Adsorption characteristics of strontium on synthesized antimony silicate

Radioactive strontium (90Sr) is one of the major contaminants in low-level radioactive wastewaters from nuclear power plants. Antimony silicate is regarded as a selective inorganic adsorbent for 90Sr removal. In this paper, a safe method was developed to prepare antimony silicate adsorbents. In the synthetic process, stable and low-toxic antimony trichloride (SbCl3) was used as an antimony source instead of volatile antimony pentachloride (SbCl5). Besides an Sb-rich phase with well-crystalized pyrochlore structure, an Si-rich phase with amorphous structure can be detected, which may facilitate strontium adsorption due to its large specific surface area. The batch experiments demonstrate that the synthesized material can offer a favorable adsorption of Sr(II) over a broad pH range of 1.2–11 and a wide concentration range of co-existing ions. The highest Kd value amounts to nearly 108 mL/g at an Si/Sb ratio of 2.9. Calcium ions have a significant negative influence on strontium adsorption. The Kd value drops to 102 mL/g at a Ca2+ concentration of 0.1 M. The kinetic performance of Sr(II) adsorption onto antimony silicate follows the pseudo-second-order model and the adsorption isotherms coincide well with the Freundlich model. Moreover, the thermodynamic study reveals that the adsorption is an endothermic and spontaneous process.