Preparation of silica gel bound crown ether and its extraction performance towards zirconium and hafnium

Abstract

A new silica gel bound Dibenzo-18-crown-6(DB-18-C-6) solid extractant (SGN18) was synthesized, and its structure was characterized by FT-IR, TGA, BET and Element analysis. The adsorption and separation behaviors of SGN18 on Zr(IV) and Hf(IV) were investigated in terms of acidity, shaking time and initial concentrations. The complexes of [Zr(DB-18-C-6)] and [Hf(DB-18-C-6)] were investigated by DFT theory to predict the extraction ability of DB-18-C-6 for Zr(IV) and Hf(IV). The results showed that DB-18-C-6 was successfully grafted on the silica gel with a satisfactory grafting degree (17.16wt.%). Analysis on kinetic data indicated that the rate decisive adsorption step was interparticle diffusion for Zr(IV), and film diffusion for Hf(IV), as well as Langmuir isotherm mode was only applicable for Zr(IV). The separation factor of SGN18 for Zr(IV) was greater than for Hf(IV), which was highly consistent with DFT calculation results that the binding energy of DB-18-C-6 with Zr(IV) was greater than Hf(IV). All the experiment outcome proved that the adsorption capacity of SGN18 for Zr(IV) was stronger than the Hf(IV).