CO₂ competes with radioactive chemicals for freshwater recovery: Hydrate-based desalination

Here, we introduce CO₂ hydrate-based desalination (CHBD) technology for freshwater recovery from radioactive wastewater, for water particularly containing Cs and Sr. The hydrate equilibrium curves of CO₂ hydrates shift towards lower temperature and higher pressure regions as the concentrations of CsCl and SrCl₂ increase. X-ray diffraction and Raman spectroscopy measurements found that neither CsCl nor SrCl₂ can affect the structure of CO₂ hydrates. The high-pressure micro-differential scanning calorimetric results demonstrate that CO₂ hydrates in the presence of CsCl and SrCl₂ started to dissociate at lower temperatures due to the enrichment of CsCl and SrCl₂ in the remaining solutions. The formation kinetics results indicate that increases in the concentrations of the radioactive chemicals lead to a decrease in the initial reaction rate and sub-cooling temperature. Solid-state nuclear magnetic resonance spectroscopy was utilized to confirm the exclusion of radioactive isotopes from solid gas hydrates. Importantly, the CHBD technology proposed in this study is applicable to radioactive wastewater containing Cs⁺ and Sr²⁺ across broad concentration ranges, spanning from a percent to hundreds of parts per million (ppm), and even sub-ppm levels, with comparable recovery efficiency. This study presents new insights into the potential of environmentally sustainable technologies to overcome the challenges posed by radioactive wastewater.