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.