Dewatering Spent Ion-Exchange Resins with Supercritical CO₂

ABSTRACT

A process for dewatering spent ion exchange resins (gel and porous) used in nuclear power plants by supercritical CO₂ (sCO₂) is described. The amount of water removed by sCO₂ is much higher than that expected from solubility considerations alone. Water from gel-type resins is both dissolved by and emulsified in sCO₂. Emulsification also occurs in the absence of solids when water alone is contacted by sCO₂. It is not a factor for microporous resins where an additional mechanism, viscous fingering, is involved. It appears that bulk water is emulsifiable but not if it is held in pores. Dewatering via viscous fingering has been previously invoked for matrices such as wood and sludge. The resins can be dewatered and dried with sequential batches of sCO₂ at sub-boiling temperatures. The CO₂ can then be potentially reused after expansion and separation from the entrained water. Partial decompression of the water-laden sCO₂ would lead to cooling, which would drop the water solubility substantially. A reduction of temperature from 90 ^oC to 65^oC reduces the solubility of water in sCO₂ by a factor of five. The condensed water could then be separated with a hydrocyclone. The footprint of sCO₂ is much smaller than the conventional drying process. The energy costs are also much lower because evaporation of water is avoided.

KEYWORDS:

• Ion-exchange
• resin
• supercritical CO₂
• nuclear
• solubility
• viscous fingering

Acknowledgments

This work was funded by the US Department of Energy.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The work was supported by the US Department of Energy U.S. Department of Energy .