Radionuclide extraction

Currently, the situation seems promising for the study of new solvents for common radionuclide extraction. However, to date, only empirical investigation has been performed. The problem of gaining a quantitative description of coextractant influence on one another has practically not been investigated. But the attractive target, to create a simple and cost-effective flowsheet for HLW processing, is the serious reason to continue the efforts in this direction. 

After both sets of experiments were completed, the ground-water was drained from the cells and selective chemical extractions of the granite cell walls were performed. The cells were filled with 0.5 mol/L CaCl solution and stirred continuously for 72 h to displace exchangeable radionuclides. After a rinse with demineralized water to remove residual CaCl- solution, the cells were filled with KTOX solution and stirred ror 24 h to remove radionuclides associated with oxyhydroxides. All solutions were analyzed by gamma spectrometry to determine the amounts of radionuclides extracted. Residual activity was measured by direct gamma counting of the cells. 

On the other hand, there are some ionization techniques that are very useful, particularly at very high mass, but produce ions only in pulses. For these sources, the ion extraction field can be left on continuously. Two prominent examples are Californium radionuclide and laser desorption ionization. In the former, nuclear disintegration occurs within a very short time frame to give a... 

Crown ethers as analytical reagents and extractants of radionuclides 98MI36. 

Cyclotrons and accelerators are sources of charged particles (i.e., protons, deuterons, a particles, etc.), and the radionuclides produced are generally proton rich and decay by positron emission and/or electron capture. A positive ion beam is eventually extracted from the cyclotron, regardless of whether positive or negative ions were accelerated. The isotope of interest is separated from the target for use in chemical syntheses. Accelerator- or cyclotron-produced radioisotopes tend to be the most expensive as only one radionuclide is produced at a time. 

Recent years have also seen the development of a variety of com-plexation reagents incorporating C-P bonds and their associated functionalities, such as phosphoryl linkages. For example, substituted calixarenes (Figure 1.4) have been developed for extraction of radionuclides, and phosphorus-derivatized cyclodextrins for stereospecific inclusion interactions. 

The centrifugal separator of the AKUEVE system is also used for phase separation in the SISAK technique [84]. SISAK is a multistage solvent extraction system that is used for studies of properties of short-lived radionuclides, e.g., the chemical properties of the heaviest elements, and solvent extraction behavior of compounds with exotic chemical states. In a typical SISAK experiment, Fig. 4.34, radionuclides are continuously transported from a production... 

Solvent extraction techniques are frequently used to identify and characterize products of nuclear reactions, because the elemental (M) distribution ratios (Dm) that provide the scientific information can be measured at extremely low metal concentrations, as described in Chapter 4, providing information about the chemical properties of the metal ion. Figure 12.17 illustrates an example of such studies. Sophisticated radiometric analytical techniques greatly facilitate measurement of distribution ratios of radionuclides at very low concentrations. 

T0005 Active Environmental Technologies, Inc., TechXtract T0066 Argonne National Laboratoiy, Transuranium Extraction (TRUEX) Process T0132 Brookhaven National Laboratory, Biochemical Recovery of Radionuclides and Heavy Metals... 

High concentration of nontargeted ionic contaminants may reduce the efficiency of the 3M Empore extraction disk. Due to the high loading capabilities of the Empore membranes, the radionuclide concentration on the filters must be monitored to ensure that the membranes do not exceed the limits for low-level radioactive waste. 

TechXtract is an extraction technology that has been used to remove a variety of contaminants from the surfaces of concrete, steel, brick, and other materials. Target contaminant types include organics, heavy metals, radionuclides, and polychlorinated biphenyls (PCBs). The technology uses proprietary chemical formulations in successive steps to remove these contaminants. The process employs as many as 25 different components in 3 separate chemical formulations that are applied to the contaminated surface and then removed in a multi-step, multicycle sequence. TechXtract is commercially available and has been used at multiple sites. 

ANL claims the technology is promising because radionuclides are separated from waste streams by a simple, compact, cost-effective process that does not produce large secondary waste streams. The MACS process is intended to reduce the complexity of equipment when compared to solvent extraction and ion exchange techniques, and to facilitate scale-up due to the systems inherent simplicity. 

Brookhaven National Laboratory s (BNL s) biochemical recovery of radionuclides and heavy metals is a patented biochemical recovery process for the removal of metals and radionuclides from contaminated minerals, soil, and waste sites. In this process, citric acid, a naturally occurring organic complexing agent, is used to extract metals and radionuclides from solid wastes by the formation of water-soluble, metal-citrate complexes. The complex-rich extract is then subjected to microbiological biodegradation that removes most of the extracted heavy metals. 

Researchers at BNL claim that this technology may be used to extract metals such as cadmium, arsenic, lead, zinc, copper, magnesium, manganese, aluminum, barium, nickel, and chromium, as well as radionuclides such as uranium, thorium, plutonium, cobalt, cesium, and strontium. They state that the process offers the following advantages ... 

The vendors state that data from bench- and pilot-scale evaluations of Diphonix resin should only be used as a general guide to applications of the technology to real-world applications. Each use of the technology will likely require site- and waste-specific evaluations before the initiation of treatment. Some metals (i.e., iron and aluminum) can interfere with the extraction of targeted radionuclides in mixed-waste applications. 

The lonsiv ion exchange resins are extraction technologies used to separate radionuclides from alkaline wastewater in the presence of competing cations. These resins include lonsiv IE-910 and lonsiv IE-911, which are manufactured using a new class of crystalline silicotitanates (CSTs) invented by researchers from Sandia National Laboratory (SNL) and Texas A M University. CSTs demonstrate high distribution coefficients in acidic, neutral, and alkaline solutions with high concentrations of competitive ions such as sodium and potassium. The affinity of CSTs for strontium in neutral or alkaline wastes is also high. 

UOP molecular sieves (UOP) has developed the lonsiv family of ion exchange resins for the extraction of radionuclides from wastewater. lonsiv TIE-96 is composed of a titanium-coated zeolite (Ti-zeolite) and is used to separate plutonium, strontium, and cesium from alkaline supernatant and sludge wash solutions. The technology was developed by Pacific Northwest Laboratory (PNL) for use at the West Valley, New York, nuclear waste facility. The technology is commercially available. 

Fig. 8. Radionuclide migration studied in a granitic shear zone at the Grimsel test site, Switzerland (injection flow rate 10 mL/min extraction flow rate 150 mL/min, dipole distance 2.3 m). Am(III), Pu(IV) and Th(IV) are co-eluted with the colloids grey vertical lines indicate maxima of breakthrough curves (Geckeis et al. 2003). In order to allow a direct comparison of breakthrough curves, the colloid and radionuclide concentrations (c in mg/mL) in the extracted water samples are normalized to the total injected mass of individual colloid or radionuclide tracers (mn in mg).

The chemical compositions of individual chondrules have been determined by neutron activation of extracted samples or by electron microprobe analyses of chondrules in situ. Some, but not all chondrules are depleted in moderately volatile elements. There is a compositional continuum between the olivine-rich and aluminum-rich chondrules. Original concentrations of the short-lived radionuclide 26A1 in chondrules suggest they formed very early, before all of this isotope decayed, but as much as 2-5 million years after the formation of CAIs (see Refractory Inclusions, below). 

---