Abstract

The isotope separation via liquid-liquid extraction (LLE) using crown-ether (DC18C6) was carried out in order to demonstrate the feasibility of calcium isotope enrichment, which aimed to find a cost-effective way to enrich calcium-48 (⁴⁸Ca) for the study of neutrinoless double beta decay (0vββ) in the CANDLES project. The LLE results revealed that the extraction was solvent dependent in the presence of HCl and the distribution coefficient (D) increased approximately threefold (0.0546±0.0012) with 12 M HCl solvent under a 3.9 M CaCl₂ (aq) (30% w/w) system. Furthermore, the HCl solvent maintained the calcium content attached to the crown-ether at lower feed concentrations. The reaction cell ICP-MS (Agilent 7900) with an additional H2 gas was used to analyze the isotopic composition. The single-stage separation factor of organic phase was found to be 0.992±0.003, 0.994±0.003, 0.996±0.004 for ⁴⁸Ca/⁴²Ca, ⁴⁸Ca/⁴³Ca, and ⁴⁸Ca/⁴⁴Ca, respectively in the extracted organic phase of 3.3 M CaCl₂ (aq) (30% w/w) system. The obtained results were comparable with the HCl solvent system. As a result, without the addition of an acidity reagent, the production of the enriched ⁴⁸Ca isotope via LLE was highly feasible. To improve the mass production of enriched ⁴⁸Ca, filter separation was applied in order to shorten the time required and to study various volumes of the extraction system. The results indicated that the extraction efficiency of filter LLE was comparable to conventional LLE. Filter LLE resulted in more than threefold reduction in time required (approximately 10 minutes for a complete single-stage separation) in comparison with a conventional LLE, consequently implying great potential in the enrichment and mass production via filter LLE.