Greg Klunder, a chemist in LLNL's Forensic Science Center, examines a uranium ore concentrate sample with the aid of a near-infrared spectrometer. (Credit: Steve Wampler / LLNL)A team of Lawrence Livermore National Laboratory (LLNL) researchers has pioneered the use of a long-standing technology—near-infrared spectrometry—for analyzing the chemical composition and determining the origin of uranium samples.
In a paper published as the cover story in the September edition of Applied Spectroscopy, the Laboratory scientists describe the first reported use of near-infrared spectrometry to study the chemical properties of uranium ore concentrates (UOC), also called yellowcake.
Yellowcake (also called urania) is a kind of uranium concentrate powder obtained from leach solutions, in an intermediate step in the processing of uranium ores. Yellowcake concentrates are prepared by various extraction and refining methods, depending on the types of ores. Typically, yellowcakes are obtained through the milling and chemical processing of uranium ore forming a coarse powder which has a pungent odor, is insoluble in water and contains about 80% uranium oxide, which melts at approximately 2878 °C (5212.4 °F).Near-infrared spectrometers were first used in industrial applications in the 1950s and have been utilized for medical diagnostics, combustion research, pharmaceuticals and other uses, but not for studying uranium ore concentrates. The instrument measures the color, intensity and wavelength of light or reflected light.
It is believed that this technology could rapidly provide information on the origin of uranium samples to law enforcement officials who interdict smuggled materials and could be useful in preventing future trafficking from those sources.
For years, one of the primary methods used for determining the different types of uranium has been a simple visual color inspection by researchers. However, visual determination is subjective and no chemical information is provided.
“I was recently in a lab with two other researchers looking at uranium ore concentrates,” said Greg Klunder, a chemist in the Lab’s Forensic Science Center and the paper’s lead author. “I saw the sample as gray, another saw it as brownish and a third as green.
“We used a visible near-infrared spectrometer to test the color. In the near-infrared region, we saw a spectrum consistent with chemical information and the thought came to me that we could use this for evaluating uranium ore concentrates.”
In addition to the simple, color-based inspection, several other methods—including X-ray diffraction and mass spectrometry—are used to analyze UOCs, but these techniques require sample preparation that can significantly compromise the uranium samples.
“The rapid non-contact, non-destructive analysis of UOC materials using near-infrared spectroscopy provides a technical scientific basis for the attribution of a sample that is more valuable than the more subjective evaluation of visual color,” the LLNL scientists said in their paper.
“Near-infrared spectroscopy provides chemical speciation information without consuming or contaminating the sample, thereby enabling supplemental and uncompromised subsequent analyses,” they added.
UOCs are produced at mining facilities from the various types of uranium-bearing ores using several processes that can include different reagents, separation procedures and drying conditions. The final UOC products can therefore consist of different material signatures in the uranium, which are important to identify to trace interdicted samples back to their origins.
The authors believe further investigation will be needed to understand other chemical properties of the uranium ores that can be detected with near-infrared spectroscopy and to evaluate the different phases of the ores.
Klunder GL, Plaue JW, Spackman PE, Grant PM, Lindvall RE, & Hutcheon ID (2013). Application of visible/near-infrared reflectance spectroscopy to uranium ore concentrates for nuclear forensic analysis and attribution. Applied spectroscopy, 67 (9), 1049-56 PMID: 24067636
