Ionic Liquids for the Selective Solvent Extraction of Lithium from Aqueous Solutions: A Theoretical Selection Using COSMO-RS

Felipe Olea,Claudio Araya-López,Esteban Quijada-Maldonado,Gastón Merlet,Georgina Díaz,Eduardo Villarroel,Rene Cabezas,Guillermo Durán,Julio Romero

doi:10.3390/min12020190

Abstract

In this study, the theoretical design of ionic liquids (ILs) for predicting selective extraction of lithium from brines has been conducted using COSMO-RS. A theoretical model for the solvent extraction (SX) of the metal species present in brines was established considering extraction stoichiometry, the distribution of the extractants between aqueous and IL phases, and IL dissociation in the aqueous phase. Theoretical results were validated using experimental extraction percentages from previous works. Results indicate that, in general, the theoretical results for lithium extraction follow experimental trends, except from magnesium extraction. Finally, based on the model, an IL was proposed that was based on the phosphonium cation as the extractant, along with the phase modifier tributylphosphate (TBP) in an organic diluent in order to improve selectivity for lithium extraction over sodium. These results provide an insight for the application of ILs in lithium processing, avoiding the long purification times reported in the conventional process.

Highlights

At present, lithium (Li) is one of the most strategic and essential elements for technological development and for achieving CO2 neutrality by 2050
Brine is the principal source of lithium [5], but its extraction and separation are tedious because these processes require a solar evaporation step to concentrate the mineral, which results in long processing times ranging from six to eighteen months
Large quantities of freshwater have to be injected into the lithium wells to pump off the brines, which causes water pollution, affecting the biodiversity of the environment and human health [7], not to mention the fact that water is extremely scarce in places where lithium is found [8]

Summary

Introduction

Lithium (Li) is one of the most strategic and essential elements for technological development and for achieving CO2 neutrality by 2050. This is due to the high charge-to-weight ratio exhibited by this metal in the manufacturing of lithium-ion batteries (Li1−x−yMnxCoyO2), which are used to power smart devices and electric vehicles. The processing of lithium resources presents challenges that have to be solved, and the complexity of extraction and purification of this mineral depends on its source. Brine is the principal source of lithium [5], but its extraction and separation are tedious because these processes require a solar evaporation step to concentrate the mineral, which results in long processing times ranging from six to eighteen months. Large quantities of freshwater have to be injected into the lithium wells to pump off the brines, which causes water pollution, affecting the biodiversity of the environment and human health [7], not to mention the fact that water is extremely scarce in places where lithium is found [8]

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