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 hex- agonal 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 ca- pacity 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 St2＋ 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.