Ion Exchange Selectivity Coefficients Research Articles

Sorption of pyridine-3-carboxylic acid and silver(I) from multicomponent aqueous solutions with Dowex-50 sulfonic cation exchange resin

The equilibrium distribution of pyridine-3-carboxylic acid, silver(I) ions, and protons between aqueous solutions and Dowex-50 sulfonic cation exchange resin was studied. The counter-ion composition of the cation exchange resin was determined by solving a system of equations for binary ion exchange selectivity coefficients and the mass balance equation. According to FT IR and CPMAS 13C NMR spectroscopy of solid samples, pyridine-3-carboxylic acid exists in the Dowex-50 phase as [H2L]+ cations. High distribution constants indicate that pyridine-3-carboxylic acid and silver can be concentrated in the polymer phase.

Modified Phillipsite as a Novel Ion-Exchanger for Potassium Extraction from Seawater

Template-free preparation of phillipsite as a novel K+ ion-exchanger was studied systematically by hydrothermal synthesis. The alkalinity, dosage of water glass, dosage of H2O, aging time, reaction temperature and time of hydrothermal synthesis were discussed in detail. The optimized material obtained about phillipsite through the synthesis and testing methods was performed. The K+ ion-exchange capacity and selectivity coefficient were tested. The molar composition for preparing high performance phillipsite obtained was 2K2O:18SiO2:Al2O3:510H2O by optimizing synthetic conditions. The K+ ion-exchange capacity of phillipsite was 57.3 mg/g in seawater. The K+ selectivity coefficient was 88.6 in an equimolar K+ and Na+ mixed solution. Phillipsite can selectively capture K+ over other ions, and therefore can be used for potassium extraction selectively from seawater. Phillipsite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The XRD pattern indicated that the synthetic zeolite was phillipsite. The phillipsite particles exhibited cross-like shape and the average particle size was about 2.5 μm. The synthetic phillipsite was mainly consisted of Si, Al, K and O elements.

Anion recovery from water by cross-linked cationic surfactant nanoparticles across dialysis membranes

Ion exchange selectivity coefficients for a new cross-linked micellar nanoparticle are reported and are used to predict specific ion recovery (e.g., phosphate) across dialysis membranes.

A general framework for ion equilibrium calculations in compacted bentonite

An approach for treating chemical equilibrium between compacted bentonite and aqueous solutions is presented. The treatment is based on conceptualizing bentonite as a homogeneous mixture of water and montmorillonite, and assumes Gibbs–Donnan membrane equilibrium across interfaces to external solutions. An equation for calculating the electrostatic potential difference between bentonite and external solution (Donnan potential) is derived and solved analytically for some simple systems. The solutions are furthermore analyzed in order to illuminate the general mechanisms of ion equilibrium and their relation to measurable quantities. A method is suggested for estimating interlayer activity coefficients based on the notion of an interlayer ionic strength. Using this method, several applications of the framework are presented, giving a set of quantitative predictions which may be relatively simply tested experimentally, e.g.: (1) the relative amount of anions entering the bentonite depends approximately on the square-root of the external concentration for a 1:2 salt (e.g. CaCl2). For a 1:1 salt (e.g. NaCl) the dependence is approximately linear, and for a 1:2 salt (e.g. Na2SO4) the dependence is approximately quadratic. (2) Bentonite contains substantially more nitrate as compared to chloride if equilibrated with the two salt solutions at equal external concentration. (3) Potassium bentonite generally contains more anions as compared to sodium bentonite if equilibrated at the same external concentration. (4) The anion concentration ratio in two bentonite samples of different cations (but with the same density and cation exchange capacity) resembles the ion exchange selectivity coefficient for that specific cation pair.The results show that an adequate treatment of chemical equilibrium between interlayers and bulk solutions are essential when modeling compacted bentonite, and that activity corrections generally are required for relevant ion equilibrium calculations. It is demonstrated that neglecting these aspects may lead to incorrect inferences regarding bentonite structure, and to incorrect interpretation of diffusion data.

Modification of the AMX membrane surface by polyethyleneimine: Effect of ionic strength on the membrane ion exchange selectivity

AbstractIn order to improve the selectivity of the AMX membrane, a polyethyleneimine (PEI) layer was adsorbed on its surface by the immersion of the considered membrane in a solution of PEI. The adsorption process of PEI was studied and the results were well correlated with the Langmuir model and with Lagergren's pseudo‐first‐order kinetic model.Equilibrium ion exchange isotherms of , , and systems, using modified AMX membrane, were established at various ionic strengths from 0.1 to 0.5 mol/L and at constant temperature of 298 K.The results obtained with the modified membrane, in this range of ionic strengths, showed that the affinity order was: at I = 0.1 mol/L and I = 0.2 mol/L and it was for I = 0.3 mol/L and I = 0.5 mol/L. The ion exchange selectivity coefficients , thermodynamic ion exchange equilibrium constants , and the standard free enthalpies of the ion exchange reactions were determined for the three binary systems. These results were compared with those obtained with the unmodified membrane. It was observed that for the modified membrane the ion exchange selectivity towards sulphate ions decreased and increased towards monovalent anions.

Purification of organic acids by chromatography with strong anionic resins: Investigation of uptake mechanisms

Bio-based organic acids are promising renewable carbon sources for the chemical industry. However energy-consuming purification processes are used, like distillation or crystallization, to reach high purities required in some applications. That is why preparative chromatography was studied as an alternative separation technique. In a previous work dealing with the purification of lactic, succinic and citric acids, the Langmuir model was insufficient to explain the elution profiles obtained with a strong anionic resin.Consequently the Langmuir model was coupled with a usual ion-exchange model to take into account the retention of their conjugate bases (<2%), which are commonly neglected at low pH (<1.5). Elution simulations with both uptake mechanisms fitted very well with experimental pulse tests. Only two parameters were optimized (equilibrium constant of acid uptake and ion-exchange selectivity coefficient of conjugate base) and their value were coherent with experimental and resin suppliers’ data.These results confirmed that the singular tailing and apparent delay observed with succinic and citric acids can be explained by the high affinity of succinate and citrate for resin cationic sites. The model was implemented in a preparative chromatography simulation program in order to optimize operating parameters of our pilot-scale ISMB unit (Improved Simulated Moving Bed). The comparison with experimental ISMB profiles was conclusive.

Synthesis and ion exchange properties for Cs+ of ammonium-type mordenite

Cesium content in the seawater is 3.0 × 10−4mg·L-1, and ammonium-type mordenite was used to exchange cesium from cesium source. K-type mordenite was obtained by hydrothermal synthesis method. After ammonium-modified, ion exchange properties such as saturated ion exchange capacities and selectivity coefficients for alkali metal ions were determined. At the same time, ion exchange isothermal curves of ammonium-type mordenite for Cs+ and NH4 + were determined at 25 °C. Pitzer electrolyte solution theory was used to work out activity coefficients of the system, and the Kielland diagram of the ion exchange system was obtained. The calculated equilibrium constant (K a) and ion free enthalpy (ΔG 0) of mordenite for Cs+ and NH4 + are 1.455 and −930.3 J·mol−1, respectively, indicating that ion exchange process of ammonium-type mordenite for cesium is a spontaneous process.

Mineral transformation controls speciation and pore-fluid transmission of contaminants in waste-weathered Hanford sediments

Portions of the Hanford Site (WA, USA) vadose zone were subjected to weathering by caustic solutions during documented releases of high level radioactive waste (containing Sr, Cs and I) from leaking underground storage tanks. Previous studies have shown that waste-sediment interactions can promote variable incorporation of contaminants into neo-formed mineral products (including feldspathoids and zeolites), but processes regulating the subsequent contaminant release from these phases into infiltrating background pore waters remain poorly known. In this paper, reactive transport experiments were conducted with Hanford sediments previously weathered for one year in simulated hyper-alkaline waste solutions containing high or low 88Sr, 127I, and 133Cs concentrations, with or without CO2(aq). These waste-weathered sediments were leached in flow-through column experiments with simulated background pore water (characteristic of meteoric recharge) to measure contaminant release from solids formed during waste-sediment interaction. Contaminant sorption–desorption kinetics and mineral transformation reactions were both monitored using continuous-flow and wet-dry cycling regimes for ca. 300 pore volumes. Less than 20% of contaminant 133Cs and 88Sr mass and less than 40% 127I mass were released over the course of the experiment. To elucidate molecular processes limiting contaminant release, reacted sediments were studied with micro- (TEM and XRD) and molecular- (Sr K-edge EXAFS) scale methods. Contaminant dynamics in column experiments were principally controlled by rapid dissolution of labile solids and competitive exchange reactions. In initially feldspathoidic systems, time-dependent changes in the local zeolitic bonding environment observed with X-ray diffraction and EXAFS are responsible for limiting contaminant release. Linear combination fits and shell-by-shell analysis of Sr K-edge EXAFS data revealed modification in Sr–Si/Al distances within the zeolite cage. Wet-dry cycling did not affect significantly molecular-scale transformations relative to continuous-flow controls. Results indicate that contaminants bound to the solid phase in distinct micro- and molecular-scale coordinative environments can generate similar macro-scale release behaviors, highlighting the need for multi-scale interrogations to constrain mechanisms of reactive transport. Data also indicate that weathering-induced change in ion exchange selectivity coefficients should be incorporated in simulations of contaminant release from caustic high-level radioactive waste impacted sediments.

Effect of major cation water composition on the ion exchange of Np(V) on montmorillonite: NpO2+–Na+–K+–Ca2+–Mg2+ selectivity coefficients

Np(V) sorption was examined in pH 4.5 colloidal suspensions of nominally homoionic montmorillonite (Na-, K-, Ca- and Mg-montmorillonite). Ionic exchange on permanent charge sites was studied as a function of ionic strength (0.1, 0.01 and 0.001M) and background electrolyte (NaCl, KCl, CaCl2 and MgCl2). An ion exchange model was developed using the FIT4FD program, which considered all experimental data simultaneously: Np sorption data, major cation composition of the electrolyte and associated uncertainties. The model was developed to be consistent with the ion exchange selectivity coefficients between the major cations reported in the literature and led to the following recommended selectivity coefficients for Np(V) ion exchange according to the Vanselow convention: logKVNa+NpO2+=-0.20,logKVK+NpO2+=-0.46,logKVCa2+NpO2+=-0.57,logKVMg2+NpO2+=-0.57. Both the experimental data and the estimated selectivity coefficients in this study are consistent with the limited Np(V) ion exchange and sorption data reported in the literature. The results indicate that, as expected, low ionic strengths favor Np(V) sorption when ion exchange is the main sorption mechanism (i.e. acidic to neutral pHs) and that the divalent cations Ca2+ and Mg2+ may be important in limiting Np(V) ionic exchange on montmorillonite.

Sorption of cesium in young till soils

Abstract Soil samples from three forest soil pits were examined down to a depth of approximately three metres using 1 M ammonium acetate extraction and microwave-assisted extraction with concentrated nitric acid (HNO3), to study the binding of cesium (Cs) at Olkiluoto Island, southern Finland. Ammonium acetate was used to extract the readily exchangeable Cs fractions roughly representing the Cs fraction in soil which is available for plants. Microwave-assisted HNO3 extraction dissolves various minerals, e.g. carbonates, most sulphides, arsenides, selenides, phosphates, molybdates, sulphates, iron (Fe) and manganese (Mn) oxides and some silicates (olivine, biotite, zeolite), and reflects the total Cs concentrations. Cs was mostly found in the strongly bound fraction obtained through HNO3 extraction. The average Cs concentrations found in this fraction were 3.53 ± 0.30 mg/kg (d.w.), 3.06 ± 1.86 mg/kg (d.w.) and 1.83 ± 0.42 mg/kg (d.w.) in the three soil pits, respectively. The average exchangeable Cs found in the ammonium acetate extraction in all three sampling pits was 0.015 ± 0.008 mg/kg (d.w.). In addition, Cs concentrations in the soil solution were determined and in situ distribution coefficients (K d) for Cs were calculated. Furthermore, the in situ K d data was compared with the Cs K d data obtained using the model batch experiments. The in situ K d values were observed to fairly well follow the trend of batch sorption data with respect to soil depth, but on average the batch distribution coefficients were almost an order of magnitude higher than the in situ K d data. In situ Cs sorption data could be satisfactory fitted with the Langmuir sorption isotherm, but the Freundlich isotherm failed to fit the data. Finally, distribution coefficients were calculated by an ion exchange approach using soil solution data, the cation exchange capacity (CEC) as well as Cs to sodium (Na) and Cs to potassium (K) ion exchange selectivity coefficients. The calculated distribution coefficients corresponded well with the in situ distribution coefficient values.

Divalent heavy metal selectivity coefficients on kaolinite and bentonite

In order to grasp the adsorptive selectivities of heavy metal ions on the phyllosilicates, the GainsThomas ion exchange selectivity coefficients, K GT of Cd 2+ , Cu 2+ , Pb 2+ and Zn 2+ on Ca-saturated kaolinite and bentonite were determined in comparison with Ca 2+ . Adsorption mechanism was also estimated by the determination in desorption of the ions adsorbed on the phyllosilicates. The average K GT s (min.-max.) on the Ca-kaolinite were 1.0 (0.7-1.3) for Cd 2+ , 1.3 (0.5-2.1) for Cu 2+ , 4.5 (3.3-5.6) for Pb 2+ and 1.3 (0.6-2.1) for Zn 2+ . On the Ca-bentonite, the average K GT s (min.-max.) were 1.0 (0.7-1.9) for Cd 2+ , 1.4 (0.8-2.7) for Cu 2+ , 1.9 (1.5-2.5) for Pb 2+ and 1.7 (1.1-2.7) for Zn 2+ . These results indicated that Cd 2+ has the same adsorptive selectivity onto the surfaces of the phyllosilicates as Ca 2+ . The selectivity of Pb 2+ to kaolinite was found to be specifically higher than those of the other heavy metal ions. It was confirmed that Cu 2+ and Zn 2+ can be adsorbed on the surface of the phyllosilicates with the slightly higher selectivities than the alkaline-earth metal ion. Except for Pb 2+ on kaolinite, most Cd 2+ , Cu 2+ and Zn 2+ (>70%) adsorbed on the phyllosilicates can be desorbed with the 1 mol dm -3 (mol L -1 ) ammonium acetate extraction regardless of clay species and adsorptive equilibrium pH, indicating that many Cd 2+ , Cu 2+ and Zn 2+ are adsorbed on the phyllosilicates in fashion of ion exchange reaction. Half of Pb adsorbed on kaolinite was desorbed with the 1 mol L -1 ammonium acetate extraction and 25% was extracted by 1 mol L -1 HCl, implying the possibility of specific sorption of some Pb 2+ on the phyllosilicate.

Methodology for porting retention prediction data from old to new columns and from conventional-scale to miniaturised ion chromatography systems

Several procedures are available for simulating and optimising separations in ion chromatography (IC), based on the application of retention models to an extensive database of analyte retention times on a wide range of columns. These procedures are subject to errors arising from batch-to-batch variability in the synthesis of stationary phases, or when using a column having a different diameter to that used when the database was acquired originally. Approaches are described in which the retention database can be recalibrated to accommodate changes in the stationary phase (ion-exchange selectivity coefficient and ion-exchange capacity) or in the column diameter which lead to changes in phase ratio. The entire database can be recalibrated for all analytes on a particular column by performing three isocratic separations with two analyte ions. The retention data so obtained are then used to derive a “porting” equation which is employed to generate the required simulated separation. Accurate prediction of retention times is demonstrated for both anions and cations on 2 mm and 0.4 mm diameter columns under elution conditions which consist of up to five sequential isocratic or linear gradient elution steps. The proposed approach gives average errors in retention time prediction of less than 3% and the correlation coefficient was 0.9849 between predicted and observed retention times for 344 data points comprising 33 anionic or cationic analytes, 5 column internal diameters and 8 complex elution profiles.

Lysine Adsorption on Cation Exchange Resin. IV. Temperature Effects on Equilibrium and Kinetics in Batch and Column Systems

Ion exchange equilibria and kinetics are determined for lysine adsorption on the strong acid cation exchanger DIAION SK‐1B at temperatures of 25, 40, and 60°C. The ion exchange equilibrium is found to be independent of temperature. Conversely, the kinetics of ion exchange increases dramatically as the temperature is increased. Average ion exchange selectivity coefficients of 6.0 g/cm3 and 0.52 are obtained for the ion exchange of divalent and monovalent cationic lysine with hydrogen ion, respectively. Resin phase diffusivities are determined by fitting batch binary ion‐exchange data with a mass transfer model based on the Nernst‐Planck equations. As the temperature is increased from 25 to 60°C, the resin phase diffusivity increases from 0.04×10−6 to 0.14×10−6 cm2/s for divalent lysine and from 0.16×10−6 to 0.55×10−6 cm2/s for monovalent lysine. The combination of temperature‐independent ion exchange equilibria and faster mass transfer at higher temperatures results in higher dynamic binding capacity and more efficient desorption of lysine when ion exchange is operated at an elevated temperature. This behavior is confirmed by means of column adsorption/desorption experiments whose results are found to be in agreement with a model incorporating the equilibrium and mass transfer data obtained in this work.

Ion Exchange of H+, Na+, Mg2+, Ca2+, Mn2+, and Ba2+ on Wood Pulp

Ion exchange selectivity coefficients were measured for the partition of metals between solution and pulp fibers. The method accurately models the ion exchange isotherms for all cation pairs evaluated and is accurate up to approximately 0.05 molar concentrations. Selectivity coefficients were determined for calcium and magnesium with each other and with hydrogen, sodium, manganese, and barium. Measurements made at 25°, 50°, and 65°C were used to determine the enthalpy and entropy of the reactions. The data follow the expected linear free‐energy relationship. These results can be used to estimate the ion exchange selectivity coefficients for any temperature within the experimental range.

Role of Ion exchange in permeation processes

The single ion transport of transition metal ions like Cu 2+, Co 2+, Ni 2+ and Zn 2+ were carried out through the H + and alkali metal ion forms of Nafion membrane. These studies showed that the ion exchange selectivity coefficient of the permeating ion had an effect on its transport process. It was found that the diffusion coefficient values ( D) were directly proportional to the selectivity coefficient ( K). This shows that the initial stage of permeation is governed by ion exchange process (effect of K on D).

Preparation and characterisation of dual‐layer latex‐coated columns for open‐tubular capillary electrochromatographic preconcentration of cations combined in‐line with their separation by capillary electrophoresis

A dual-layer ion-exchange latex-coated column was prepared and characterised for on-capillary preconcentration of cations using an open-tubular ion-exchange CEC format. After preconcentration, the analyte cations were eluted with a transient isotachophoretic gradient and separated by CE. The latex double layer was established by first coating the negatively charged wall of the capillary with a layer of cationic quaternary ammonium anion-exchange Dionex AS5A latex particles (60 nm diameter), and then coating a layer of anionic sulphonated cation-exchange Dionex CS3 latex particles (300 nm diameter) onto the underlying AS5A layer. The adhesion of layers is based on electrostatic attractions. Several dual-layer capillaries were characterised for their EOF and ion-exchange capacity and this showed that coatings could be prepared reproducibly by a simple flushing procedure. The dual-layer columns exhibited a moderate, pH-independent EOF (ca. 26 x 10(-9 )m2V(-1)s(-1)) and an ion-exchange capacity of 57 microequiv./g (or 2.69 nequiv./column). Using an 8 cm length of coated capillary combined with a 72 cm length of untreated capillary, a method for on-line preconcentration and separation of monovalent organic bases, alkali metal ions and alkaline earth metal ions by CE was developed. Recoveries for the preconcentration step were 48% for 4-methylbenzylammonium, 43% for benzylammonium, 30-32% for alkali metal ions and 71-75% for alkaline earth cations. In all cases, recoveries were reproducible with RSDs being less than 6.2%. The influences of the ion-exchange selectivity coefficient of the analyte and the sample-loading rate on analyte recovery were also examined. The proposed method was utilised for the determination of alkaline earth cations and low microM detection limits were obtained.

Preparation and characterisation of anion-exchange latex-coated silica monoliths for capillary electrochromatography

Silica monoliths coated with functionalised latex particles have been prepared for use in monolithic ion-exchange capillary electrochromatography (IE-CEC) for the separation of inorganic anions. The ion-exchange monoliths were prepared using 70 nm quaternary ammonium, anion-exchange latex particles, which were bound electrostatically to a monolithic silica skeleton synthesised in a fused silica capillary. The resulting stationary phases were characterised in terms of their chromatographic performance and capacity. The capacity of a 50 μm diameter 25 cm latex-coated silica monolith was found to be 0.342 nanoequivalents and 80,000 theoretical plates per column were typically achieved for weakly retained anions, with lower efficiency being observed for analytes exhibiting strong ion-exchange interaction with the stationary phase. The electroosmotic flow (EOF) was reversed after the latex-coating was applied (−25.96 m 2 V −1 s −1, relative standard deviation (RSD) 2.8%) and resulted in anions being separated in the co-EOF mode. Ion-exchange interactions between the analytes and the stationary phase were manipulated by varying the ion-exchange selectivity coefficient and the concentration of a competing ion (phosphate or perchlorate) present in the electrolyte. Large concentrations of competing ion (greater than 1 M phosphate or 200 mM perchlorate) were required to completely suppress ion-exchange interactions, which highlighted the significant retention effects that could be achieved using monolithic columns compared to open tubular columns, without the problems associated with particle-packed columns. The latex-coated silica monoliths were easily produced in bulk quantities and performed reproducibly in acidic electrolytes. The high permeability and beneficial phase ratio makes these columns ideal for micro-LC and preconcentration applications.

CA2+-FE2+ AND CA2+-MN2+ EXCHANGE SELECTIVITY OF KAOLINITE, MONTMORILLONITE, AND ILLITE

The Gains-Thomas ion exchange selectivity coefficients, KGT of Fe2+ and Mn2+ on three types of Ca2+-saturated clay minerals (kaolinite, montmorillonite, and illite) were determined in an oxygen-free condition in order to understand better the behaviors of these ions in anaerobic soils. The average ion exchange selectivity coefficients:KGT of Fe2+ to Ca-kaolinite was 1.13, with a variation of 0.72–1.46, regardless of the charge fractions of Fe2+ adsorbed on the surface sites (EFe), indicating that the selectivity of Fe2+ to the surface of kaolinite was similar to that of Ca2+. The KGT values of Fe2+ to Ca-montmorillonite were high at low EFe and shifted to near 1.0 with an increase of EFe. In contrast, the KGT values of Fe2+ to Ca-illite were apparently high, near 40, at low EFe and decreased to a range of 2 to 3 with an increase of EFe, being markedly higher than those for kaolinite and montmorillonite. For both Ca-kaolinite and Ca-montmorillonite, the selectivity coefficients KGT values of Mn2+ were constant, near 1.0 with a variation of 0.66–1.51, regardless of EMn. The KGT values of Mn2+ in Ca-illite were approximated 1.4 with a range of 0.52 – 2.41. These results suggest that the solution systems composed of Mn-clay minerals and Ca-clay minerals can be regarded as thermodynamically ideal behavior. This confirms that Mn2+ can be adsorbed uniformly on the surface of the clay minerals with selectivity similar to that of alkaline-earth ions.

Lysine Adsorption on Cation Exchange Resin. I. Ion Exchange Equilibrium and Kinetics

Ion exchange equilibria and kinetics are determined for lysine adsorption on the strong acid cation exchanger Dowex HCR‐W2. Average ion exchange selectivity coefficients of 5.0 g/cm3 and 0.75 are obtained for the ion exchange of divalent and monovalent cationic lysine with hydrogen ion, respectively, while values of 1.5 and 1.9 are obtained for the exchange of ammonium and potassium with hydrogen ion. A model based on these binary ion exchange measurements and accounting for the solution equilibria is then developed to predict lysine adsorption over a broad range of conditions. Similarly, resin phase diffusivities are determined by fitting batch binary ion‐exchange data with a mass transfer model based on the Nernst‐Planck equations. Diffusivities of divalent cationic lysine, monovalent cationic lysine, ammonium ion, and potassium ion are 0.05 × 10−6, 0.20 × 10−6, 1.6 × 10−6, and 1.9 × 10−6 cm2/s, respectively. Finally, a general rate model incorporating ion exchange and solution equilibria is developed to predict batch adsorption and desorption of lysine using these diffusivity values over a broad range of conditions.

Bi-ionic chloride-nitrate equilibrium in a commercial ion-exchange membrane

Chloride-nitrate equilibrium was studied using the Neosepta ACS® anion-exchange membrane. Ion-exchange isotherm and selectivity coefficient were performed on the basis ofthe Donnan equilibrium and Helfferich's equilibrium relationship. Fixed ionic group concentration and water activity coefficients in the membrane were constant for any concentration of the nitrate and chloride ions in the solution. It was shown that the selectivity coefficient is more than unity and that the membrane has a good selectivity for nitrate ions.