Adsorption behaviors of strontium using macroporous silica based hexagonal tungsten oxide

A novel macroporous silica-based hexagonal tungsten oxide (h-WO₃/SiO₂) with exchangeable sodium cations located in hexagonal tunnel structure was synthesized by a facile hydrothermal treatment of sodium tungstate dihydrate with 1 mol/L HCl solution. Utilization of the h-WO₃/SiO₂ adsorbent to remove aqueous strontium was investigated under the condition of various pH values, contact time, the initial concentration of metal ions, salt ion concentration, and coexisting ions. According to the experimental data, Sr²⁺ adsorption equilibrium was achieved within 15 min in acidic solution, and the maximum removal capacity of Sr²⁺ occurred at pH 4. The kinetic adsorption of Sr²⁺ on h-WO₃/SiO₂ was controlled by pseudo second-order model, and the saturated adsorption of Sr²⁺ on h-WO₃/SiO₂ was better described by Langmuir and Redlich-Peterson isotherm models compared with the Freundlich isotherm model. The distribution coefficient of Sr²⁺ was more than 2000 cm³/g in the presence of Ca²⁺, Mg²⁺, La³⁺, and Eu³⁺, indicating that the h-WO₃/SiO₂ showed excellent selectivity towards Sr²⁺ in pH 4.