Measurements and simulations of Li isotope enrichment by diffusion and electrochemical migration using gel-based electrolyte

By Murali, A.; Zhang, Z.; Sarswat, P. K.; Free, M. L.
Published in Separation and Purification Technology 2019

Abstract

Due to the variety of applications of the isotopes in science and engineering as well as their strategic importance in national security, efficient and purity production is essential. 6Li and 7Li have a natural abundance of 7.5% and 92.5%, respectively. Many of the ongoing lithium isotope separation processes have environmental issues, and the use of mercury is one of them and as part of the development of a new lithium isotope separation process, a model based on diffusion and migration processes on the influence of cell lengths and electrode materials, was used to simulate and predict the subtle differences in the concentration and the isotope ratio distribution with time. The three cell lengths used in the model simulation were 2 cm, 5 cm, and 10 cm, all with the two-compartments and two-electrodes configuration to study the influence of cell length on the separation process while the effect of electrode material on 7Li enrichment was investigated using graphite and LiCoO2 coated aluminum foil. The model predicted a higher maximum 6Li/7Li isotope ratio using LiCoO2 coated aluminum electrode and the time it takes for the Li ions to reach the cathode surface increases with the cell length under a second-order polynomial regression. The longer cell of 10 cm gives a better maximum separation factor and a larger volume of higher 6Li/7Li isotope ratio solution at the cost of the time it takes. Experimental tests were conducted in a 2 cm horizontal cell to investigate the influence of electrode materials and also the influence of alternating voltage on the lithium isotope separation. The obtained 7Li/6Li separation factor tests were: 1.010 and 1.008, respectively for the LiCoO2 anode and graphite anode material in the 3-hour long test while the shorter duration tests of 10 and 20 min yielded a high 7Li/6Li separation factor of 1.023 and 1.031, respectively. In addition, multi-stage tests were conducted in a vertical compartment cell for effective 7Li enrichment.

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