A calculation model for liquid-liquid extraction of protactinium by 2,6-dimethyl-4-heptanol

Abstract

Reprocessing of spent nuclear fuel usually employs the solvent extraction technique to recover fissile material, isolate other valuable radionuclides, recover precious metals, and remove contaminants. Efficient recovery of these species from highly radioactive solutions requires a detailed understanding of reaction conditions and metal speciation that leads to their isolation in pure forms. Due to the complex nature of these systems, identification of ideal reaction conditions for the efficient extraction of specific metals can be challenging. Thus, the development of experimental approaches that have the potential to reduce the number of experiments required to identify ideal conditions are desirable. In this study, a full-factorial experimental design was used to identify the main effects and variable interactions of three chemical parameters on the extraction of protactinium (Pa). Specifically we investigated the main effects of the anion concentration (NO3-, Cl-) extractant concentration, and solution acidity on the overall extraction of protactinium by 2,6-dimethyl-4-heptanol (diisobutylcarbinol; DIBC) from both HCl and HNO3 solutions. Our results indicate that in HCl, the extraction of protactinium was dominated by the solution acidity, while in nitric acid the extraction was strongly effected by the [DIBC]. Based on our results, a mathematical model was derived, that describes the relationship between concentrations of anions, extractant, and solution acidity and the expected values of Pa distribution coefficients in both HCl and HNO3. This study demonstrates the potential to predict the distribution coefficient values, based upon a mathematical model generated by a full-factorial experimental design.

Partitioning of naturally-occurring radionuclides (NORM) in Marcellus Shale produced fluids influenced by chemical matrix

“…1,5 Sequential extractions were based on previously published methods. 26 In partitioning and sequential extraction experiments, 226 Ra was determined by 222 Rn emanation, 5 203 Pb by NaI gamma spectrometry based on standard laboratory methods, 27 and nat U, nat Th, and 210 Po by preconcentration and alpha spectrometry. 1,28 …”

“…1,5 Sequential extractions were based on previously published methods. 26 In partitioning and sequential extraction experiments, 226 Ra was determined by 222 Rn emanation, 5 203 Pb by NaI gamma spectrometry based on standard laboratory methods, 27 and nat U, nat Th, and 210 Po by preconcentration and alpha spectrometry. 1,28 Grain size Sediment grain-size distribution was analyzed using the pipette method with size fraction breaks at <2 m (clay), 2-20 m (ne silt), 20-50 m (coarse silt) and 50 m-2 mm (sand) at the University of Iowa Quaternary Materials Laboratory.…”

“…LS vials were then counted by a well-type sodium iodide (NaI) detector (Ortec) and gamma-emitting radionuclides were quantitated using standard radioactivity measurement techniques, similarly as described previously. 27 Po was separated and quantitated using standard methods previously described. 1 The radionuclides adsorbed to the sediment were then sequentially extracted based on methods previously described.…”

Radiochemical analysis of protactinium speciation

“…A volume correction was performed during the sample analysis to account for only 4/5 of the solution being measured, as described previously. 118 In acid and salt dependency experiments, the solution activities (a) were used to better reflect the effective concentrations in solution, which can deviate significantly from molar concentrations (M) especially in high concentrations of HCl. The molar activity coefficients were obtained from tabulated values.…”