Optimizations on Lithium ion exchange separation and isotopic measurements

Abstract

Introduction: The Lithium-7 is of interest for nuclear application, being used for primary cooling of PWR (Pressurized Water Reactor) reactors [1]. An environmentally friendly technique is required to replace the Mercury amalgam technique used worldwide [1,2]. This work aims to present the preliminary results of the development of 7Li separation by ion exchange. Methods: A 120 mm x1.0 cm i.d. glass column filled with Dowex 50W-x16 resin was used. A total of 3.0 liters of 0.2 M CH3COOLi solution percolated the column in order to saturate and displace the formed band of 6Li and 7Li. Fractions were collected every 50 mL, then the resin was washed with 5M HNO3 and ultrapure water. The fractions were filtered and evaporated at 80°C, finally taken up with HNO3 1%. Samples were analyzed by ICP-OES – SPECTRO ARCOS. The fractions were analyzed by ICP-MS, model ELAN 6000 – SCIEX. For isotopic ratio measurement, with the parameters of gas flow of approximately 1.1 L min-1, RF 600 W, gas flow rate 1.2 L min-1, Peak Hopping mode, dwell time 80 and 480 for 6Li and 7Li (respectively), 50 sweeps per reading, 1 read per replicate and 10 replicates. Results: A total of 63 samples were collected from the separation experiment. The Li isotopic ratio measured for each fraction was assessed by ANOVA one-way considering the differences among fractions. A statistical significant difference was observed between the fraction 1 and the remainder fractions and the load solution. The remaining fractions showed an isotopic ratio around the natural abundance (6Li/7Li: 7.59%/92.41% = 0.082). The isotopic ratio of this sample indicated enrichment of 7Li of 0.92% in the fraction number 30. Conclusions: The method of ion exchange with Dowex 50W-x16 resin was efficient on 7Li separation and through ICP-MS method was able to measure the δ 84%₀ enrichment of the 7Li. The isotopic separation procedure via ion exchange is still being studied, however the results are promising.