Utilizing Bubbles
The Korea Atomic Energy Research Institute (KAERI) announced on Sept. 14 that it has developed a process to mass-produce bentonite, a high-quality material used to dispose of spent nuclear fuel. “If this material is supplied domestically through a localized process, it will save the Korean economy about 600 billion won,” the institute said.
The process technology has been recognized for its excellence and patented in Korea and abroad including in Japan, France, Canada and China so far this year. In the future, a large amount of bentonite will be needed as a buffer material when operating a high-level waste disposal site. KAERI is also considering its application to various industries other than radioactive waste disposal through further empirical studies.
Dr. Kim Bong-joo of the Storage and Disposal Verification Division at KAERI has successfully developed a production process that can raise the quality of Korean-made bentonite to the same level as foreign products. Bentonite is a type of clay that can be found everywhere. It is often used as a waterproofing material in the civil engineering field because it has the property of greatly expanding in volume when it absorbs water.
Bentonite is also a versatile industrial material that is used as a refining and decolorizing agent, desiccant, and a raw material for cosmetics and pharmaceuticals due to its strong ability to adsorb and remove impurities.
Bentonite is also a key material in the field of spent nuclear fuel disposal. Spent nuclear fuel is a high-level waste. Korea is considering a deep geological repository where spent nuclear fuel is isolated hundreds of meters underground. The material is used as a buffer around spent fuel containers to prevent groundwater from entering and prevent radioactive materials from leaving the spent fuel containers. That is to say, nuclear waste experts can utilize bentonite’s excellent waterproofing and radionuclide adsorption capabilities.
Bentonite’s waterproofing and adsorption capabilities are enhanced by the large volume of montmorillonite (MMT) in it. MMT is a natural clay mineral belonging to the smectite group. Montmorillonite is a natural clay resource that has a structure with very thin layers, allowing it to absorb more water and expand between layers than other clays. However, Korean-made bentonite has a very small amount of montmorillonite content compared to foreign bentonite, impeding its industrial utilization. Therefore, high-quality bentonite with high montmorillonite content has been imported to Korea from overseas, including China, the United States, India, Australia, and Mongolia.
To improve the quality of Korean-made bentonite, KAERI researchers focused on increasing montmorillonite content using a wet process and a physical screening process.
First of all, bentonite was mixed with water to form sludge and the mineral particles were dispersed using ultrasound. Relatively lighter montmorillonite particles were then separated by flotation, which involves adding fine air bubbles to the sludge to float the lighter particles. This specialized process raised the content of montmorillonite in bentonite from 60 percent to 94 percent.
In August, KAERI developed a flotation screening device that can mass-produce high-quality bentonite by continuing this process and has finished preparing for its demonstration.