MK-40 Membrane Research Articles

Processing of Sludge Water from Alumina Production by Electrodialysis

The possibility of using the electrodialysis for processing weak aluminate solutions (sludge water) for the purpose of their concentration and causticization is analyzed. For testing, a three-chamber electro-dialysis cell with heterogeneous cation exchange membranes MK-40 was used. The optimal operating parameters of the process were determined, as follows: pole-to-pole distance 3–4 cm and current density 2 A/dm2 at the operating voltage on the cell of 20–26 V. Specific electricity consumption was established as 9.7–20.6 kWh/kg alkali, causticization efficiency 56.1–69.6%, alkali yield – 81%.

Prospects of Processing Tungsten Ores from the Akchatau Deposit

An overview of the composition of wolframite ores of the Akchatau deposit and the technologies for processing concentrates using NaOH and Na2CO3 by hydro- and pyrometallurgical methods is given, and the disadvantages associated with both the technology and the equipment are noted. To develop a technology for processing Akchatau wolframite concentrates, samples of ore materials were taken, the chemical and mineralogical composition of the samples was studied, and enrichment was carried out to obtain rich concentrates. The kinetics of the sintering of the wolframite concentrate with soda was investigated, the dependences of the degree of transformation of the tungsten minerals into sodium tungstate were obtained, and the rate constants, the order of the reaction, and the values of the apparent activation energy were calculated. The results of sintering an enlarged sample of wolframite concentrate with soda in a muffle furnace are presented. After the subsequent leaching, studies were carried out to purify the obtained solutions of sodium tungstate from the impurities while eliminating the operations of the neutralizing solutions through the use of electrodialysis with an MK-40 cation-exchange membrane. The scheme of processing the wolframite ores of Akchatau is proposed.

ELECTROTRANSPOT CHARACTERISTICS OF POLYANILINE-MODIFIED CATION EXCHANGE MEMBRANES IN SOLUTIONS OF NICKEL AND CHROMIUM SULFATES AND SULFURIC ACID

The electrotranspot and structural characteristics of the MK-40 and MF-4SK sulfocationic membranes modified with polyaniline in an electrodialysis apparatus were studied in solutions of nickel and chromium sulfates and sulfuric acid. The decrease in the conductivity of membranes and the increase in their diffusion permeability in solutions of all electrolytes after modification with polyaniline were estimated. The key effect of the charge of the counterion on the electrical conductivity of the initial and modified membranes was confirmed, and an unusual effect of reducing the electrical conductivity of the MF-4SK/PANI membrane with an increase in the concentration of a solution containing multi-charged counter-ion was found. The information on the effect of multi-charged ions on the structure of a homogeneous and heterogeneous membranes, obtained by the method of standard contact porometry, is supplemented by the estimation of transport and structural parameters of microheterogeneous model. Based on the analysis of the parameters of current-voltage curves in solutions of nickel and chromium sulfates and sulfuric acid, the prospects of using the polyaniline-modified membranes in the processes of electrodialysis treatment of acid solutions containing multi-charged ions are evaluated.

Study of the Thermochemical Effect on the Transport and Structural Characteristics of Heterogeneous Ion-Exchange Membranes by Combining the Cell Model and the Fine-Porous Membrane Model.

For the first time, based on the joint application of the fine-porous and cell models, a theoretical analysis of the changing transport and structural characteristics of heterogeneous polymeric ion-exchange membranes (IEMs) MK-40, MA-40, and MA-41 after exposure to elevated temperatures in water and aggressive media (H2SO4 and NaOH solutions), as well as after long-term processing in electrodialyzers of various types, was carried out. The studied membranes are composites of ion-exchange polymers with polyethylene and nylon reinforcing mesh. The external influences provoke the aging of IEMs and the deterioration of their characteristics. The transport properties of IEMs are quantitatively described using five physicochemical parameters: counterion diffusion and equilibrium distribution coefficients in the membrane, characteristic exchange capacity, which depends on the microporosity of ion-exchanger particles, and macroscopic porosity at a known exchange capacity of IEMs. Calculations of the physicochemical parameters of the membranes were performed according to a specially developed fitting technique using the experimental concentration dependences of integral diffusion permeability and specific electrical conductivity, and their model analogs. This made it possible to identify and evaluate changes in the membrane micro- and macrostructure and examine the process of artificial aging of the IEM polymer material due to the abovementioned external impacts.

The Effect of Lactose on the Transport Properties of Ion-Exchange Membranes

The influence of lactose on the basic transport characteristics of ion exchange membranes, including cation-exchange membranes modified by polyaniline, has been studied. A positive effect on biofouling by Bacillus sp. or Shewanella oneidensis MR-1 cell cultures of modified MK-40 and Ralex CMHPES membranes has been found. That is mainly due to the different area of the conductive surface of these membranes. It has been revealed that the presence of lactose in a solution leads to a decrease in the conductivity of all studied membranes. However, the most significant effect is manifested for MK-40 membrane modified by polyaniline: its electrical conductivity is reduced by 15–25%. The diffusion permeability of the anion-exchange and initial cation-exchange membranes is poorly dependent on the presence of lactose in the solution. However, its decrease is observed by 2–2.5 times in the case of cation-exchange membranes modified by polyaniline. A significant effect of lactose on the current-voltage characteristics of the anion-exchange membranes has been found. This fact indicates significant adsorption of lactose on membrane surface in an external electric field. It is shown that ion-exchange membranes remain quite effective for electrodialysis of hydrochloric serum solutions, but their use is more effective at under limiting current modes.

Electrodialysis Separation and Selective Concentration of Sulfuric Acid and Nickel Sulfate Mixed Solution Using Membranes Modified by Polyaniline

The paper discusses the electrodialysis treatment of mixed nickel sulfate and sulfuric acid solution using polyaniline surface-modified cation exchange membranes. The modified membranes are obtained on the basis of industrial cation-exchange MK-40 heterogeneous and MF-4SK homogeneous membranes by in situ oxidative polymerization of aniline under electrodialysis conditions. The conductive and diffusion characteristics of the initial and modified membranes in solutions of sulfuric acid and nickel sulfate are studied. It is shown that the modification of membranes with polyaniline leads to a decrease in their electrical conductivity and diffusion permeability while maintaining high selectivity. The diffusion permeability of cation-exchange membranes is higher in nickel sulfate solutions compared to sulfuric acid one, while an inverse dependence is found for anion-exchange membranes. The competitive transfer of sulfuric acid and nickel sulfate during electrodialysis separation and concentration of their mixture using initial and modified cation-exchange membranes paired with anion-exchange MA-41 membrane are studied. It is shown that the applying a polyaniline layer with positively charged groups on the surface of the MK-40 or MF-4SK cation-exchange membranes suppresses the transport of doubly charged nickel ions both in the separation and concentration modes over the entire range of current densities. The greatest repulsion effect is observed for homogeneous modified membranes, where the selective permeability coefficient P(H2SO4/NiSO4) increases from 0.7–1.7 to 32.5–19.7 depending on the current density. It is established that the use of polyaniline modified cation-exchange membranes permits to concentrate the solution containing 0.1 mol-eq/L (4.9 g/L) H2SO4 and 0.1 mol-eq/L (7.7 g/L) NiSO4, with simultaneous separation into sulfuric acid with concentration about 2.4 mol-eq/L (120 g/L) and nickel sulfate solutions. The content of nickel sulfate in the concentrate does not exceed 0.13 mol-eq/L (10 g/L).

Elecrtochemical Investigation of Heterogeneous Cation-Exchange Membranes Modified by Polyanilin in Solutions of Monovalent and Divalent Cations

A series of composite ion-exchange membranes based on a heterogeneous cation-exchange MK-40 membrane and polyaniline was obtained under the conditions of electrodiffusion of a monomer and an oxidizing agent. The process of polyaniline synthesis on the membrane surface was accompanied by the registration of chronopotentiograms and the pH of the solution leaving the desalination compartment. The initial MK-40 cation-exchange membrane and the composites based on it were studied by voltammetry and chronopotentiometry in NaCl, CaCl2, and MgCl2 solutions in the same electrodialysis flow cell in which the composites were obtained. To calculate the transport numbers of counterions in membranes in CaCl2 and MgCl2 solutions by the chronopotentiometric method, the apparent fraction of the conducting membrane surface in the NaCl solution was calculated based on experimental data on the potentiometric transport numbers of counterions in the membrane. The conditions for the synthesis of polyaniline on the surface of a heterogeneous MK-40 membrane, leading to the preparation of samples with selectivity to singly charged ions, are revealed.

Monoethanolamine (MEA) Degradation: Influence on the Electrodialysis Treatment of MEA-Absorbent.

The thermal-oxidative degradation of aqueous solutions of carbonized monoethanolamine (MEA, 30% wt., 0.25 mol MEA/mol CO2) was studied for 336 h at 120 °C. Based on the change in the color of the solution and the formation of a precipitate, the occurrence of thermal-oxidative degradation of the MEA solution with the formation of destruction products, including insoluble ones, was confirmed. The electrokinetic activity of the resulting degradation products, including insoluble ones, was studied during the electrodialysis purification of an aged MEA solution. To understand the influence of degradation products on the ion-exchange membrane properties, a package of samples of MK-40 and MA-41 ion-exchange membranes was exposed to a degraded MEA solution for 6 months. A comparison of the efficiency of the electrodialysis treatment of a model absorption solution of MEA before and after long-time contact with degraded MEA showed that the depth of desalination was reduced by 34%, while the magnitude of the current in the ED apparatus was reduced by 25%. For the first time, the regeneration of ion-exchange membranes from MEA degradation products was carried out, which made it possible to restore the depth of desalting in the ED process by 90%.

Transport Properties and Structure of Anisotropic Composites Based on Cation Exchange Membranes and Polyaniline

A comprehensive characterization of basic heterogeneous cation-exchange MK-40 and Ralex CMH membranes and composite membranes with polyaniline based on them was performed, including the determination of conductivity and diffusion permeability, measurement of current–voltage curves in solutions of sodium, calcium, magnesium chlorides and hydrochloric acid, distribution curves of water binding energy and effective pore radii, as well as an assessment of the transport-structural parameters of microheterogeneous model. The time of polyaniline synthesis on the surface of cation-exchange membranes by successive diffusion of an oxidizing agent and monomer solution through the membrane into water was determined. Samples with an anisotropic structure and asymmetric electrotransport properties were obtained. Based on the analysis of the electrotransport properties, structure characteristics and model transport-structural parameters of membranes in solutions of singly and doubly charged ions, the obtained materials were defined as promising for use in the processes of electrodialysis desalination of multicomponent solutions.

Influence of Heterogeneous Ion-Exchange Membranes Composition on Their Structure and Transport Properties

The physicochemical properties of experimental heterogeneous MK-40 and MA-41 membranes with different ratios of ion-exchange resin and polyethylene binder in their composition are studied. It is shown that the specific electrical conductivity in 0.01–1 M NaCl solution decreases by more than 3 times for cation-exchange membranes and by 2 times for anion-exchange ones with a decrease in the content of ion-exchange resin in the membranes from 69 to 55%. It has been established that the diffusion permeability of anion-exchange membranes is more sensitive to their composition and naturally increases with an increase in the ion-exchange resin proportion in the composition. Information on the influence of the heterogeneous membrane composition on its structure, obtained by method of standard contact porosimetry, is supplemented by the calculation of transport-structural parameters of the microheterogeneous and extended three-wire models of the ion-exchange membrane.

Current-Voltage and Transport Characteristics of Heterogeneous Ion-Exchange Membranes in Electrodialysis of Solutions Containing a Heterocyclic Amino Acid and a Strong Electrolyte.

The alterations in current-voltage and transport characteristics of highly basic and strongly acidic ion-exchange membranes, during the electrodialysis of solutions containing a heterocyclic amino acid and a strong electrolyte, were studied. An increase in the catalytic activity of the water splitting process at the surface of heterogeneous MK-40 and MA-41 membranes upon prolonged contact with proline and tryptophan solutions was found. A significant effect of electroconvection on the components mass transfer through the cation-exchange membrane in the intensive current mode of electrodialysis was revealed for the solution containing a heterocyclic amino acid along with mineral salt (NaCl). This led to a reduction in the length of the "plateau" of the membrane's current-voltage characteristics, in comparison with the characteristics for an individual sodium chloride solution with the same concentration. The changes in the characteristics of the studied ion-exchange membranes caused by contact with solutions containing heterocyclic amino acids during electrodialysis were reversible when applying electrochemical regeneration (cleaning in place) using the overlimiting current mode, corresponding to the region of facilitated transport for these ampholytes.

Stability of Properties of Layer-by-Layer Coated Membranes under Passage of Electric Current.

Electrodialysis with layer-by-layer coated membranes is a promising method for the separation of monovalent and polyvalent ions. Since the separation selectivity is significantly reduced in the presence of defects in the multilayer system, the stability of the modifiers becomes an important issue. This article reports the i-V curves of layer-by-layer coated membranes based on the heterogeneous MK-40 membrane before and after 50 h long electrodialysis of a solution containing sodium and calcium ions at an underlimiting current density, and the values of concentrations of cations in the desalination chamber during electrodialysis. It is shown that the transport of bivalent ions through the modified membranes is reduced throughout the electrodialysis by about 50%, but the operation results in decreased resistance of the membrane modified with polyethylenimine, which may suggest damage to the modifying layer. Even after electrodialysis, the modified membrane demonstrated experimental limiting current densities higher than that of the substrate, and in case of the membrane modified with polyallylamine, the limiting current density 10% higher than that of the substrate membrane.

Application and Visualization of Fluorescent-Tagged Antiscalants in Electrodialysis Processing of Aqueous Solutions Prone to Gypsum Scale Deposition.

Membrane scaling is a serious problem in electrodialysis. A widely used technique for controlling scale deposition in water treatment technologies is the application of antiscalants (AS). The present study reports on gypsum scale inhibition in electrodialysis cell by the two novel ASs: fluorescent-tagged bisphosphonate 1-hydroxy-7-(6-methoxy-1,3-dioxo-1Hbenzo[de]isoquinolin-2(3H)-yl)heptane-1,1-diyl-bis(phosphonic acid), HEDP-F and fluorescein-tagged polyacrylate, PAA-F2 (molecular mass 4000 Da) monitored by chronopotentiometry and fluorescent microscopy. It was found that cation-exchange membrane MK-40 scaling is sufficiently reduced by both ASs, used in 10−6 mol·dm−3 concentrations. PAA-F2 at these concentrations was found to be more efficient than HEDP-F. At the same time, PAA-F2 reveals gypsum crystals’ habit modification, while HEDP-F does not noticeably affect the crystal form of the deposit. The strong auto-luminescence of MK-40 hampers visualization of both PAA-F2 and HEDP-F on the membrane surface. Nevertheless, PAA-F2 is proved to localize partly on the surface of gypsum crystals as a molecular adsorption layer, and to change their crystal habit. Crystal surface coverage by PAA-F2 appears to be nonuniform. Alternatively, HEDP-F localizes on the surface of a deposit tentatively in the form of [Ca-HEDP-F]. The proposed mechanisms of action are formulated and discussed. The application of antiscalants in electrodialysis for membrane scaling mitigation is demonstrated to be very promising.

Profiled Ion-Exchange Membranes for Reverse and Conventional Electrodialysis.

Profiled ion-exchange membranes are promising for improving the parameters of reverse electrodialysis due to the reduction of pumping power and electrical resistance. The smooth commercial heterogeneous cation-exchange MK-40 and anion-exchange MA-41 membranes were chosen as the initial membranes. Profiled membranes with three different types of surface profiles were obtained by hot pressing the initial membranes. The bilayer membranes were made on the basis of single-layer profiled membranes by casting MF-4SK film on the profiled surfaces. The diffusion permeability of all types of single-layer and bilayer profiled membranes was higher than of the initial ones due to the appearance of large defects on their surface during pressing. The conductivity of the profiled membrane was lower in the diluted solution and higher in the concentrated solution than of the initial one for all samples except for the bilayer anion-exchange membrane. The conductivity of that sample was lower than that of the initial anion-exchange MA-41 membrane over the entire range of studied concentrations. The counter-ion transport numbers for all studied membranes were calculated based on the concentration dependences of conductivity and diffusion permeability of the membrane by the microheterogeneous model. The selectivity of single layer and bilayer profiled membranes became lower after their profiling due to the increase of the solution phases of membranes. The asymmetry of the current-voltage curves for all single-layer and bilayer profiled membranes was found. The application of the single layer and bilayer profiled membranes in reverse electrodialysis did not lead to an increase in power density.

Study of the Electrical Conductivity of Ion-Exchange Resins and Membranes in Equilibrium Solutions of Inorganic Electrolytes.

The study of the electrical conductivity of ion-exchange membranes in equilibrium electrolyte solutions is of great importance for the theory of membrane processes, in particular for practical electrodialysis. The purpose of the work is to determine the electrical conductivity of industrial ion-exchange membranes MK-40 and MA-40, as well as their basis—granules of a bulk layer of industrial ion exchangers KU-2-8 and EDE-10p, by differential and modified contact methods in electrolyte solutions and the development of a new methodology that will give the values that are closest to the true ones; determination of the dependence of electrical membrane conductivity depending on the type of counterion and concentration equilibrium solution and granules of a bulk layer of ion exchangers on the volume fraction of a dry ion exchanger with different degrees of compaction. It is shown that the dependence of the electrical conductivity of diaphragms on the electrolyte concentration, according to theoretical ideas, disappears under compression. It has been experimentally established that the difference method gives lower values of electrical conductivity in the region of low concentrations. The data obtained by the contact method are in good agreement with the results obtained for compressed diaphragms. The membrane conductivity decreases with increasing ion size.

Diffusion and Osmotic Permeability of Ion Exchange Membrane MK-40 Using Sodium Chloride Solution

Cation exchange membrane (MK-40) is a commercial membrane with a fixed group that is an important part of the electrodialysis (ED) process. Sodium chloride (NaCl) diffusion and osmotic permeability for MK-40 was studied. A cell containing two compartments was used to analyse the properties of the MK-40 membrane fixed between them. Furthermore, the influence of temperature, NaCl concentration, and operating time on MK-40 properties was investigated. The results showed that the highest diffusion permeability coefficient of NaCl was 7.37×10-9 (m2/s), and the maximum osmotic permeability coefficient of distilled water was 43.8×10-9 (m2/s) at NaCl solution concentration of 0.1 M and 50oC. Generally, the permeability was constant beyond 60 min of operational time. Additionally, the minimum diffusion permeability coefficients of the MK-40 membrane fell by about 22% over time when the concentration of NaCl solution was 1 M at 25oC. To conclude, membrane properties in the ED process depend on the two electrodes (a cathode and an anode), without the diffusion of salts particles. Meanwhile, the most important properties of cation exchange membranes (CEMs) used in electrodialysis are increased membrane efficiency when water and salts transport decrease through CEMs, which leads to a decrease in energy consumption. Thus, the MK-40 membrane showed a good properties due to its low diffusion permeability for concentrated NaCl solution at elevated temperatures and minimum reduction in diffusion permeability of concentrated NaCl solution over time.

Use of the Microheterogeneous Model to Assess the Applicability of Ion-Exchange Membranes in the Process of Generating Electricity from a Concentration Gradient.

The paper shows the possibility of using a microheterogeneous model to estimate the transport numbers of counterions through ion-exchange membranes. It is possible to calculate the open-circuit potential and power density of the reverse electrodialyzer using the data obtained. Eight samples of heterogeneous ion-exchange membranes were studied, two samples for each of the following types of membranes: Ralex CM, Ralex AMH, MK-40, and MA-41. Samples in each pair differed in the year of production and storage conditions. In the work, these samples were named “batch 1” and “batch 2”. According to the microheterogeneous model, to calculate the transport numbers of counterions, it is necessary to use the concentration dependence of the electrical conductivity and diffusion permeability. The electrolyte used was a sodium chloride solution with a concentration range corresponding to the conditional composition of river water and the salinity of the Black Sea. During the research, it was found that samples of Ralex membranes of different batches have similar characteristics over the entire range of investigated concentrations. The calculated values of the transfer numbers for membranes of different batches differ insignificantly: ±0.01 for Ralex AMH in 1 M NaCl. For MK-40 and MA-41 membranes, a significant scatter of characteristics was found, especially in concentrated solutions. As a result, in 1 M NaCl, the transport numbers differ by ±0.05 for MK-40 and ±0.1 for MA-41. The value of the open circuit potential for the Ralex membrane pair showed that the experimental values of the potential are slightly lower than the theoretical ones. At the same time, the maximum calculated power density is higher than the experimental values. The maximum power density achieved in the experiment on reverse electrodialysis was 0.22 W/m2, which is in good agreement with the known literature data for heterogeneous membranes. The discrepancy between the experimental and theoretical data may be the difference in the characteristics of the membranes used in the reverse electrodialysis process from the tested samples and does not consider the shadow effect of the spacer in the channels of the electrodialyzer.

Using a microheterogeneous model to assess the applicability of ion-exchange membranes in the process of reverse electrodialysis

This paper shows the possibility of using a microheterogeneous model to describe the properties of ion-exchange membranes and calculate the characteristics of a reverse electrodialyzer from the data obtained. We studied the properties of eight samples of heterogeneous cation exchange membranes (two samples of each type of membrane). The samples differed in the year of issue and storage conditions. It is shown that for heterogeneous ion-exchange membranes MK-40 and MA-41, the samples' properties can differ significantly. The counterions transport numbers calculated within the framework of the microheterogeneous model for Ralex membranes differ insignificantly. The counterion transport number in 1 mol/L sodium chloride solution is 0.96 for Ralex CM and 0.98 ± 0.01 for Ralex AMH. For the MK-40 membrane, the transport number in the same solution is 0.94 ± 0.04, and for the MA-41 membrane, it is 0.85 ± 0.1. The possibility of calculating the transport numbers and predicting the open-circuit voltage based on simple physicochemical measurements allows selecting the best membrane pairs for the reverse electrodialysis process. Comparison of the open-circuit potential value calculated using the obtained transfer numbers with experimental data showed that in the case of using Ralex membranes, the difference between the experimental and calculated values is 2%. The calculated value of the open circuit potential was 0.19 V/membrane pair or 1.69 V for the investigated reverse electrodialyzer with nine pair chambers.

Layer-by-Layer Coating of MK-40 Heterogeneous Membrane with Polyelectrolytes Creates Samples with Low Electrical Resistance and Weak Generation of H+ and OH- Ions.

Ion exchange membranes covered with layers of polyelectrolytes of alternating charges are characterized by very high monovalent selectivity. This allows the use of such membranes for electrodialytic fractionation of multicomponent solutions. However, the very existence of the boundary at which differently charged layers come in contact can hinder a membrane’s effectiveness by limiting its ion permeability, raising levels of H+ and OH− ions (thus shifting the pH) and increasing the electrical resistance of the membrane, which leads to increased energy consumption. To test how these properties would be changed, we created cheap layer-by-layer-modified membranes based on the heterogeneous MK-40 membrane, on which we adsorbed layers of polyallylamine and sulfonated polystyrene. We created samples with 3, 4, and 5 layers of polyelectrolytes and characterized them. We showed that the application of layers did not decrease the efficiency of the membrane, since the electrical resistance of the modified samples, which increased after application of the first oppositely charged layer, declined with the application of the following layers and became comparable to that of the substrate, while their limiting current density was higher and the shift of pH of treated solution was low in magnitude and comparable with that of the substrate membrane.

Characteristics of the MK-40 and MA-40 Membranes for Industrial Wastewater Treatment – A Review

Characteristics of the MK-40 and MA-40 Membranes for Industrial Wastewater Treatment – A Review