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Description
99mTc is very important for medical practice, and efforts to develop the best procedure for the production of its parent 99Mo for the subsequent use in 99mTc generators are being made for more than four decades. For this purpose, a composite ceramic target containing HEU dioxide and a filler metallic powder (Al, Mg, etc.) has been irradiated in a high-flux reactor to obtain concentrate solu-tion for fission Mo recovery by sorption, extraction or precipitation. However, this method has not been recommended by IAEA because of nuclear nonproliferation. Another option is to use irradia-tion of LEU dioxide without filler in commercial-level fluxes and to rise 99Mo concentrating capabil-ity as an alternative method to 98Mo or 100Mo irradiation.
Extraction of Mo, U and certain FP from HNO3 solutions with 0.2% solutions of higher hy-droxamic acids (HA) in alcohols poorly soluble in water has been studied for 99Mo concentrate pro-duction from solutions of different enriched U targets, including those of 3% 235UO2.
The process chemistry of Mo has been supposed for both steps of Mo interphase transfer. Mo extraction by the solvent containing caprinohydroxamic acid (CHA) or laurylhydroxamic acid (LHA), is a slow process limited by first-order reaction in aqueous phase.
The DMo decreases with increase of HNO3 concentration which is typical of cation-exchange processes. The log–log plot of DMo vs. total CHA or LHA concentration is slightly S-shaped, but it is linear with the slope of 2.0 for DMo after deduction of Mo extraction by alcohol vs. free HA con-centration. DMo in the case of CHA is near indifferent for alcohol content, but it has the slope of 1.0 for LHA.
Mo backwashing has been performed by interphase autocatalytic thermo-chemical HA oxidiz-ing destruction with 5 mol/L HNO3 at 95 oC in combination with Mo complexing in aqueous phase by a salt-free reagents. Alkaline scrubbing has been chosen for final regeneration of the alcohol.
The rig trials included dissolution of U-Al model or real targets in 8 mol/L HNO3 containing 0.2 g/L Hg and 0.2 g/L HF at 95 oC, allowing further I2 and Ru compounds air stripping. The fur-ther concentrating process was tested in counter-current and batch variants and the latter was found to be rather effective.
Mo extraction recovery was performed using 27 mmol/L CHA in 20% n-decanol with Isopar-M in 3 steps: extraction, scrubbing and backwashing in the vessels of decreasing volume. The simulate feed contained, mol/L: HNO3 -1.2; Al – 1.2; Fe - 5∙10-3; U – 0.11; Hg - 1∙10-3, 239Pu – 1.4∙10-4, Mo – 3.2∙10-5, as well as 15 MBq/L 99Mo, 5.2 MBq/L 125I and 4.1 MBq/L 239Np.
The achieved total concentrating factor was 180 at process duration 2 h. Mo decontamination factors were for: U ~ 1.5∙106, 125I ~ 850, 239Pu > 105, 239Np > 106, Al > 106, Fe - 4.6∙104, Hg ~ 2∙104.
The feasibility study has indicated that the compact extraction flowsheet and simple batch equipment are suitable for profitable 99Mo recovery from standard 3-5% 235UO2 targets. Final Mo decontamination for Tc generator production can be performed by sorption and/or by sublimation.
Patents RU:
1. 2 522 544 (2014);
2. 2 575 028 (2016);
3. 2 624 920 (2017)
