Apr 27, 2020
Reducing waste and time – Novel approach allows for rapid isotope production for medical diagnostics
Life Sciences, Chemical Process, Diagnostics/Biomarker
- ⁹⁹ᵐTc as one of the most important medical radioisotopes
- Novel dry-chemical separation of molybdenum and uranium
- More environmentally friendly production with less toxic waste
With its wide application range in nuclear medicine, technetium-99m (⁹⁹ᵐTc) is one of the most important medical radioisotopes. Used by doctors and scientists for diagnostic and research purposes into organ structures and function, ⁹⁹ᵐTc arises through the ß-decay of its parent isotope molybdenum-99 (⁹⁹Mo) which is a fission byproduct of the neutron irradiation of targets enriched in uranium-235 (235U) in nuclear reactor. Due to its short half-life of 66 hrs, ⁹⁹Mo production has to happen on a regular basis and is tightly scheduled to ensure continuous availability and not risk interruptions impacting patient care. ⁹⁹ᵐTc is directly extracted on-site in hospitals in specialized generators from a decaying sample of ⁹⁹Mo. By emitting γ-rays, it can then be used for radiodiagnostics after injection into patients. Significant global efforts are underway to ensure a reliable continuous supply chain of ⁹⁹Mo and ⁹⁹ᵐTc. In addition, the call for a more environmentally friendly solution has intensified in the last years as the target conversion from highly to low enriched uranium comes at the cost of a significant increase in radioactive waste. Following neutron irradiation, uranium targets have to be dissolved to recover and purify ⁹⁹Mo. Depending on the uranium target used, the dissolution process involves the use of an alkaline or acid solution. In both cases, the waste management presents a considerable problem, since the accumulating waste from ⁹⁹Mo production contains ca. 97% of the enriched uranium from the original targets¹.
The present innovation describes a dry-chemical process allowing for the rapid separation of molybdenum from uranium by converting them to their corresponding metal hexafluorides. The multi-stage process originates with a gas phase mixture of MoF₆ and UF₆ which is fed into a liquid or supercritical fluid phase to dissolve both metal fluorides. By photoreduction UF₆ is precipitated to its pentafluoride UF₅. Separating UF₅ as a solid phase yields a solution containing the desired MoF₆. The solvent itself is highly volatile, allowing for its evaporation after the separation process. The inventive separation has the advantage over the established wet chemical separation by producing smaller quantities of acidic radioactive waste which results in a costly and elaborate disposal.
- Rapid dry chemical separation of molybdenum and uranium
- Reduced acidic waste production compared to wet chemical procedure
- Opportunity to use separation approach for recycling of unspent uranium from uranium-molybdenum alloys currently under development
Proof of concept