Chromatography Determines Rare Earth Elements in Uranium Ore

Chromatography is used in many different types of analysis. Food, pharmaceutical and environmental are areas traditionally associated with chromatographic analysis. But chromatography is also used in many other different types of analysis. A paper published in the journal Minerals demonstrates this as it discusses the use of chromatography in the realm of nuclear forensics.

Uranium in the earth and sea

Uranium is a naturally occurring element that is found in minerals. Uranium is a radioactive element that is found in many different isotopes - the two main isotopes are U-238 (99.27%) and U-235 (0.72%). All uranium isotopes are radioactive and undergo fission to other elements. Alongside thorium and potassium, uranium contributes to the Earth’s natural radioactivity.

Uranium is a relatively common element in the Earth’s crust - almost as common as tin or zinc. It is found in most rocks and in seawater, albeit at very low concentrations. The known uranium resources on Earth have increased in recent years due to mineral exploration. The primary uranium ore is uraninite, an ore previously known as pitchblende. Many of the high-grade uranium deposits lie in close proximity to unconformities - a type of interface between two deposits for example between sedimentary and metamorphic deposits.

Forensics of nuclear materials

The illegal and illicit trafficking of nuclear materials is a potential threat to peace and nuclear stability in the world. Nuclear forensics involves the analysis and investigation of nuclear materials. The aim of the investigation is to find evidence for the source, trafficking and enrichment of the material. Samples can be taken from the material itself or dust from in the vicinity of the nuclear facility. Radioactive debris from a nuclear explosion would also be a sample source.

Uranium ore concentrate is a product of the nuclear fuel cycle. And it is uranium ore concentrates that are likely to be traded or smuggled. One of the methods used to determine origin of a sample is to analyse the rare earth elements that can be found in the ore concentrate. Although many of the impurities are removed in the production process, the rare earth elements persist.

Analysing the REEs

The rare-earth elements are chemical elements that are not all that rare - being found in good supply in the Earth’s crust. It has been found that specific ratios of rare earth elements are found in certain locations in the crust. And if that location coincides with a site from which uranium is mined then the rare earth signature can be used to locate the uranium ore’s source.

Researchers use liquid chromatography to separate the rare earth elements from the uranium ore concentrate with the resulting target analytes measured by inductively coupled plasma-mass spectrometry (ICP-MS). The use of MS to analyse samples is discussed in the article, Recent Advances to Conquer Analytical Challenges with High-Resolution, Accurate Mass Spectrometry. The method developed was effective at quantifying rare earth elements in uranium ores.