Summary

Lithium is becoming an essential metal due to its application in lithium-ion batteries; however, its recovery from land resources is geographically limited and not environmentally friendly. Harvesting of lithium from natural brine resources is quite common in South America (Europe has very few such natural brine sources), but still occurs with conventional and low-efficiency evaporation processes, while its extraction from minerals, besides pollutant, requires the use of concentrated acidic or alkaline solutions and is energy-intensive. Although there is 231 gigatons of lithium dissolved in seawater, which corresponds to 104 times higher amount than that contained in the land resources, its very low concentration in seawater (less than 0.2 ppm), as well as low efficiency and intermittent nature of possible extraction processes make this option challenging. On the other hand, lithium concentration in brines might be up to 160 times higher than in seawater.

Flow Capacitive Deionization (FCDI) is a new and promising desalination technology (proposed for the first time in 2013) at which flow electrodes (carbon slurries) are used to remove ions from saline water based on the electro-sorption principle. Flow electrodes can be recirculated and regenerated in a loop arrangement between cathode and anode, which allows to increase salts removal and to make the process continuous and energetically efficient. However, several important questions about flow electrode-based systems, including their flow cell design, relatively low conductivity, energy costs associated with regeneration of the carbon particles, and possible clogging during a long-term cell operation remain still unanswered. Moreover, a selective recovery of lithium by FCDI has not been investigated yet. Thus, there is a huge potential for FCDI improvement, for example, by incorporation of ion exchange membranes with functionalised selectivity towards a specific ion. 

Thus, to increase the recovery degree of lithium from saline streams (such as brines and bitterns), and to make the process continuous, we are proposing the incorporation of lithium selective cation exchange composite membranes (which combines polymeric materials with lithium-ion sieves) into a flow-electrode capacitive deionization (FCDI) device.

In this project (Se(L)ect(i)vity), lithium selective composite membranes (Li+SCM) will be developed by electrospinning and modelling tools, such as molecular dynamics simulations, will aid at their design. Long-term validation studies will be performed at the end of the project to examine membranes’ robustness and operational stability.

This work is funded by National Funds through the FCT - Fundação para a Ciência e Tecnologia, I.P., under the scope of the project PTDC/EQU-EQU/6193/2020. This work is also supported by the Associate Laboratory for Green Chemistry – LAQV (https://laqv.requimte.pt/) financed by FCT/MCTES (UIDB/50006/2020). We would also give special acknowledgment to André Batista (Salinas do Samouco - http://www.salinasdosamouco.pt/) for providing samples of bitterns.

Se(L)ect(i)vity team also works at: 1) SEArcularMINE, at which we are developing the first ever 3D printed FCDI device with lithium selective membranes, 2) Flowable Channels, at which we are focusing on the optimization of flow electrode channel geometry based on computational fluid dynamics (CFD) simulations and 3) Digital Twins, which focus on improving and undersatnading membrane processes through CFD simulations.