Development of Novel Method for Rapid Extract of Radionuclides from Solution Using Polymer Ligand Film
Open Access
- Author:
- Rim, Jung Ho
- Graduate Program:
- Nuclear Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 25, 2013
- Committee Members:
- Kenan Unlu, Committee Chair/Co-Chair
Jack Brenizer Jr., Committee Member
Igor Jovanovic, Committee Member
Danny Glynn Sykes, Committee Member
Dominic S Peterson, Special Member
Stephen La Mont, Special Member - Keywords:
- PLF
Actinide
Plutonium
Uranium
Environmental
Extraction
H2DEH[MDP]
HDEHP
Separation - Abstract:
- Accurate and fast determination of the activity of radionuclides in a sample is critical for nuclear forensics and emergency response. Radioanalytical techniques are well established for radionuclides measurement, however, they are slow and labor intensive, requiring extensive radiochemical separations and purification prior to analysis. With these limitations of current methods, there is great interest for a new technique to rapidly process samples. This dissertation describes a new analyte extraction medium called Polymer Ligand Film (PLF) developed to rapidly extract radionuclides. Polymer Ligand Film is a polymer medium with ligands incorporated in its matrix that selectively and rapidly extract analytes from a solution. The main focus of the new technique is to shorten and simplify the procedure necessary to chemically isolate radionuclides for determination by alpha spectrometry or beta counting. Five different ligands were tested for plutonium extraction: bis(2-ethylhexyl) methanediphosphonic acid (H2DEH[MDP]), di(2-ethyl hexyl) phosphoric acid (HDEHP), trialkyl methylammonium chloride (Aliquat-336), 4,4'(5')-di-t-butylcyclohexano 18-crown-6 (DtBuCH18C6), and 2-ethylhexyl 2-ethylhexylphosphonic acid (HEH[EHP]). The ligands that were effective for plutonium extraction further studied for uranium extraction. The two ligands, H2DEH[MDP] and HDEHP, which showed effectiveness in plutonium extraction were extensively studied. The extraction of strontium was exclusively studied with DtBuCH18C6. This particular ligand was effective for strontium separation in resin bead form. However, in PLF form, the ligand became completely ineffective for strontium extraction. The plutonium recovery by PLFs has shown dependency on nitric acid concentration and ligand to total mass ratio. H2DEH[MDP] PLFs performed best with 1:10 and 1:20 ratio PLFs. 50.44% and 47.61% of plutonium were extracted on the surface of PLFs with 1M nitric acid for 1:10 and 1:20 PLF, respectively. HDEHP PLF provided the best combination of alpha spectroscopy resolution and plutonium recovery with 1:5 PLF when used with 0.1M nitric acid. The overall analyte recovery was lower than electrodeposited samples, which typically has recovery above 80%. However, PLF is designed to be a rapid field deployable screening technique and consistency is more important than recovery. PLFs were also tested using blind quality control samples and the activities were accurately measured. It is important to point out that PLFs were consistently susceptible to analytes penetrating and depositing below the surface. The internal radiation within the body of PLF is mostly contained and did not cause excessive self-attenuation and peak broadening in alpha spectroscopy. The analyte penetration issue was beneficial in the destructive analysis. The extra plutonium contained in the PLF body gave additional signal in the analysis. Plutonium was successfully back-extracted from PLF and procedures were established for isotopic analysis by thermal ionization mass spectrometry (TIMS). H2DEH[MDP] PLFs showed few advantages over HDEHP PLFs. H2DEH[MDP] PLFs showed better sample recovery consistency than HDEHP. The sample to sample variation in plutonium recovery was comparable to variation observed with electrodeposited samples. H2DEH[MDP] PLF was also capable of co-extracting or selectively extracting plutonium over uranium depending on the PLF composition. With 1:5 H2DEH[MDP] PLF, about 23% of plutonium and 20% uranium were co-extracted. On the other hand, both 1:10 and 1:20 PLFs were preferably extracting plutonium over uranium at the same condition. H2DEH[MDP] PLF was tested with environmental samples to fully understand the capabilities and limitations of the PLF in relevant environments. The extraction system was very effective in extracting plutonium from environmental water collected from Mortandad Canyon at Los Alamos National Laboratory with minimal sample processing. Soil samples were tougher to process than the water samples. Analytes were first leached from the soil matrixes using nitric acid before processing with PLF. This approach had a limitation in extracting plutonium using PLF. The soil samples from Mortandad Canyon, which are about 1% iron by weight, were effectively processed with the PLF system. Only 5.11x10-3% of iron from soil was leached using 1M nitric acid. The Rocky Flats soils with higher iron content (2.6%) were unsuccessfully processed with PLF for plutonium extraction. The leached solutions from the soil with higher iron concentration had dark reddish color, which indicates a presence of large concentration of iron. The large amount of iron in leached solution interfered and rendered PLF ineffective for analyte extraction. No detectable activities were measured from Rocky Flats samples processed with PLFs. Even with certain limitations of the PLF extraction system, this technique was able to considerably decrease the sample analysis time. The entire environmental sample was analyzed within one to two days. The decrease in time can be attributed to the fact that PLF is replacing column chromatography and electrodeposition with a single step for preparing alpha spectrometry samples. The two-step process of column chromatography and electrodeposition takes a couple days to a week to complete depending on the sample. The decrease in time and the simplified procedure make this technique a unique solution for application to nuclear forensics and emergency response. A large number of samples can be quickly analyzed and selective samples can be further analyzed with more sensitive techniques based on the initial data. A procedure was established to perform TIMS analysis and plutonium isotopics were measured in a number of PLF samples. The deployment of a PLF system as a screening method will greatly reduce a total analysis time required to gain meaningful isotopic data for the nuclear forensics application.