Monovalent Selective Anion Exchange Membranes Research Articles

Study on lithium extraction from brines based on LiMn2O4/Li1-xMn2O4 by electrochemical method

Lithium rechargeable batteries have been used for lithium extraction in recent years. Here, we report on a highly selective lithium recovery system that consists of a LiMn2O4 positive electrode, a Li1-xMn2O4 negative electrode and a monovalent selective anion-exchange membrane. The effect of potential, temperature and coexisting ions on lithium extraction were investigated in this paper, and the lithium recovery system was applied to extract lithium from brine and concentrated seawater. The extraction capacity of Li+ reached 34.31 mg· (1g LiMn2O4) −1 at 1.2V. With higher reaction rate and lower energy consumption, 25°C (room temperature) was considered as the appropriate temperature. The system still remained high selective for Li+ even in the presence of impurity ions (K+, Na+, Mg2+, Ca2+). With simulated brine and concentrated seawater as source solutions, the concentrations of Na+, Mg2+ and Ca2+ were reduced more than 300, 70 and 100 times, consuming 18–19W h per mole of lithium recovered. And the electrodes still had high separation coefficients of Li+ and Men+ (Na+, Mg2+, Ca2+) after five cycles although a slight drop was existing.

Preparation of a monovalent selective anion exchange membrane through constructing a covalently crosslinked interface by electro-deposition of polyethyleneimine

Surface modification by generating a dense anionic layer on the surface of a substrate membrane is the main method for preparing monovalent selective anion exchange membranes. However, this method has a trade-off between the permselectivity and the stability of the surface layer. To overcome this problem, a simple preparative pathway is devised to covalently immobilize the polyethyleneimine (PEI) onto the surface of an anion exchange membrane (partly quaternized poly (phenylene oxide) (QPPO)). Firstly, a brominated poly (2,6-dimethyl-1, 4-phenylene oxide) (BPPO) based anion membrane was prepared by quaternization. Then, this membrane was modified by electro-deposition of a PEI solution. The composition and structure of the membrane were observed by infrared spectroscopy and scanning electron microscopy. The permselectivity was evaluated by electrodialysis in a Cl-/SO42-system. The experimental results prove that the PEI modification method is an effective, simple, feasible and well-controlled strategy to fabricate mono-valent selective anion membranes.

Electrodialysis potential for fractionation of multicomponent aqueous solutions

The paper aimed at the evaluation of the batch electrodialysis (ED) run in the course of treatment and desalination of various aqueous mixtures containing both mineral (sodium fluoride, sodium chloride) and organic substances (dyes or humic acids). The commercial ED stack (PCCell Bed) equipped with standard anion-exchange and cation-exchange membranes or monovalent selective anion-exchange membranes was used. The ED experiments were performed at a constant current density (1.56 or 1.72 mA/cm 2 ). The mechanism of ion migration as well as membrane deposition for variable solution composition and various membrane types was analyzed The calculated mass balance and electrical energy demand for each ED run were helpful in evaluating the membrane fouling intensity. It was found that the presence of organic substances in the treated solution had a minor impact on energy consumption, but rather strongly affected chloride flux. The extent of organics deposition was significantly lower for monovalent selective anion-exchange membranes than for classic anion-exchange membranes.

Phosphate pre-concentration from municipal wastewater by selectrodialysis: Effect of competing components

The effect of competing ions in wastewater on the phosphate pre-concentrating efficiency by selectrodialysis was demonstrated in this study. Nitrate, bicarbonate and sulphate are three ions frequently present in wastewater. An inhibition of these ions to the phosphate concentrating efficiency was found to occur initially, but if the system runs for a longer time, the effect disappears. In the presence of nitrate, bicarbonate and sulphate, the phosphate concentrating efficiency in the product was significantly reduced from 188% to 78% after 210min, but this could be recovered to 161% after 300min. In addition, when operating selectrodialysis with synthetic municipal wastewater, phosphate was concentrated in the product with a twofold concentration compared to the initial concentration in the wastewater. Scaling on the cation exchange membrane and monovalent selective anion exchange membranes was observed during the selectrodialysis process when carrying out the experiment with synthetic municipal wastewater, but the membranes were almost completely recovered after a simple acid cleaning with 0.1M HCl solution for 1h. The present study indicates that selectrodialysis successfully concentrates phosphate from wastewater in the product stream, which makes a subsequent crystallization process viable to recover phosphate from wastewater.

P-recovery as calcium phosphate from wastewater using an integrated selectrodialysis/crystallization process

Abstract A promising and sustainable renewable source of phosphate was obtained through crystallization of calcium phosphate from wastewater. The aim of the present study was to evaluate the feasibility of an integrated selectrodialysis/crystallization process to recover phosphate, in which selectrodialysis was first used to pre-concentrate the phosphate before crystallization in a pellet reactor. The results of selectrodialysis show that an increase in current density, initial pH of the product, and initial feed concentration of phosphate led to an increase in phosphate concentration in the product. The desalination efficiency from wastewater was 87%, the phosphate concentration in the product can reach 16 mM with a purity of 44%, the current efficiency to transport phosphate and chloride was 26.6% for standard anion exchange membrane and 63% for monovalent selective anion exchange membrane. The optimal operational conditions for phosphate recovery with a pellet reactor were examined by changing the initial concentration, the pH and the superficial velocity. A precipitation efficiency of 82.7% of phosphate was achieved at pH 11, an inlet concentration of phosphates of 2.5 mM, a Ca/P molar ratio of 1.5 and a superficial velocity of 61 m/h. From the results, it can be concluded that the pellet reactor combined with selectrodialysis is an appropriate method to recover phosphate from wastewater as calcium phosphate, which is not only technically but also environmentally feasible, reducing water pollution, preventing eutrophication and yielding valuable and sustainable resources.

Treatment of organic dye solutions by electrodialysis

Laboratory tests were performed to determine the efficiency of dye solution desalination by electrodialysis. The study involved anionic dye and mineral salt recovery by obtaining two streams from a salt and dye mixture - dye-rich solution and salt solution. A standard anion-exchange and cation-exchange membranes or monovalent selective anion-exchange membranes were used in the ED stack. It was found that the separation efficiency was strongly dependent on the dye molecular weight. The best results for standard ion-exchange membranes were achieved for the desalination of Direct Black solution. Furthermore, the obtained results implied that the application of monovalent selective anion-exchange membranes improved the recovery of dye and salt solutions - the dye concentration in the diluate remained constant irrespective of the molecular weight of anionic dyes, whereas the salt recovery remained very high (99.5%).

Modified cation exchange resin applied to demineralisation of a liquid industrial waste. Comparison to a classical treatment and electrodialysis

An experimental study has been made on the separation and recovery of some metals from an effluent waste. Three methods (i.e. classical neutralisation, electrodialysis and ion exchange) were used and compared. Purification efficiency was determined in all cases of treatment. It was found that classical treatment causes formation of a large amount of sludge constituted principally of Al(OH) 3, Fe(OH) 3 and CaSO 4. Ten grams of solid were formed using 1 L of effluent treated. The electrodialysis process was efficient for removal of monovalent anions such as Cl − and NO 3 − from effluent using a monovalent selective anion exchange membrane. Increase of current density causes an increase of efficiency. Finally, a cation exchange resin modified by adsorption of tetrabutylammonium or polyethyleneimine on its surface was used and compared to unmodified resin and the two methods of treatment cited above. Modification of the resin surface allowed separation of species according to their valencies and hydration. Cations with high valencies were fixed on the resin modified by tetrabutylammonium, while transition metals were retained by chelate bonding with polyethyleneimine fixed on resin modified by this polyelectrolyte.

Electrodialysis Field Test for Selective Chloride Removal from the Chemical Recovery Cycle of a Kraft Pulp Mill

Chloride accumulation is a serious issue in the kraft pulping process. Chloride can be selectively removed from dissolved electrostatic precipitator dust (ESP dust) in the kraft chemical recovery cycle by electrodialysis with monovalent-selective anion-exchange membranes. In a pilot-scale field test, this process was investigated (total run time, 750 h). The test was performed at about 3.5% of full scale. The process showed outstanding performance and no significant membrane fouling. In feed-and-bleed operation, chloride removal levels of 94% and 61% were tested. The energy consumption for electrodialysis is low (120 kWh per metric ton of chloride removed at a 63% chloride removal level). The process performed very well even with no feed pretreatment, polarity reversal, or membrane cleaning.

Experience with full-scale electrodialysis for nitrate and hardness removal

In regions with intensive agriculture, nitrate concentrations in ground water frequently exceed the EC-standard for drinking water of 50 mg/l NO 3. As a result, many water works are confronted with the necessity of nitrate removal. In principle, there are biological and chemo-physical technologies available. The separation process by means of electrodialysis shows several advantages such as highly selective desalination, high water recovery, practically no addition of chemicals and the possibility of stop and go operation (covering of peak demands). An additional desired side effect of this process is a reduction in water hardness. The principle of electrodialysis involves the removal of ionic components from aqueous solutions through ion exchange membranes under the driving force of an electric field. The degree of desalination, and hence nitrate and hardness removal, is adjusted by the voltage applied to the membrane cells. The quality of the concentrate is controlled by the amount of dilution water in the concentrate cycle. In 1990, Austrian Energy started pilot tests for nitrate removal by means of electrodialysis at the Kleylehof well in Eastern Austria. These tests were carried out for two years. The average nitrate concentration in the raw water was 80 to 100 mg/l NO 3. The hydraulic capacity of the pilot plant amounted to 1 m 3/h. The aims of the research program were to asses the efficiency of desalination in view of nitrate removal, product quality, water recovery with regard to brine quality, the selection of membranes and long-term experience. Due to the specific requirements, which were best met by the electrodialysis process, Austrian Energy obtained an order for the design and erection of a full-scale plant in 1996. The plant should be suitable for seasonal operation in order to cover peak demands in summer. Two possibilities were planned for the disposal of the produced concentrate. The first involved was discharge into the cocal sewage treatment plant, the second—reuse for irrigation. Therefore, a highly selective nitrate removal process was requested. Because of an increase in the raw water nitrate concentration, the plant had to be designed for a maximum of 160 mg/l NO 3. The nitrate selectivity was enhanced by the use of monovalent selective anion exchange membranes. As opposed to the pilot plant, a new electrodialysis-stack design with a membrane length of 1 m was employed. The ED-unit consists of three parallel membrane stacks with a hydraulic capacity of 48 m 3/h each. Thus the plant can be operated with three hydraulic stages (48, 96 and 144 m 3/h). The plant is fully automated and the different hydraulic stages are started and stopped by means of remote control. Plant start-up took place in August 1997. The nitrate concentration in the raw water at that time was 120 mg/l NO 3. The nitrate removal was adjusted to a product concentration of 40 mg/l NO 3. At maximum desalination performance, a minimum nitrate level of 20 mg/l could be achieved. With a nitrate removal of 66% at a total desalination rate of only 25%, the obtained nitrate selectivity is relatively high. After approximately three months of operation and initial investigations with concentrate degradation in the local sewage treatment plant, the nitrate removal plant was shut down and mothballed during the winter for a restart in May 1998.

Low Effluent Processing in the Pulp and Paper Industry: Electrodialysis for Continuous Selective Chloride Removal

Pollution prevention is currently a major focus of the United States pulp and paper industry. Significant process changes are inevitable to implement low effluent processing. The kraft pulping process is prevalent for the production of wood pulp. About 50 million tons of wood pulp are produced annually in the United States alone using the kraft process. Water consumption is currently roughly between 30 and 200 m3 of water per ton of air dry bleached kraft pulp. In-process recycling of water is now being implemented by many mills to reduce the use of increasingly scarce water resources and to reduce the need for waste-water treatment. Mass balance considerations and industrial experience show that nonprocess elements, which are detrimental to the kraft process, such as chloride and potassium, will quickly build up once water use is significantly reduced. High concentrations of chloride and potassium can cause corrosion and lead to more frequent mill shutdowns due to fouling of heat exchanger surfaces in the kraft recovery furnace. Electrodialysis with monovalent selective anion and cation exchange membranes was explored here to selectively remove chlorine as sodium and potassium chloride from a feed stream with very high ionic strength. Experiments with model solutions and extended tests with the actual pulp mill materials were performed. Very good selectivities and current efficiencies were observed for chloride over sulfate. The outstanding performance of the process with actual mill materials containing organic and inorganic contamination shows great promise for rapid transfer to the pilot scale. This work is an example of the usefulness of membrane separations as a kidney in low effluent industrial processing.