Study Finds Efficient Way to Filter Nuclear Wastewater

Syllabus: GS3/Science and Technology

Context

• A new study published in Environmental Science & Technology may finally offer a way to efficiently clean tritiated water.
  • The research team, from across China, achieved this using a metal-organic framework, work on which won the Nobel Prize for chemistry last year.

About

• In 2023, Japan began releasing treated wastewater from the ruined Fukushimanuclear power plant into the Pacific Ocean. 
  • The water had been filtered to remove most heavy radioactive elements, yet one particular contaminant remained: tritium.
  • Tritium is easily absorbed by the bodies of living creatures and rapidly distributed via blood.
• Tritium is a radioactive isotope of hydrogen. When it bonds with oxygen, it forms tritiated water, or HTO.
  • Because tritiated water is chemically almost identical to regular water, it is extremely difficult to separate the two. 
  • For many decades, officials in the global nuclear industry have opted to dilute tritiated water, i.e. mixing it in large quantities of regular water.

Current Methods of Removing Tritium

• The current most practical way to remove tritium from tritiated water is water distillation, i.e. boiling water and separating the components based on their slightly different boiling points.
  • But the difference is so feeble that operators need a distillation tower hundreds of metres tall, which is expensive, uses large amounts of energy, and impractical for the millions of tonnes of water stored at Fukushima.
• Current distillation towers use systems called packings, these are the materials inside the tower that provide surfaces where steam and liquid can interact. 
  • Until now, these packings were passive: they just sat there and let gravity do the work. 
• In the new study, the researchers made the packing material ‘active’.
  • They coated a stainless-steel mesh with a metal-organic framework called NH2-MIL-101(Cr). A metal-organic framework is like a microscopic sponge. 
  • Adding NH2-MIL-101(Cr) increased the available  area of the packing by 32-fold. 
  • The chromium-oxygen clusters inside the framework ‘grabbed’ tritium atoms from the liquid and swapped them with regular hydrogen atoms, with nitrogen and hydrogen attachments also facilitating this swapping.

• Outcome: The modified packing achieved a separation efficiency of 42.5 theoretical plates per meter, a record-setting figure in the world of chemical engineering.
  • At an industrial height of 10 m, the new material would be 134-times more effective than the current best-reported material.
  • It is also one-million-times more effective than the standard commercial packings in the industry today.
• Significance: 
  • This strategy provides a new approach for improving the detritiation of tritiated water and reducing tritium releases to natural water bodies.
  • The results highlight the potential of programmable porous materials to address challenging isotope-contaminant separations.

Nobel Prize in Chemistry 2025

• Susumu Kitagawa, Richard Robson and Omar Yaghi were awarded the Nobel Prize in Chemistry 2025.
• It was awarded for discovering and creating a class of materials, called metal-organic frameworks (MOF).
• Metal Organic Frameworks: MOFs are crystalline structures in which metal ions serve as nodes and organic molecules as connectors. 
  • The resulting structure can have enormous internal surface areas — thousands of square metres per gram — and their pores can be customised to attract or hold specific molecules.

• MOFs form a three-dimensional network with large, porous cavities; this design allows gases and liquids to flow through, making MOFs highly adaptable for various applications. 
  • By carefully choosing the building blocks, researchers can control the size and shape of the cavities and the chemical environment within. 
  • As a result, MOFs are among the most versatile materials ever created.

The unique properties of MOFs have led to their application in various fields:

• Water harvesting: MOFs can extract water from dry air, offering a potential solution for water-scarce regions.
• Pollutant Removal: They can filter out harmful substances like PFAS from water, addressing environmental contamination.
• Carbon capture: MOFs are effective in capturing carbon dioxide, aiding in efforts to mitigate climate change.
• Hydrogen storage: Their porous nature allows for the safe storage of hydrogen, crucial for clean energy applications.

Source: TH