In the future, nuclear clean-up workers may be getting help from some surprising sources. None of these three methods are in widespread use right now, but they show promise:
- Scientists have discovered that a type of algae can precipitate strontium into crystals. This could lead to better nuclear clean-up techniques, potentially sequestering radioactive strontium-90 from tainted water into crystalline form, which is easier to contain.
- The algae, called C. moniliferum, collects strontium in sulfate-rich vacuoles, and because strontium and barium have low solubility in sulfate solutions, they precipitate out of solution as crystals.
What’s the Context: The danger of strontium-90 is that it is chemically similar to calcium, and so can be taken up into milk, bones, and other tissues. Nuclear waste and spills can contain significant amounts of strontium; C. moniliferum is especially helpful because it can precipitate strontium but leave calcium alone (calcium is different enough from barium that the bacteria doesn’t crystallize it).
Not So Fast: Scientists don’t yet know how well the algae can withstand radioactivity, which could potentially put a damper on this clean-up method. Now, the scientists would like to find ways of increasing sulphate levels in the environment, which may in turn increase the ability of the algae to crystallize strontium.
2) Green Rust
- Other researchers have found that green rust, a highly reactive variety of rust, immobilizes radioactive neptunium. “Our study shows that even the safest [mechanical] encapsulation of radioactive waste could be made safer if radioactive waste canisters are buried in a place where green rust will form,” University of Copenhagen geochemist Bo C. Christiansen said in a press release.
- Being highly reactive, when green rust encounters radioactive neptunium, the researchers think that it either reacts with neptunium, converting it into its insoluble, solid form, or incorporates neptunium into its mineral structure, thereby preventing it from spreading.
What’s the Context:
- The green rust technique is seen as a preventative measure to limit the damage caused by future radioactive waste spills. The technique, such as it is, involves building nuclear-storage facilities in areas that are rich in green rust.
- With neptunium’s long half-life, it will still be around in five million years, which may be a lot longer than our nuclear-storage tanks last.
Not So Fast: Because it’s so reactive, green rust is rarely found in the natural environment. (Though the researchers hope to find ways of increasing concentrations.)
- E. coli, a ubiquitous and well-studied bacterium (see Carl Zimmer’s book Microcosm: E. Coli and the New Science of Life), may potentially be used to recover uranium from polluted waters. “We have shown that an economic, scalable process for uranium recovery is possible,” Birmingham University scientist Lynne Macaskie said.
- The researchers found that E. coli breaks down a chemical called inositol phosphate—a cheap chemical that could be added to the cleanup site—freeing the phosphate molecules. These phosphate molecules bind to uranium, precipitating uranium-phosphate on the bacteria’s cells, which can then be removed for uranium harvesting.
What’s the Context: The E. coli process actually dates back to 1995, but more recently the researchers started using inexpensive inositol phosphate, which makes the process six times more effective.
Not So Fast: For some countries that have ample and cheap supplies of uranium, such as the U.S., this uranium recycling may not be so popular. But it would be especially useful for countries like England. Harvesting and recycling uranium could make nuclear energy even greener.
Krejci, M. R., et al. “Selective Sequestration of Strontium in Desmid Green Algae by Biogenic Co-precipitation with Barite.” ChemSusChem. doi:10.1002/cssc.201000448.
Christiansen, B.C. et al. “Neptunyl (Np) interaction with green rust, GRNa,SO4.” Geochimica et Cosmochimica Acta. doi:10.1016/j.gca.2010.12.003.
Paterson-Beedle, M. et al. “Biorecovery of Uranium from Minewaters into Pure Mineral Product at the Expense of Plant Wastes.” Advanced Materials Research. 10.4028/www.scientific.net/AMR.71-73.621.
Image: Algae crystallizing strontium. Courtesy Minna R. Krejci et al.