Prof. HUANG Qunying's team from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences, in collaboration with Prof. NING Shunyan's team from South China University, developed a novel silica-based adsorbent for the highly selective separation of strontium (Sr) from acidic medium.

The results were published in Journal of Hazardous Materials.

Radioactive strontium, known as ⁹⁰Sr, is of concern because it's highly toxic both radiologically and biochemically. When high-level liquid waste (HLLW) is processed through vitrification, the heat released from the decay of ⁹⁰Sr can cause problems. This heat can destabilize the material in which it's contained, potentially leading to the release of other radioactive substances. However, ⁹⁰Sr can also be reused as a special radioactive or heat source, which can help reduce the amount of waste to be disposed of with lower overall costs.

To address the above issues, the research team developed a novel porous adsorbent called CEPA@SBA-15-APTES. This adsorbent is made by modifying mesoporous silica to selectively separate Sr. They studied how this adsorbent behaves when exposed to different environments using Sr-stable nuclides. They found that the adsorption reached equilibrium in 30 minutes in a solution with a low concentration of nitric acid (HNO₃) and in only five minutes in a solution with a higher concentration of HNO₃.

Importantly, the adsorbent showed excellent selectivity for Sr in 3 M HNO₃ simulated HLLW solution. The mechanism of Sr adsorption differs depending on the acidity of the solution: ion exchange occurs in solutions with low HNO₃ concentration, while coordination occurs in solutions with higher HNO₃ concentration.

This study develops a novel material for the efficient separation of strontium, which is a reference for the selective separation and recovery of radionuclides.

Schematic illustration of CEPA@SBA-15-APTES preparation process. (Image by ZHANG Shichang) 

Adsorption selectivity: (a) Effect of four competing ions on Sr adsorption in 10^-6 M HNO₃ solution; (b) Adsorption of different metal ions in the HNO₃ solutions. (Image by ZHANG Shichang)