Ion-exchange Membranes Research Articles

On optimizing the experimental setup for estimation of the thermal conductivity of thin films

The aim of this study is to show the optimal arrangement of a measurement system for estimating the thermal conductivity of thin films from temperature profiles. For this purpose, two different experimental setup systems, with square and circular cross sections, were designed to estimate the thermal conductivity of thin films and, in particular, of two ion exchange membranes. Both systems were placed horizontally and vertically in order to evaluate the best orientation to more accurately determine thermal conductivity. A three-dimensional numerical simulation was performed using Comsol Multiphysics to predict the heat flow and temperature gradient and to evaluate the effect of the geometry and the orientation on the contact resistances. Each system was first calibrated without the membrane inside in order to estimate all the necessary thermal properties of the different materials of the model. Next, the membrane was placed inside the model, so that the model now includes the thermal conductivity of the membrane as the only unknown parameter. The numerical results were compared with the various measured temperature profiles to estimate the thermal conductivity. The thermal conductivity values of the well-known Nafion 117 membrane and other thicker membrane were determined. A very good agreement with reliable literature values was obtained. The approach presented here, combining experimental and simulated temperature profiles, may provide the basis for a practical alternative to better estimate the thermal conductivity of thin films.

Heavy Metal Removal from Aqueous Solutions Using a Customized Bipolar Membrane Electrodialysis Process.

Lack of safe water availability and access to clean water cause a higher risk of infectious diseases and other diseases as well. Heavy metals (HMs) are inorganic pollutants that cause severe threats to humans, animals, and the environment. Therefore, an effective HM removal technology is urgently needed. In the present study, a customized bipolar membrane electrodialysis process was used to remove HMs from aqueous solutions. The impacts of the feed ionic strength, applied electrical potential, and the type and concentration of HMs (Cd2+, Co2+, Cr3+, Cu2+, and Ni2+) on the process performance were investigated. The results showed that feed solution pH changes occurred in four stages: it first decreased linearly before stabilizing in the acidic pH range, followed by an increase and stabilization in the basic range of the pH scale. HM speciation in the basic pH range revealed the presence of anionic HM species. The presence of HMs on anion exchange membranes confirmed the contribution of these membranes for HM removal in the base channels of the process. While no clear trend was seen in the ionic strength solution, the maximum HM removal was observed when 1.5 g/L NaCl was used. The initial HM concentration showed a linear increase in HMs removal of up to 30 mg/L. A similar trend was seen with an increase in the applied electrical potential of up to 15 V. In general, the amount of HMs removed increased in the following order: Cd2+ ˃ Ni2+ ˃ Co2+ ˃ Cu2+ ˃ Cr3+. Under some operational conditions, however, the removed amount of Cu2+, Co2+, and Ni2+ was similar. The mass balance and SEM-EDX results revealed that the removed HMs were sorbed onto the membranes. In conclusion, this process efficiently separates HMs from aqueous solutions. It showed the features of diluate pH adjustment, reduction in the overall stack electrical resistance, and contribution of anion exchange membranes in multivalent cation removal. The mechanisms involved in HMs removal were diffusion and migration from the bulk solution, followed by their sorption on both cation and anion exchange membranes.

Continuous iontronic chemotherapy reduces brain tumor growth in embryonic avian in vivo models

Local and long-lasting administration of potent chemotherapeutics is a promising therapeutic intervention to increase the efficiency of chemotherapy of hard-to-treat tumors such as the most lethal brain tumors, glioblastomas (GBM). However, despite high toxicity for GBM cells, potent chemotherapeutics such as gemcitabine (Gem) cannot be widely implemented as they do not efficiently cross the blood brain barrier (BBB). As an alternative method for continuous administration of Gem, we here operate freestanding iontronic pumps – “GemIPs” – equipped with a custom-synthesized ion exchange membrane (IEM) to treat a GBM tumor in an avian embryonic in vivo system. We compare GemIP treatment effects with a topical metronomic treatment and observe that a remarkable growth inhibition was only achieved with steady dosing via GemIPs. Daily topical drug administration (at the maximum dosage that was not lethal for the embryonic host organism) did not decrease tumor sizes, while both treatment regimes caused S-phase cell cycle arrest and apoptosis. We hypothesize that the pharmacodynamic effects generate different intratumoral drug concentration profiles for each technique, which causes this difference in outcome. We created a digital model of the experiment, which proposes a fast decay in the local drug concentration for the topical daily treatment, but a long-lasting high local concentration of Gem close to the tumor area with GemIPs. Continuous chemotherapy with iontronic devices opens new possibilities in cancer treatment: the long-lasting and highly local dosing of clinically available, potent chemotherapeutics to greatly enhance treatment efficiency without systemic side-effects. Significance statementIontronic pumps (GemIPs) provide continuous and localized administration of the chemotherapeutic gemcitabine (Gem) for treating glioblastoma in vivo. By generating high and constant drug concentrations near the vascularized growing tumor, GemIPs offer an efficient and less harmful alternative to systemic administration. Continuous GemIP dosing resulted in remarkable growth inhibition, superior to daily topical Gem application at higher doses. Our digital modelling shows the advantages of iontronic chemotherapy in overcoming limitations of burst release and transient concentration profiles, and providing precise control over dosing profiles and local distribution. This technology holds promise for future implants, could revolutionize treatment strategies, and offers a new platform for studying the influence of timing and dosing dependencies of already-established drugs in the fight against hard-to-treat tumors.

The impact of membrane orientation on ion flux in bipolar membranes

Bipolar membranes (BPMs) are asymmetric, layered ion exchange membranes that are increasingly being explored for use in electrochemical devices. This study aims to investigate the effect that the direction of a diffusive driving force across a salt solution concentration gradient has on the flux through a BPM due to its asymmetric nature. BPMs were fabricated using PiperION poly(aryl piperidinium) A40 as the anion exchange layer (AEL) and Nafion 212 as the cation exchange layer (CEL) with no interfacial junction catalyst. The permeability of sodium chloride through the BPM membranes was measured across a 0.5molL-1 concentration differential for both orientations of the membrane, e.g. AEL facing the 0.5molL-1 NaCl solution versus the CEL facing the 0.5molL-1 NaCl solution. A flux differential of (76.3 ± 4.8)% was measured for the BPM depending on the direction of the driving force. A model based on Fick’s law and the Donnan equilibrium was developed and used to show that the flux differential results from changes in the ionic environment at the AEL–CEL junction due to differences in the ion diffusion coefficients and fixed charge concentrations of the two layers.

Fabrication and application of a continuously regenerated cationic impurity removal device for ion chromatography

A continuously regenerated cationic impurity removal device (CR-CRD) has been fabricated and applied for ion chromatography (IC). The removal of cationic impurities is realized by electrodialytically replacing the cationic impurities with hydronium ions. The device is configured in a sandwich structure and the central eluent channel is respectively isolated from both electrodes by stacked cation exchange membranes and a bipolar membrane (BPM) plus stacked anion exchange membranes. The eluent channel is packed with cation exchange resins in hydronium form and their continuous regeneration can be achieved by electrodialysis. A desirable feature of the device is gas-free, and no degasser is required. It showed sufficient ability to remove cationic impurities, as indicated by > 99.9 % removal of 10 mL of 1 mM LiOH solution injected (∼10 μmol) or continuous removal of 1 mM LiOH solution at the flow rate of 1 mL/min (1 μmol/min). A useful application was for sample pretreatment in nuclear power industry, by eliminating strong matrix interference of the sample containing LiOH (1 mM) and boric acid (2000 mg/L) with trace anion analysis.

Evaluation Study of Ammonium Removal from Groundwater by Electrodialysis: Case Study of Real Groundwater from the City of Kenitra in Morocco.

In this work, we investigated the feasibility of ammonium removal by electrodialysis (ED), a well-known electro-membrane process, based on the selective migration of anions and cations through anion exchange membranes (AEMs) and cation exchange membranes (CEMs). ED experiments are performed using a laboratory pilot. The ion exchange membranes (IEMs) pair used is AXE/CMX, AXE as an AEMs and CMX as a CEMs. The first tests are performed with real groundwater solutions from Kenitra city (Morocco), spiked with an initial concentration of 3 mg/L NH4Cl. The results gave a specific demineralization (SD) to NH4 + ions of 84.60 %; for a demineralization rate (DR) of 80 % and a time of 60 min. The multivariate principal component analysis (PCA) presents a total inertia of 99.23 %, the majority of the variables of which are positively correlated on the C1 axis with a variance of 95.5 % than that of C2 of 3.78 %. The quality of the diluted water determined by the Legrand-Poirier method showed that the water was aggressive and that the addition of 4.54 mg/L Ca2+ was necessary to balance the water and make it fit for human consumption.

An Innovative Concept of Membrane-Free Redox Flow Batteries with Near-Zero Contact Distance Between Electrodes.

Given that the ion-exchange membrane takes up more than 30% of redox flow battery (RFB) cost, considerable cost reduction is anticipated with the membrane-free design. However, eliminating the membrane/separator would expose the membrane-free RFBs to a higher risk of short-circuits, and the dendrite growth may aggravate this issue. The current strategy based on expanding distances between electrodes is proposed to address short-circuit issues. Nevertheless, this approach would decrease the energy efficiency (EE) and could not restrain dendrite growth fundamentally. Herein, an inexpensive and electron-insulating boron nitride nanosheets (BNNSs)-Nylon hybrid interlayer (BN/Nylon) is developed for general membrane-free RFBs to achieve "near-zero distance" contact between electrodes. And the Lewis acid sites (B atoms) in BNNS can interact with the Lewis base anions in electrolytes, enabling a reduced Pb2+concentration gradient. Additionally, the ultrahigh thermal conductivity and mechanical strength of BNNSs promote the uniform plating/stripping process of Pb and PbO2. Compared with conventional soluble lead RFBs, introducing BN/Nylon interlayers boosts EE by ≈38.2% at 25mAcm-2, and extends the cycle life to 100 cycles. This innovative strategy premieres the application of the BN/Nylon interlayer concept, offering a novel perspective for the development of general membrane-free RFBs.

Rational Design Toward Advanced Non-Flow Aqueous Zinc-Bromine Systems Boosted by Alkaline-Neutral Decoupling Electrolytes.

Non-flow aqueous zinc-bromine batteries (AZBBs) are highly attractive owing to their lightweight construction and largely reduced cost compared with the flow ones. Yet, their development is restricted by the sluggish reaction kinetics of Br2/Br-, the shuttle of soluble polybromide species (Brn -, n is odd), and the poor stability of Zn-based anode. Herein, an effective alkaline-neutral electrolyte decoupling system is constructed to mitigate these issues, where nitrogen-doped carbon felt with high catalytic activity to Br2/Br- reaction is developed for cathode, a cost-effective cation exchange membrane (CEM) of polyethersulfone/sulfonated polyether ether ketone (PES/SPEEK-M) that can stop Brn - is used as separator, and glucose that can inhibit dendrites is introduced as anolyte additive. The constructed flowless AZBB mainly consists of two separate redox couples, including Zn/Zn(OH)4 2- in alkaline anolyte and Br2/Br- in neutral media, where non-cations(e.g. OH-, Zn(OH)4 2-, H2O, and Brn -) can be restricted to their respective chamber by the PES/SPEEK-M while cations can pass by. In the optimized system, good electrochemical performance is achieved, mainly including a surprising discharge voltage of 2.01V, a high average Coulombic efficiency of 96.7%, and a good cycling life of ≈1000 cycles without obvious capacity decay at a fixed charge capacity of 2mAhcm-2.

Abstract LB167: Acetalax (Oxyphenisatin acetate, NSC 59687) and bisacodyl (dulcolax) cause oncosis in triple negative breast cancer by poisoning the ion exchange membrane protein TRPM4

Abstract Triple negative breast cancer (TNBC) is generally unresponsive to current therapies, and the development of new anticancer agents is needed. Oxyphenisatin acetate, called Acetalax, which was used as a laxative in the 1950’s, has recently been reported to have anticancer activity in several murine cancer models. In this study we demonstrate that Acetalax and its structural analog laxative analog bisacodyl (Dulcolax) exhibit potent antiproliferative activity in TNBC cell lines. We show that both cause oncosis, a non-apoptotic cell death characterized by cellular and nuclear swelling and cell membrane blebbing that leads to mitochondrial dysfunction and ATP depletion. Acetalax was further shown to enhance immune and inflammatory responses and inhibit protein synthesis. Mechanistically, we provide evidence that TRPM4 (Transient Receptor Potential Melastatin member 4) is poisoned by Acetalax and bisacodyl. By blocking TRPM4, a monovalent cation channel, Acetalax and Bisacodyl cause oncosis, and TNBC cells without endogenous TRPM4 expression as well as TRPM 4 knockout TNBC cells were found to be Acetalax- and Bisacodyl resistant. TRPM4 was also lost in cells with acquired Acetalax resistance. Moreover TRPM4 is rapidly degraded the ubiquitin-proteasome system upon acute exposure to Acetalax and bisacodyl. Together, these results demonstrate that TRPM4 is a previously unknown target of Acetalax and Bisacodyl and that TRPM4 expression in cancer cells is a predictor of Acetalax and Bisacodyl efficacy, and could be used for the clinical development of these drugs as anticancer agents. Citation Format: Makito Mizunuma, Christophe Redon, Liton Saha, Naoko Takebe, Yves G. Pommier. Acetalax (Oxyphenisatin acetate, NSC 59687) and bisacodyl (dulcolax) cause oncosis in triple negative breast cancer by poisoning the ion exchange membrane protein TRPM4 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB167.

Utilizing a Fe3O4 Magnetite Nanoparticle for Anode Modification in a Microbial Desalination Cell to Treat Saltwater.

The microbial desalination cell (MDC) is a bio-electrochemical system that exhibits the ability to oxidize organic compounds, produce energy, and decrease the saline concentrations within the desalination chamber. The selective removal of ions from the desalination chamber is significantly influenced by the anion and cation exchange membranes. In this study, a three-chamber microbial desalination cell was developed to treat seawater using a synthesize Fe3O4 magnetite nanoparticle (MNP)-modified anode. The impact of different performance parameters, such as temperature, pH, and concentrations of NPs, has been investigated in order to assess the performance of three-chamber MDCs in terms of energy recovery and salt removal. The evaluation criteria of the system included multiple factors such as chemical oxygen demand (COD), Coulombic efficiency (CE), desalination efficiency, as well as system aspects including voltage generation and power density. The highest COD% removal efficiency was 74% at 37°C, pH = 7, and 30g/L salt concentration with an optimized NPs concentration of 2.0mg/cm2 impregnated on anode. The maximum Coulombic efficiency was 10.3% with the maximum power density of 4.3W/m3. The effect of the nanoparticle concentration impregnated on the anode was clarified by the primary factor of analysis. This research has revealed consistent patterns in the enhancement of voltage generation, COD, and Coulombic efficiencies when incorporating higher concentrations of nanoparticles on the anode at a certain point.

Electrolytic Regeneration of Spent Caustic Soda from CO2 Capture Systems

The traditional electrochemical caustic soda recovery system uses the generated pH gradient across the ion exchange membrane for the regeneration of spent alkaline absorbent from CO2 capture. This electrochemical CO2 capture system releases the by-products H2 and O2 at the cathode and anode, respectively. Although effective for capturing CO2, the slow kinetics of the oxygen evolution reaction (OER) limit the energy efficiency of this technique. Hence, this study proposed and validated a hybrid electrochemical cell based on the H2-cycling from the cathode to the anode to eliminate the reliance on anodic oxygen generation. The results show that our lab-scale prototype enabled effective spent caustic soda recovery with an electron utilisation efficiency of 90%, and a relative carbonate/bicarbonate diffusional flux of approximately 40%. The system also enabled the regeneration of spent alkaline absorbent with a minimum electrochemical energy input of 0.19 kWh/kg CO2 at a CO2 recovery rate of 0.7 mol/m2/h, accounting for 30% lower energy demand than a control system without H2-recycling, making this technique a promising alternative to the conventional thermal regeneration technology.

Calibration of a sewage sludge anaerobic digestion model with multiple mineral precipitation for two case studies

Including multiple mineral precipitation in anaerobic digestion models is important to accurately assess the quantity of phosphates (PO4-P) in the liquid phase of digested sludge that can be recovered as a fertilizer in struvite precipitation reactors or by emerging processes such as ion exchange membranes. However, the performance of such processes is highly impacted by the presence of potassium (K+) or calcium (Ca2+) ions, which are most often neglected when validating precipitation models. The novelty of this work was to provide a calibration procedure of an anaerobic digestion model with multiple mineral precipitation that can be used for different case studies and do not focus only on PO4-P but also on K+, Ca2+ Mg2+. To draw this calibration procedure, data from two anaerobic digesters located near Lyon (France) and in the Navarra region (Spain), treating sludge with different biodegradability and concentration ranges of phosphorus (P), calcium (Ca), magnesium (Mg), potassium (K) and soluble inorganic carbon (SIC), have been used. This procedure includes the calibration of the inert COD fraction (fXI,COD) and kinetic precipitation constants (Kr) using Bayesian Monte Carlo techniques. However, a unique parameter set for both anaerobic digesters cannot be identified, leading to site-specific parameters for fXI,COD (0.30 and 0.43), Kr,MgCO3 (274 and 0.4), Kr,CaCO3 (21 and 0.12) and Kr,ACP (270 and 58). The calibrated model was able to estimate PO4-P, Ca2+, Mg2+ and K+ concentration in digested sludge with a relative error below 10 %.

Transport and Structural Characteristics of Heterogeneous Ion-Exchange Membranes with Varied Dispersity of the Ion Exchanger

Transport and Structural Characteristics of Heterogeneous Ion-Exchange Membranes with Varied Dispersity of the Ion Exchanger

Metal coordination combining with electrodialysis for one-step separation of valuable metals from spent lithium-ion batteries

Efficient recycling of valuable metals from spent lithium-ion batteries (LIBs) is essential for the circular economy and ecological environment. However, the simultaneous separation and recovery of multiple metal ions face a huge challenge due to their similar physicochemical properties. Herein, we propose metal coordination combing with electrodialysis to achieve one-step separation of lithium, cobalt, and nickel. By regulating the ligands and ligand concentration, the Co2+ selectively coordinates with ligand to form anionic complex, which passes through the home-made anionic polymer inclusion membrane under electric field. Li+ passes through the monovalent cationic exchange membrane, whereas the Ni2+ is retained in the feed solution, thereby achieving the one-step separation of metal ions. When using NH4SCN as ligand, the transport flux of Li+ and Co(SCN)42- reaches around 25.0 µmol m−2 s−1 and 12.7 µmol m−2 s−1, respectively. Meanwhile, the separation efficiency of lithium and cobalt is 80 % and 95 %, respectively at the NH4SCN concentration of 0.1 M and current density of 10 mA/cm2. Additionally, sustainable solar energy is successfully applied to drive the electrodialysis system, and the purity of lithium, cobalt, and nickel is as high as 94.3 %, ∼100 %, and 99.2 %, respectively, demonstrating great potential in decreasing energy consumption. This work which applies metal coordination combining with electrodialysis for one-step separation of lithium, cobalt, and nickel, provides a promising candidate for the recycling of valuable metals from spent LIBs.

Bipolar membrane electrodialysis for nutrient recovery from anaerobic digestion dewatering sidestream

Anaerobic digestion (AD) offers an efficient means for treating sludge generated in wastewater treatment plants (WWTPs), but nutrient-rich AD dewatering sidestream contributes as much as 30 % of the overall nutrient loading of WWTPs. Several electrochemical approaches are being developed as a sidestream treatment strategy to prevent return of nutrients to WWTP headworks and recover them for fertilizer production. One such method is to produce acids and bases, essential chemicals necessary to facilitate nutrient recovery, using bipolar membrane electrodialysis (BMED). In this study we show simultaneous separation of nutrients and production of acid/base streams with an additional consideration for increasing the concentration of ammonium and phosphate in the final product stream by systematically altering compartment flow rates and hence the retention time of each stream. Using a three-compartment BMED system with a synthetic sidestream containing 50 mM NH3-N and 2 mM PO4-P, we achieved up to 80 % ammonia removal (via a cation exchange membrane) and up to 60 % phosphate removal (via an anion exchange membrane) at a productivity of 34.2 L m−2 h−1. Separated ammonia was recovered (>90 %) in a subsequent membrane contactor (MC) that was fed with acid and base streams produced by the BMED unit. A phosphate recovery > 80 % was achieved by chemical precipitation (CP). In a combined BMED-MC-CP process, the concentrated final product contained 333.9 mM NH3-N and 3.1 mM PO4-P with an energy consumption of 8.9 kWh kg−1 N recovered. These results illustrate that the BMED-based treatment train is a promising strategy for nutrient recovery from AD dewatering sidestream.

Modification of cation exchange membranes for enhanced extraction of lithium from magnesium and sodium brine solutions via selective electrodialysis

Selective extraction of Li + ions from highly saline solutions is challenging due to the presence of competing ions like Mg2+ and Na+. This study employed a straightforward interfacial polymerization technique to modify cation exchange membranes (CEM, CR671) to enhance Li+ transport selectivity and capacities. The modification involved a two-layer coating, with polydopamine (PDA) as the initial layer facilitating subsequent coating with polyethyleneimine (PEI). The second layer, comprising PEI and 2-OH-15-crown-5 ether (15CE), created the channels for selective Li transport through crosslinking with 1,3,5-benzenetricarbonyl trichloride. Fourier transform infrared spectroscopy confirmed the presence of 15CE coating on the modified membranes (15CE-PEI-PDA-CR671), while zeta-potential analysis indicated a positive surface charge attributed to PEI to increase the electrostatic repulsion of divalent cations. Electrochemical impedance spectroscopy demonstrated a reduced impedance of 15CE/PEI-PDA-CR671 for Li transport, indicating its high transport potential and selectivity for Li. Bench-scale electrodialysis experiments simulating high Mg2+ and Na + brine conditions demonstrated promising results that 15CE/PEI-PDA-CR671 membrane achieved up to 80% and 90% Li+ recovery efficiency in Mg2+/Li+ and Na+/Li+ mixtures, respectively. The modified membranes exhibited enhanced selectivity, as evidenced by reduced relative transfer numbers (tMg/Li and tNa/Li). Specifically, 15CE/PEI-PDA-CR671 demonstrated significant improvements in Li+ permselectivity and flux compared to CR671 and PEI-PDA-CR671, highlighting its potential for enhancing Li+ recovery effectively from brine water sources.

Energy harvesting from acid mine drainage using a highly proton/ion-selective thin polyamide film

A huge chemical potential difference exists between the acid mine drainage (AMD) and the alkaline neutralization solution, which is wasted in the traditional AMD neutralization process. This study reports, for the first time, the harvest of this chemical potential energy through a controlled neutralization of AMD using H+-conductive films. Polyamide films with controllable thickness achieved much higher H+ conductance than a commercially available cation exchange membrane (CEM). Meanwhile, the optimal polyamide film had an excellent H+/Ca2+ selectivity of 63.7, over two orders of magnitude higher than that of the CEM (0.3). The combined advantages of fast proton transport and high proton/ion selectivity greatly enhanced the power generation of the AMD battery. The power density was 3.1 W m–2, which is over one order of magnitude higher than that of the commercial CEM (0.2 W m–2). Our study provides a new sustainable solution to address the environmental issues of AMD while simultaneously enabling clean energy production.

Advancing Lithium-Magnesium Separation: Pioneering Swelling-Embedded Cation Exchange Membranes Based on Sulfonated Poly(ether ether ketone).

With the continuous advancement of electrodialysis (ED) technology, there arises a demand for improved monovalent cation exchange membranes (CEMs). However, limitations in membrane materials and structures have resulted in the low selectivity of monovalent CEMs, posing challenges in the separation of Li+ and Mg2+. In this investigation, a designed CEM with a swelling-embedded structure was created by integrating a polyelectrolyte containing N-oxide Zwitterion into a sulfonated poly(ether ether ketone) (SPEEK) membrane, leveraging the notable solubility characteristic of SPEEK. The membranes were prepared by using N-oxide zwitterionic polyethylenimine (ZPEI) and 1,3,5-benzenetrlcarbonyl trichloride (TMC). The as-prepared membranes underwent systematic characterization and testing, evaluating their structural, physicochemical, electrochemical, and selective ED properties. During ED, the modified membranes demonstrated notable permeability selectivity for Li+ ions in binary (Li+/Mg2+) systems. Notably, at a constant current density of 2.5 mA cm-2, the modified membrane PEI-TMC/SPEEK exhibited significant permeability selectivity in the Li+/Mg2+ system, while ZPEI-TMC/SPEEK outperformed, displaying remarkable permeability selectivity in the Li+/Mg2+ system, surpassing commercial monovalent cation-selective membrane commercial monovalent cation-selective membrane (CIMS). Furthermore, in the Li+/Mg2+ binary system, Li+ flux reached 9.78 × 10-9 mol cm-2 s-1 for ZPEI-TMC/SPEEK, while its Mg2+ flux only reached 2.7 × 10-9 mol cm-2 s-1, showing potential for lithium-magnesium separation. In addition, ZPEI-TMC/SPEEK was tested for performance and stability at high current densities. This work offers a straightforward preparation process and an innovative structural approach, presenting methodological insights for the advancement of lithium and magnesium separation techniques.

Recovery of sulfuric acid and iron from titanium dioxide waste acid by membrane electrolysis combined with selective electrodialysis

The waste acid generated during the production of titanium dioxide contained a high proportion of ferrous ions. Comprehensive utilization of these waste acid involves the recovery of sulfuric acid and iron. However, traditional methods faced difficulty in attaining the desired outcome. Therefore, this study proposed a treatment process primarily based on membrane electrolysis. Initially, selective electrodialysis was employed to recover sulfuric acid from the waste acid. The effects of initial acid concentration, potential, and operating time on the performance of selective electrodialysis were investigated. Subsequently, a three-chamber membrane electrolysis method was utilized to oxidize Fe2+ to Fe3+ in the anode chamber and generate OH– in the cathode chamber. Both compounds were directed to the precipitation chamber through ion exchange membranes, resulting in the formation of iron hydroxide and the successful recovery of iron. The findings revealed that when the waste acid had a high initial concentration, it was recommended to operate at a higher potential. When treating 18 % of the waste acid, 77.5 % of the sulfuric acid can be recovered while 78 % of the ferrous ions were retained. As the acidity decreased, the potential could be reduced, resulting in a higher recovery rate of sulfuric acid and retention rate of Fe2+. By using a current of 150 mA during membrane electrolysis and maintaining a pH of 2.4 in the precipitation chamber, a purity of 94 % iron hydroxide was achieved. The ion flux of the anion exchange membrane decreased by 19 % after 8 h of electrolysis. This reduction could be mitigated by cleaning the membrane with titanium dioxide waste acid with a pH of 0.4 for 30 min. This study is expected to introduce innovative ideas and methods for the efficient and high-purity recovery of resources from titanium dioxide waste acid.

The effect of electrostatically enhanced adsorption of polylysine on a heterogeneous cation-exchange membrane

Electrostatics influences the interactions between charged biopolymers and ion-exchange membranes. When carrying a charge opposite to that bound in the membrane, the biopolymers readily adsorb on the membrane surface, altering local conditions and, thus, affecting the desalination processes that proceed. To provide a coherent description of the consequences of such adsorption, we experimentally investigate the effects of polylysine as a model cationic polymer on the behavior of a heterogenous cation-exchange membrane. We show that even short exposure to polylysine changes the membrane behavior dramatically. Such a change reflects the influence of the adsorbed polylysine on natural convection, electroconvection, and water splitting. By directly observing the membrane-electrolyte interface, we find polylysine suppresses the beneficial electrical-field-induced convective transport at the membrane-electrolyte interface. Specifically, it diminishes electroconvection dominating at the membrane surface for polylysine-free solutions and attenuates natural convection, dictating the developed flow patterns. At the same time, it provides conditions enhancing a water-splitting reaction, significantly affecting the pH of the solutions adjacent to the membrane. All these effects are dependent on the polylysine concentration. Our study emphasizes the potentially harmful impact of biomolecular adsorption mediated by electrostatic interactions.