Ural Federal University: Scientists Have Developed Uranium Extraction Method from Radioactive Waste

Scientists at Ural Federal University have figured out how to process radioactive uranium-containing sludge. They tested the technology described in the Journal of Environmental Chemical Engineering on sludge waste from the storage facility of one of the nuclear industry enterprises. The samples contained gypsum, carbonate and calcium fluoride, silicon oxide, thaumasite – meaning there were a typical chemical composition. The uranium content in the waste was 0.1%. In other words, it was a uranium-containing sludge with a low level of activity. This is exactly the kind of waste accumulated in huge quantities and in need of large-scale recycling.

“We managed to extract uranium suitable for return to nuclear fuel production. Thus, our proposed method allows us to solve several important problems simultaneously when applied on an industrial scale: to process radioactive waste, to obtain valuable uranium, as well as associated useful materials,” explains Ksenia Nalivaiko, the main researcher and co-author of the article, a graduate student and engineer at the Department of Rare Metals and Nanomaterials at UrFU.

This is a brief description of the method. At the first stage of research samples of uranium-containing sludge were subjected to the “classic” method of leaching with sulfuric acid, varying the acid concentration, temperature and time. The researchers found that the most effective uranium leaching from waste is when the sulfuric acid concentration is 200 g/l and the solution temperature is maintained at 80 oC for four hours. In this case the degree of uranium extraction reaches maximum values and amounts to 99.98%.

In addition to the productive solution containing uranium, solid insoluble residues of gypsum, carbonate and calcium fluoride, silicon oxide (thaumasite dissolves completely) are also formed during leaching. In this case, the activity of alpha- and beta-radiation of the insoluble residue is reduced by 2.5-3 times compared to the original composition. Therefore, the insoluble residue can be used in other areas of industry.

At the second stage, samples of the obtained uranium-containing sulfuric acid solution were passed through ion-exchange resins of various industrial grades. Then the resin was washed with distilled water and uranium was desorbed from the saturated ion-exchange resin by a mixed solution of sulfuric acid and ammonium nitrate. Due to this, the uranium concentration increased 3-8 times.

Further neutralization of the concentrated uranium solution resulted in the final concentrated solid uranium precipitate, the so-called yellowcake. Its uranium content was 68.54%, and the isotopic composition of uranium in the precipitate and the content of impurities (sodium, calcium, aluminum, magnesium, iron and others) meet the international quality standard ASTM C967-13.

A group of scientists from the UrFU has received a grant from the Russian Science Foundation to continue research in this area (Project № 22-29-00846 “Behavior of Actinoids during Formation and Subsequent Storage of Solid Radioactive Waste in Subsurface Storage Facilities”).

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