Uranium today provides almost a fifth of the world’s electricity, and it is an incredibly useful element . Saskatchewan is at the hub of the world’s uranium production, and hosts the largest mine in the world at McArthur River.
Ensuring that mining sites and their surroundings remain clean and healthy is an important focus for Saskatchewan mining companies and researchers alike.
Luckily, natural wetlands at many mining sites may help sequester uranium tailings. Researchers are interested in understanding and enhancing this process in order to make nuclear power generation even cleaner and safer for the environment.
“The wetlands have the ability naturally to immobilize uranium contaminant through binding to natural organic matters and when we understand how this functions we can also start to think about other technologies,” says Dr. Dien Li of the Savannah River National Laboratory based in South Carolina.
Li is devoted to a diverse range of research surrounding mines and contaminated site remediation, which includes the study of groundwater, sediments and the wetlands, nano particle transport in the subsurface, and developing new materials to effectively remove contaminants.
“Natural attenuation may be among the most cost-effective technologies for treatment of U contaminated sites,” Li says, and studying uranium in these wetlands can help best manage wetlands sequestration.
Recently, he and a team of researchers from Savannah River National Laboratory, Savannah River Ecology Laboratory, Princeton University, Guelph University, the University of Saskatchewan, the University of Chicago and the US Environmental Protection Agency completed a careful study of the biogeochemical behavior of uranium in wetland soils.
Using the HXMA beam line at the Canadian Light Source , the team performed X-ray absorption near-edge structure spectroscopy analysis, which allowed them to identify the uranium’s oxidation state, or number of electrons lost.
Electron configuration is key to element bonding, so helps researchers predict whether uranium would bond to organic matter in soil, ultimately locking it in place and reducing contamination.
“Uranium(VI) is normally the more bioavailable state, and causes problems for the environment. Uranium (IV) is not mobile, and is not easily bioavailable,” explains Dr. Li. Using HXMA, Li’s team found that uranium mostly existed in the bioavailable U(VI) state in the SRS wetland sediments; however, it might be bonding to organic carbon atoms in the wetlands, making it immobile.
The impact of wetlands sequestration on U(VI) is good news for the future of uranium site treatment, says Li.
“Understanding the chemical speciation is important to assessing the risk of each contaminated site and to developing new treatment technologies.”
Next, the team plans to confirm their analysis of uranium bonding on a molecular level for an even deeper understanding of uranium treatment.
This work was supported by Department of Energy, Environmental Management and Office of Sciences, the Savannah River Ecology Laboratory, along with work at the Advanced Photon Source, which is supported by the U.S. Department of Energy.
Li, Dien, et al. "Retention and chemical speciation of uranium in an oxidized wetland sediment from the Savannah River Site." Journal of environmental radioactivity (2013).