Fundamental Chemistry Related to the Separations and Coordination of Actinium-225, Thorium-227, and Technetium-99
Date of Degree
James F. Wishart
Inorganic Chemistry | Radiochemistry
Radiochemistry, Ionic Liquids, Isotope production, Electrochemistry, Technetium
This work explores the fundamental chemistry of actinium, thorium, and technetium in an effort to develop methodologies which help to address complications specific to each of these elements. Developing fundamental knowledge in inorganic chemistry has the power to meaningfully address a number of real world problems. By using simple systems and experiments like following an electron or changing the solvent system, we are able to gain invaluable information which can be used to address major issues.
Actinium-225 (t½: 9.92 d) is an alpha-emitting radionuclide with nuclear properties well suited for alpha therapy of malignant tumors. The present global supply of 225Ac is 1.7 Ci per year yet the global demand is 50-100 Ci. Currently, the production of 225Ac from proton irradiation of 232Th metal targets is being investigated at Brookhaven National Laboratory. One proposed method for separation of 225Ac from bulk thorium targets involves the use of polyoxometalates (POMs), large metal oxide clusters that have been used to chelate high-valent actinides and lanthanides. The modified Wells-Dawson POM ([P2W17O61]10-) has a very high affinity for thorium. Our study seeks to take advantage of the affinity of POMs for thorium to separate 225Acfrom bulk thorium for 225Acproduction. The separation is carried out by adding the POM to aqueous solutions of thorium, lanthanum, and actinium as individual metals and as mixed metal solutions, and contacting those solutions with 3% octylamine in chloroform. The extractions are quantified using ICP-OES. This study has shown that the POM completely extracts the thorium from the aqueous solution and preferentially extracts thorium over lanthanum and actinium.
Thorium-227 (t½:18.7 d) is an alpha emitting nuclide which may also be a candidate for targeted alpha therapy. With its longer half-life, 227Th delivers a lower dose of radiation over time, which may make it a better isotope for treating malignant tumors. Thorium has been found to treat ovarian and bone cancers in mice. In the past 3,4,3-LI(1,2-HOPO) was successfully coordinated to zirconium, found to exhibit high stability in vivoand ultimately built into an 89Zr-based imaging agent. Thorium and zirconium have very similar chemical behavior. Both are +4 oxophilic metals which prefer octadentate ligands. This work investigated the labeling and stability of Th-HOPO in comparison to the standard ligand for labeling, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA). It was found that HOPO had higher yields and higher stability. The development of radiolabeling methods required additional purification of the thorium to separate its many daughter radionuclides. Purification of the thorium was carried out using 8M nitric acid and an anion exchange resin.
Technetium-99 (99Tc, t½: 2.1 x 105years; bmax: 293.7 keV) is a high-yield fission product (6%) in light-water reactors. The removal and permanent storage of technetium from nuclear waste streams is of great importance for the nuclear fuel cycle and for remediation of legacy waste. A fundamental study of the reduction, coordination, and spectroscopic behavior of technetium has been conducted in aqueous and organic media including ionic liquids (ILs). In order to ascertain the value of using ILs in nuclear waste remediation, the behavior of technetium in ILs must be understood. This work sought to understand the behavior of technetium, using electrochemistry and spectroscopy to investigate the behavior of well-known technetium complexes in neat ILs and acid-IL mixtures to probe the effect of ILs on technetium redox chemistry. Titration of bistriflimidic acid (HNTf2) into TcO4-in the IL trimethylbutylammonium bistriflimide (N1114NTf2) showed that the TcO4-anion is protonated in the IL to form HTcO4(pertechnic acid). This protonation was monitored using UV-Vis and x-ray absorption spectroscopy, specifically, EXAFS and XANES, to understand the speciation of TcO4-in this IL. This study has found that technetium is more reactive in ILs.
Hatcher, Jasmine L., "Fundamental Chemistry Related to the Separations and Coordination of Actinium-225, Thorium-227, and Technetium-99" (2018). CUNY Academic Works.