Lithium isotope separation by precipitation method coupled with solvent extraction with 1-Hydroxy-4-(p-toluidino) anthraquinone

Abstract

This paper reported a novel chelating agent and a green precipitation-extraction separation strategy for lithium isotope enrichment. 1-Hydroxy-4-(p-toluidino) anthraquinone and anisole were used as chelating agent and diluent, respectively. Three phases including organic phase, aqueous phase and precipitation could be preparated. The experiment indicated that excess sodium hydroxide was helpful to promote the single-stage precipitation rate and equilibrium time. The isotope result indicated that 6Li was concentrated in the aqueous phase and 7Li was concentrated in precipitation phase. The maximum single-stage lithium isotope speration factor reached to 1.013 ± 0.001. By doing thermodynamic analysis of the reaction, the free energy change (ΔG), enthalpy change (ΔH) and entropy change(ΔS) of the separation process were −8.97 J mol−1, −21.37 J mol−1 and −0.0438 J mol−1 K−1 at 283 K. The results of DFT simulation and wave function analysis indicated that a lithium ion combined with a chelating agent anion formed a stable six-member ring between two oxygen, which was more stable than sodium ions combined with chelating agent anions (the Gibbs free energy of the lithium ions reaction was more negative). As interaction analysis result showed, the Li-O bond in complex interaction was significantly stronger than the Li-O bond interaction in aqueous phase, which was the theroy that led to the enrichment of 7Li in organic phase. In the activated carbon treatment experiment, it was found that part of lithium chelator solved in aqueous phase, which resulted in that the lithium abundance of aqueous phase hardly changed. In order to increase the abundance of 6Li in aqueous phase, it is necessary to add adjuvant to reduce the water solubility of lithium chelate. Overall, an economical and environmental-friendly precipitation method with a certain application prospect for lithium isotope separation was proposed, and the direction of improving the separation performance was pointed out in this paper.