayer chemisorption. Thermodynamic analysis further confirms that the adsorption process is spontaneous and endothermic. Combined with characterizations and density functional theory calculations, the abundant intrinsic silanol groups (−Si–OH) on SBA-15 were determined as the primary adsorption sites. Furthermore, the binding energy between Hf4+ and SBA-15 (−9.69 eV) is markedly lower than that between Zr4+ and SBA-15 (−9.40 eV), driving the preferential adsorption of Hf4+. Compared with Zr, the expanded 5d orbital distribution of Hf facilitates more effective bonding with the 2p orbitals of oxygen in silanol groups. This work offers a promising green and sustainable approach for the selective separation of Hf from Zr/Hf mixtures, with potential applications in both scientific research and industry.