Highly selective ion separations based on counter-flow electromigration in nanoporous membranes

Recycling Lithium-Ion Batteries-Technologies, Environmental, Human Health, and Economic Issues-Mini-Systematic Literature Review

Global concerns about pollution reduction, associated with the continuous technological development of electronic equipment raises challenge for the future regarding lithium-ion batteries exploitation, use, and recovery through recycling of critical metals. Several human and environmental issues are reported, including related diseases caused by lithium waste. Lithium in Li-ion batteries can be recovered through various methods to prevent environmental contamination, and Li can be reused as a recyclable resource. Classical technologies for recovering lithium from batteries are associated with various environmental issues, so lithium recovery remains challenging. However, the emergence of membrane processes has opened new research directions in lithium recovery, offering hope for more efficient and environmentally friendly solutions. These processes can be integrated into current industrial recycling flows, having a high recovery potential and paving the way for a more sustainable future. A second method, biolexivation, is eco-friendly, but this point illustrates significant drawbacks when used on an industrial scale. We discussed toxicity induced by metals associated with Li to iron-oxidizing bacteria, which needs further study since it causes low recycling efficiency. One major environmental problem is the low efficiency of the recovery of Li from the water cycle, which affects global-scale safety. Still, electromembranes can offer promising solutions in the future, but there is needed to update regulations to actual needs for both producing and recycling LIB.

The Effect of Electrolyte Properties on Ionic Transport through Solid-State Nanopores: Experiment and Simulation

Nanopore membranes enable versatile technologies that are employed in many different applications, ranging from clean energy generation to filtration and sensing. Improving the performance can be achieved by conducting numerical simulations of the system, for example, by studying how the nanopore geometry or surface properties change the ionic transport behavior or fluid dynamics of the system. A widely employed tool for numerical simulations is finite element analysis (FEA) using software, such as COMSOL Multiphysics. We found that the prevalent method of implementing the electrolyte in the FEA can diverge significantly from physically accurate values. It is often assumed that salt molecules fully dissociate, and the effect of the temperature is neglected. Furthermore, values for the diffusion coefficients of the ions, as well as permittivity, density, and viscosity of the fluid, are assumed to be their bulk values at infinite dilution. By performing conductometry experiments with an amorphous SiO2 nanopore membrane with conical pores and simulating the pore system with FEA, it is shown that the common assumptions do not hold for different mono- and divalent chlorides (LiCl, NaCl, KCl, MgCl2, and CaCl2) at concentrations above 100 mM. Instead, a procedure is presented where all parameters are implemented based on the type of salt and concentration. This modification to the common approach improves the accuracy of the numerical simulations and thus provides a more comprehensive insight into ion transport in nanopores that is otherwise lacking.

Enhanced Mono/Divalent Ion Separation via Charged Interlayer Channels in Montmorillonite-Based Membranes

Efficient mono- and divalent ion separation is pivotal for environmental conservation and energy utilization. Two-dimensional (2D) materials featuring interlayer nanochannels exhibit unique water and ion transport properties, rendering them highly suitable for water treatment membranes. In this work, we incorporated polydopamine/polyethylenimine (PDA/PEI) copolymers into 2D montmorillonite (MMT) nanosheet interlayer channels through electrostatic interactions and bioinspired bonding. A modified laminar structure was formed on the substrate surface via a straightforward vacuum filtration. The electrodialysis experiments reveal that these membranes could achieve monovalent permselectivity of 11.06 and Na+ flux of 2.09 × 10-8 mol cm-2 s-1. The enhanced permselectivity results from the synergistic effect of electrostatic and steric hindrance effect. In addition, the interaction between the PDA/PEI copolymer and the MMT nanosheet ensures the long-term operational stability of the membranes. Theoretical simulations reveal that Na+ has a lower migration energy barrier and higher migration rate for the modified MMT-based membrane compared to Mg2+. This work presents a novel approach for the development of monovalent permselective membranes.

Application of Hybrid Electrobaromembrane Process for Selective Recovery of Lithium from Cobalt- and Nickel-Containing Leaching Solutions

New processes for recycling valuable materials from used lithium-ion batteries (LIBs) need to be developed. This is critical to both meeting growing global demand and mitigating the electronic waste crisis. In contrast to the use of reagent-based processes, this work shows the results of testing a hybrid electrobaromembrane (EBM) method for the selective separation of Li⁺ and Co²⁺ ions. Separation is carried out using a track-etched membrane with a pore diameter of 35 nm, which can create conditions for separation if an electric field and an oppositely directed pressure field are applied simultaneously. It is shown that the efficiency of ion separation for a lithium/cobalt pair can be very high due to the possibility of directing the fluxes of separated ions to opposite sides. The flux of lithium through the membrane is about 0.3 mol/(m² × h). The presence of coexisting nickel ions in the feed solution does not affect the flux of lithium. It is shown that the EBM separation conditions can be chosen so that only lithium is extracted from the feed solution, while cobalt and nickel remain in it.

Selective Separation of Singly Charged Chloride and Dihydrogen Phosphate Anions by Electrobaromembrane Method with Nanoporous Membranes

The entrance of even a small amount of phosphorus compounds into natural waters leads to global problems that require the use of modern purification technologies. This paper presents the results of testing a hybrid electrobaromembrane (EBM) method for the selective separation of Cl^- (always present in phosphorus-containing waters) and H₂PO₄^- anions. Separated ions of the same charge sign move in an electric field through the pores of a nanoporous membrane to the corresponding electrode, while a commensurate counter-convective flow in the pores is created by a pressure drop across the membrane. It has been shown that EBM technology provides high fluxes of ions being separated across the membrane as well as a high selectivity coefficient compared to other membrane methods. During the processing of solution containing 0.05 M NaCl and 0.05 M NaH₂PO₄, the flux of phosphates through a track-etched membrane can reach 0.29 mol/(m²×h). Another possibility for separation is the EBM extraction of chlorides from the solution. Its flux can reach 0.40 mol/(m²×h) through the track-etched membrane and 0.33 mol/(m²×h) through a porous aluminum membrane. The separation efficiency can be very high by using both the porous anodic alumina membrane with positive fixed charges and the track-etched membrane with negative fixed charges due to the possibility of directing the fluxes of separated ions in opposite sides.

Ion Separations Based on Spontaneously Arising Streaming Potentials in Rotating Isoporous Membranes

Highly selective ion separations are vital for producing pure salts, and membrane-based separations are promising alternatives to conventional ion-separation techniques. Our previous work demonstrated that simple pressure-driven flow through negatively charged isoporous membranes can separate Li⁺ and K⁺ with selectivities as high as 70 in dilute solutions. The separation mechanism relies on spontaneously arising streaming potentials that induce electromigration, which opposes advection and separates cations based on differences in their electrophoretic mobilities. Although the separation technique is simple, this work shows that high selectivities are possible only with careful consideration of experimental conditions including transmembrane pressure, solution ionic strength, the K⁺/Li⁺ ratio in the feed, and the extent of concentration polarization. Separations conducted with a rotating membrane show Li⁺/K⁺ selectivities as high as 150 with a 1000 rpm membrane rotation rate, but the selectivity decreases to 1.3 at 95 rpm. These results demonstrate the benefits and necessity of quantitative control of concentration polarization in highly selective separations. Increases in solution ionic strength or the K⁺/Li⁺ feed ratio can also decrease selectivities more than an order of magnitude.

Control of Electrolyte Filtration through a Charged Porous Layer (Membrane) Using a Combination of Pressure Drop and an External Electric Field

A novel method is proposed for calculating the solvent flux density and electric current density in the process of flow of an electrolyte solution through a charged porous layer (membrane) under the simultaneous action of external pressure and electric potential gradients. The method is based on irreversible thermodynamics and the cell model of an ion-exchange membrane. It is shown that, with the increase in the electrolyte concentration, the total permeability of the porous structure also increases as a result of both barofiltration and electroosmotic transfer of the solvent when both external gradients are co-directional vectors. As for the current density, it also increases with the increasing electrolyte concentration owing to the growth of the streaming current and specific conductivity.