Multi-ionic Solutions Research Articles

Simultaneous potentiometric determination of cations and anions in multiionic solutions using PD-sensors based on MF-4SC and Nafion membranes nanomodified with zirconia and silica

The sensitivity of potentiometric PD-sensors (sensors whose analytical signal is the Donnan potential) based on gradient-modified MF-4SC and Nafion membranes to K+, NH4+, CH3COCOO−, HS−, and OH− ions simultaneously present in aqueous solutions has been studied. Hydrated silica and zirconia were used as the dopants. For the simultaneous determination of K+ and NH4+ cations and CH3COCOO− and HS− anions in alkaline solutions, pairs of cross-sensitive PD-sensors with membranes modified with various dopant concentrations have been used, one of which provides the lowest sensitivity and the other the highest sensitivity of sensor to anions. The best repeatability and reproducibility of the results of determining ion concentrations have been obtained when PD-sensors based on the Nafion membranes doped with ZrO2 where used, which can be explained by the denser and more uniform structure of these membranes when compared to MF-4SC.

3D Computational Simulation of Calcium Leaching in Cement Matrices

Calcium leaching is a degradation process consisting in the progressive dissolution of the paste by the migration of calcium atoms to the aggressive solution. It is therefore, a complex phenomenon involving simultaneously several crystalline phases and dissolution and diffusion processes. During this work a new program for the simulation of the degradation process in three dimensions was developed. The program decouples the transport and chemical reaction equations and solves them separately. Transport equations are solved by the Finite Element Method using an algorithm that enables the description of multi-ionic solutions on arbitrary domains. The chemical algorithm accounts for the degradation of portlandite and the CSH gel which are the main constituents of ordinary Portland cement matrices. The program was used to simulate accelerated calcium leaching by a 6M ammonium nitrate solution, in order to test it. The obtained output was a three dimensional representation of the matrix and the values calcium concentration of each particular pixel of the structure at different time steps. This not only makes possible to study the calcium to silicon ratio, porosity and elastic properties of each particular phase as a function of time but also as a function of the position within the matrix.

Biosorption of trace elements from aqueous systems in gold mining sites by the filamentous green algae (Oedogonium sp.)

Metal binding by algae has enormous potential for environmental bioremediation of industrial and urban wastewater. Algae have been proven to be cheaper and more effective for the removal of metallic elements in aqueous solutions. The present work reports the use of dried filamentous green algae, Oedogonium sp., for the sorption of Cu, Co, Cr, Fe, Hg, Ni, Zn and U in single and multi-ion solutions. Algal biomass from a gold mining site in Johannesburg was used in the study. The FT-IR analysis of the biomass revealed the presence of amino, carboxyl, phosphate and carbonyl functional groups. The maximum adsorption capacity was observed between pH2 and 5 for Cr, Cu, Ni and Zn in single-ion solutions, whereas, in multi-ion solutions, the adsorption capacity was constant for the metals studied over the pH regime from 2 to 7, except for Ni and U. The formation of the negatively charged complexes leads to the decrease of the uptake of U beyond pH4. The equilibrium data demonstrated a good fit with the Freundlich model for both cases.The biosorption of metals on the Oedogonium sp. biomass was exothermic and spontaneous and occurred on heterogeneous surface. The Oedogonium sp. biomasses could be repeatedly used up to 3cycles with a virtual increase of their initial adsorption capacity. More than 110% of the metals adsorbed were eluted from the biomass. These results indicate that there were metals initially adsorbed on the biomass which were also released during desorption.Thus, this study demonstrated that algal biomass could be used as an efficient biosorbent for the treatment of trace element-bearing wastewater.

A catechol-like phenolic ligand-functionalized hydrothermal carbon: One-pot synthesis, characterization and sorption behavior toward uranium

We proposed a new approach for preparing an efficient uranium-selective solid phase extractant (HTC-btg) by choosing bayberry tannin as the main building block and especially glyoxal as crosslinking agent via a simple, economic, and green one-pot hydrothermal synthesis. The results of characterization and analysis show that after addition of glyoxal into only bayberry tannin-based hydrothermal reaction system, the as-synthesized HTC-btg displayed higher thermal stability, larger specific surface area and more than doubled surface phenolic hydroxyl groups. The sorption behavior of the sorbents toward uranium under various conditions was investigated in detail and the results indicated that the process is fast, endothermic, spontaneous, and pseudo-second-order chemisorption. The U(VI) sorption capacity reached up to 307.3mgg−1 under the current experimental conditions. The selective sorption in a specially designed multi-ion solution containing 12 co-existing cations over the range of pH 1.0–4.5 shown that the amount of uranium sorbed accounts for about 53% of the total sorption amount at pH 4.5 and distinctively about 85%, unreported so far to our knowledge, at pH 2.0. Finally, a possible mechanism involving interaction between uranyl ions and phenolic hydroxyl groups on HTC-btg was proposed.

Simple small molecule carbon source strategy for synthesis of functional hydrothermal carbon: preparation of highly efficient uranium selective solid phase extractant

In this paper, simple small molecules, glyoxal and acrylonitrile, are chosen as starting materials to prepare an amidoxime-functionalized hydrothermal carbon-based solid phase extractant (HTC-AO) via a one-step hydrothermal process following a simple oximation. The resulting HTC-AO exhibits the anticipated properties, i.e., low porosity (0.01 cm3 g−1) and intraparticle diffusion coefficient (kint = 0.042 mmol g−1 min−0.5), high content of amidoxime groups (1.66 mmol g−1) and minimal undesired functional groups (typically carboxylic group: 0.07 mmol g−1; phenolic group: 0.38 mmol g−1; lactonic group: 0.01 mmol g−1). Moreover, the results of irradiation experiments under γ-ray dosages between 1 and 100 kGy indicate that HTC-AO has good radiation stability. The sorption behavior of U(VI) onto HTC-AO is investigated in detail using batch sorption experiments. A saturation U(VI) sorption capacity over that of all the uranium sorbents reported previously is found to be 1021.6 mg g−1 at pH 4.5 in single uranium solution, and a so far unreported highest uranium selectivity of 81.6% with a sorption capacity of 268.9 mg g−1 is observed at pH 2.5 in multi-ion solution. The significant outcomes in this work confirms that the “simple small molecule carbon source” strategy is practical and efficient, and may have the potential for the preparation of other types of functional materials such as highly specific catalysts, drug targeting carriers and others.

Solution-Diffusion–Electro-Migration model and its uses for analysis of nanofiltration, pressure-retarded osmosis and forward osmosis in multi-ionic solutions

This work presents an analytical solution to the differential equations that govern the electrically coupled transport of three different ions through membrane barrier layers in which the Solution-Diffusion–Electro-Migration model applies. This model disregards convective coupling between the trans-membrane flows of ions and solvent and uses composition-independent single-ion permeances to quantify ion transfer through the membrane. The limited number of adjustable parameters should make their unambiguous determination feasible from a limited set of experimental data. The solution presented here enables rapid calculations that explore the effects of spontaneously arising electric fields on rejections in nanofiltration (NF), volume flows in pressure-retarded osmosis (PRO) through NF membranes, and NaCl rejections in forward osmosis (FO). For NF, ion flux simulations confirm that large differences in the permeances of mono and divalent ions, e.g. Mg2+ and Cl− or Na+ and SO42−, can lead to negative rejections or enhanced rejections of trace monovalent ions, depending on the ion charge. Calculations also show that rejection of divalent ions by NF membranes can lead to significant osmotic flow, even in the presence of some excess of NaCl. Osmotic flow first decreases and then increases as the NaCl concentration increases in a draw solution containing MgCl2 or Na2SO4. In FO using MgCl2 as a draw solution and NF membranes, modeling reveals 3- to 4-fold enhancements in NaCl rejection relative to a pressure-driven process under similar conditions. These results demonstrate the importance of modeling coupled ion transport when designing membrane-based ion separations.

A comparative study of electrosorption selectivity of ions by activated carbon electrodes in capacitive deionization

This study has been focused on an experimental investigation of the electrosorption selectivity for alkali- and alkaline-earth cations in activated carbon-based capacitive deionization process. Cyclic voltammetry experiments showed that a large proportion of micropores in activated carbon electrodes were associated with electrical double-layer overlapping, and the specific capacitance of cations increased with the decrease of hydrated radius. A series of electrosorption experiments were conducted to identify the preferential electrosorption in multi-ionic solutions. The electrosorption selectivity of cations can be determined by the ionic charge, hydrated radius, and initial molar concentration. The activated carbon electrodes presented greater selectivity of smaller ions over larger ions due to size-affinity, while divalent cations possessing higher valence to screen the surface charge were more effectively removed than monovalent cations. The increase of initial molar concentration resulted in the increase of electrosorption capacity. Moreover, the ion selectivity can be further enhanced by increasing the applied voltage. The results are relevant to water desalination and softening in electrosorption.

Concentration polarization phenomenon during the nanofiltration of multi-ionic solutions: Influence of the filtrated solution and operating conditions

One of the major difficulties for the prediction of separation performances in the case of multi-ionic mixtures nanofiltration lies in the description of the concentration polarization phenomenon. Usual models available in literature do not take account of the polarization phenomenon or only describe it cursorily. Very few studies dedicated to the understanding and the specific description of the concentration polarization phenomenon are available in literature and a 2-D multi-ionic model describing the layer heterogeneity along the membrane length has never been proposed yet. The model used in the present work, called Pore and Polarization Transport Model (PPTM), allows an accurate description of the concentration polarization layer occurring during the filtration of multi-ionic solutions by taking account of the radial electromigrative transport in the layer, the turbulence, as well as the axial heterogeneity.In this context, the present paper aims at proposing a numerical investigation of the influence of operating conditions on the behavior of the polarization layer occurring at the membrane vicinity. The input parameters governing the transport through the membrane have been assessed in a previous study in the same experimental conditions so that only the polarization layer is investigated here. The proposed model which was previously validated on experimental observed rejection curves is then used to understand how operating conditions, such as applied pressure, feed flow-rate, or divalent ion proportion, govern the polarization phenomenon. For this purpose, concentration and thickness axial profiles along the membrane length and radial profiles within the polarization layer are investigated for various conditions. Finally, the impact of the type of divalent ion and the number of ions is also studied on various mixtures.

Facile preparation of polyphenolic hydroxyl functionalized uranium-selective chelating sorbent: simple oxidation of styrene–divinylbenzene copolymer microparticles by Hummers method

Hummers method, a classical approach for preparation of graphitic oxide, was employed for the first time to prepare polymer-based uranium selective chelating sorbent by directly oxidizing styrene–divinylbenzene copolymer microparticles synthesized through the mix-solvothermal method in a mild binary solvent system. The resulting material was found rich in phenolic hydroxyl groups (17mmol/g) using techniques such as FT-IR and XPS. Batch adsorption experiments proved that the chelating sorbent exhibited excellent uranium selectivity from multi-ion solution containing 12 coexisting ions with 0.45mmol/g of uranium adsorption capacity accounting for up to 52% of the total adsorption capacity, while 373mg/g of the maximum adsorption capacity for the sorbent was obtained in the “pure” U(VI) ion solution. The proposed method has the advantages of simpleness, cheapness, and high yield of phenolic hydroxyl groups, which could provide a new and generally applicable approach for facile preparation of polyphenolic materials based on phenyl-rich polymer.

Biosorption of Copper, Zinc and Nickel From Multi-Ion Solutions

Abstract The biosorption of Cu(II), Zn(II) and Ni(II) by microscopic green algae Chlorella kessleri was investigated using batch experiments. Biosorption studies with single and multi ion solutions were carried out to study the effect of several ions on the biosorption of selected metal. The influence of zinc and nickel on copper biosorption, copper and nickel on zinc biosorption and zinc and copper on nickel biosorption were investigated. The Langmuir and Freundlich model were used to describe the adsorption equilibrium of studied metals on Chlorella kessleri biomass. Based on the experimental results it was found that the presence of copper increased the biosorption capacity of zinc from 48.6 mg/g to 96.8 mg/g and nickel from 29.3 mg/g to 62.7 mg/g, respectively. However, the presence of nickel decreased the biosorption capacity of zinc from 48.6 mg/g to 31.7 mg/g.

Sensors based on zirconia-modified perfluorinated sulfonic acid membranes sensitive to organic anions in multiionic aqueous solutions

The effect of modification of perfluorinated sulfonic acid membranes with zirconia on their conducting properties and electrode-active properties for potentiometric sensors whose analytical signal is the Donnan potential (DP) has been studied. It has been found that the incorporation of ZrO2 particles into the membrane matrix results in an increase in the ionic conductivity, as compared with unmodified membranes, and the proton diffusion coefficient changes nonmonotonically. Membranes with a gradient dopant distribution along the sample length provide for a partial decrease in the cation-exchange function of DP sensors because of a decrease in the concentration of fixed cation-exchange groups and due to the sorption of coions. This results in an increase in the sensor sensitivity to organic and sulfur-containing anions in multiionic aqueous solutions. Multivariate calibration methods with a nonorthogonal experimental design were used to evaluate the effects of the concentrations and nature of counterions and coions and pH in the test solutions on the characteristics of DP sensors.

Crossed mixture–process design approach to model nanofiltration rejection for non-dilute multi-ionic solutions in a given range of solution compositions

The goal of the present work is to illustrate the applicability of crossed mixture–process design to predict the rejection of the nanofiltration membranes when treating non-dilute solutions. The method used in this work is based on the use of mixture factors derived from the fractions of equivalents of the major ions present in solution combined with the total concentration as a process variable. In this way, polynomial models for permselectivity properties can be obtained. Model accuracy is improved by using pseudo-components to restrict the range of the composition variables to that expected for the feed water compositions. The experimental plan uses the D-optimal criterion. As an application example, the procedure was used to model the performance of the nanofiltration membrane NF270 (Dow-Filmtec) with ionic mixtures containing chloride, nitrate, sulfate, sodium and calcium. The experiments were carried out in a pilot plant with solutions of total concentration ranging from 2480 to 4050mg/L. The obtained polynomial models could satisfactorily describe individual ion rejection despite the solutions not being dilute. The polynomial models can be useful for design and operation purposes as an alternative to physical-based nanofiltration models.

A study of the capacitive deionisation performance under various operational conditions

Capacitive deionisation (CDI) has many advantages over other desalination technologies due to its low energy consumption, less environmental pollution and low fouling potential. The objectives of this study are to investigate the effect of operational conditions on the CDI electrosorption efficiency and energy consumption, to identify ion selectivity in multi-ionic solutions and to probe the effect of dissolved reactive silica on the treatment efficiency. A series of laboratory scale experiments were conducted using a CDI unit with activated carbon electrodes. The electrosorption removal efficiency was inversely related to solution temperature, initial total dissolved salts (TDS) concentration and the applied flow rate. CDI energy consumption (kWh/m3) is directly related to the TDS concentration and inversely related to the flow rate. The kinetics analysis indicated that the electrosorption followed pseudo-first-order kinetics model. Ion selectivity on activated carbon electrodes followed the order of Fe3+>Ca2+>Mg2+>Na+ for cations and SO42−>Br−>Cl−>F−>NO3− for anions. It was found that the dissolved silica was not removed by CDI; no silica fouling was found. The deterioration of activated carbon electrodes was not observed at any time during experiment.

Multi-ionic nanofiltration of highly concentrated salt mixtures in the seawater range

This work presents experimental observations on the permeation of multi-ionic solutions through a commercial DESAL-HL nanofiltration membrane. Two types of mixed-salt solutions have been analysed with a common co-ion (NaCl + Na 2SO 4) and with a common counter-ion ((NaCl + MgCl 2)). The NaCl concentrations have been similar to those of seawater with divalent ions with lower concentrations up to a tenth of that of the monovalent salt. In this study, SEDE-VCh model that includes the variation of the charge inside the membrane pores has been used to model the system and structural, electrical and dielectrical membrane parameters for such systems have been obtained. We show that accurate enough predictions can be achieved for the retention of monovalent ions in the presence of counter or co-ion divalent ions from the single NaCl salt results. While correct predictions for the retention of the divalent ions require membrane charges and dielectric constants dependent of the ionic composition of the solutions filtered.

Limiting current density in the electrodialysis of multi-ionic solutions

The aim of this work was the development of an explicit model to estimate the limiting current density in the electrodialysis of dilute multi-ionic solutions. The model assumes that the ionic transport occurs in a film layer adjacent to an ion exchange membrane and it is quantified by a linearized form of the Nernst–Planck (NP) equations together with the electroneutrality requirement at the solution/ion exchange membrane interface. An explicit expression for the limiting current density of a dilute multi-ionic solution was derived, involving a mass-transfer coefficient based on an effective diffusivity of the multi-ionic solution. The model further assumes that the steric exclusion of the ions by the membrane is negligible, and thereby the limiting current density is attained when the concentration of each and every ion is null at the solution/membrane interface. The model predictions for the limiting current density were compared with experimental data of single salt solutions (MgCl 2) and multi-ionic solutions (MgSO 4 + MgCl 2) in a bench-scale electrodialysis unit (EUR2C-7P18, Eurodia, France) for various Reynolds numbers and salts concentrations. The average relative deviations between the model predictions and the experimental data were lower than 13% for MgCl 2 solutions (10, 20 equiv./m 3) and solutions of MgSO 4 + MgCl 2 (5 + 5, 10 + 10 equiv./m 3). The dimensionless limiting current density and the counterions transport numbers predicted by the linearized and non-linear Nernst–Planck equations were also compared for a broad range of dimensionless operating parameters and a fair to good agreement was observed between the two approaches.

Nanofiltration of multi-ionic solutions: prediction of ions transport using the SEDE model

This work focuses on the application of nanofiltration (NF) to the concentration of a pharmaceutical product, Clavulanate (), from clarified fermentation broths, which show a complex composition with six main identified ions (, , , , and ), glucose and glycerol. The solutes transport through the NF membrane pores was investigated using the SEDE (Steric, Electric and Dielectric Exclusion) model. This model was applied to predict the rejection rates of the initial feed solution and the final concentrated solution (10-fold concentrated solution). The best results were achieved with a single fitted parameter, (the dielectric constant of the solution inside pores) and considering that the membrane selectivity is governed by steric, electric (Donnan) and Born dielectric exclusion mechanisms. While the predicted intrinsic rejections of solutions comprising up to six ions and uncharged solutes were in good agreement with the experimental values, the deviations were much larger for the 10-fold concentrated solution.

Influence of coion and counterion size on multi-ionic solution nanofiltration

Nanofiltration of a solution containing four monovalent ions has been carried out to assess the Donnan steric and dielectrical exclusion pore model (DSDE-PM). The sequences of the ions rejections were Li + > Cl − > IO 3 − > K + and IO 3 − > K + > Li + > Cl − when membrane was positive or negative charged, respectively. Several types of ionic radii were implemented either in the interfaces equilibrium or in transport equations and the Stokes radius gave the best fitting, followed by a model that takes cavity radius for DE and crystal radius for the rest of hindrance factors. Analysis of the model equations showed that for high charge membrane, counterion with the highest mobility inside the pores is more rejected than the slowest one. The sequence of coions rejections is more difficult to predict as it depends on the relative contribution of mobility and several hindrance factors as well.

Investigating nanofiltration of multi-ionic solutions using the steric, electric and dielectric exclusion model

The aim of this work was to test the ability of the steric, electric and dielectric exclusion (SEDE) model to describe the separation of multi-ionic solutions (3 and 4 ions) by nanofiltration. To this end, mixed solutions of Pb ( NO 3 ) 2 and Co ( NO 3 ) 2 · 6 H 2 O at various pH were filtered through a nanofiltration polyamide membrane. The structural features of the membrane active layer were inferred from glucose rejection rates and water permeability. The charge state of the membrane active layer was evaluated for the various solutions from coupled tangential streaming potential (TSP) and electric conductance measurements. Calculations were carried out using different approaches. Modelling results show that the experimental rejection rates are not well described incorporating the two types of dielectric exclusion mechanisms, i.e. Born dielectric effect and image forces contribution, in the steric/electric model. However, the description is found to be satisfactory considering (i) steric, electric and Born dielectric exclusion mechanisms, with two fitted parameters: the effective volume charge density, X, and the dielectric constant of the solution inside the pores, ε p , or (ii) steric, electric exclusion mechanisms and image forces, with two fitted parameters, X and the dielectric constant of the active layer material, ε m . ε p and ε m were assessed in the range of 56.3–74.6 and 7–10, respectively. The values of 7–10 for ε m are different from the commonly used value for dry polyamide (i.e. ε m = 3 ). It might be due to the wetting of the polymer. In both approaches, the fitted values of X were found to be smaller than X values inferred from TSP measurements, which is in agreement with the charge regulation phenomenon.

Xylem embolism alleviated by ion-mediated increase in hydraulic conductivity of functional xylem: insights from field measurements

Recent studies have shown that, in some species, xylem hydraulic conductivity (K(h)) increases with increasing cation concentration of xylem sap. Evidence indicates that K(h) increases as a result of the de-swelling of pit membrane pectins caused by cation neutralization of polygalacturonanes. We tested whether this ionic effect partly compensates for the embolism-induced loss of stem hydraulic conductivity (PLC) by increasing K(h) of functioning conduits. We report changes in PLC, leaf water status and potassium concentration ([K(+)]) of xylem sap measured in April and July in two evergreens (Ceratonia siliqua L. and Phytolacca dioica L.) and one deciduous tree (Platanus orientalis L.) growing in the field in Sicily. In summer, Ceratonia siliqua and Phytolacca dioica showed similar native embolism (PLC = 30-40%) and [K(+)] of xylem sap (14 to 17 mM), and K(h) of stems perfused with 10 to 25 mM KCl increased by 15 to 18% compared with K(h) of stems perfused with a low concentration of a multi-ionic solution. In contrast, native [K(+)] of sap of Platanus orientalis was 50% of that in the two evergreens in summer, with a parallel lack of detectable changes in PLC that was below 10% in both spring and summer. The ionic effect was PLC-dependent: the enhancement of K(h) induced by 10 to 25 mM KCl changed from 15% for fully hydrated stems to 50-75% for stems with PLC = 50%. In Ceratonia siliqua, PLC was less than 10% in spring and about 40% in summer; concurrently, xylem sap [K(+)] increased from 3 to about 15 mM. This [K(+)] at the recorded PLC would cause an increase in residual K(h) of about 30%. Hence, the actual reduction in water transport capacity of Ceratonia siliqua stems in summer is about 20%. Similar calculations for Phytolacca dioica suggest that the actual loss of hydraulic conductivity in stems of this species in summer would be only about 10%, and not 30% as suggested by hydraulic measurements performed in the laboratory. We conclude that an increase in [K(+)] of xylem sap might be involved in the up-regulation of residual K(h), thus substantially alleviating the embolism-induced reduction in leaf water supply.

Modelling the separation by nanofiltration of a multi-ionic solution relevant to an industrial process

The current work focuses on the application of nanofiltration (NF) to the isolation of a pharmaceutical product, clavulanate (CA −), from clarified fermentation broths, which show a complex composition with five main identified ions (K +, Cl −, NH 4 +, SO 4 2− and CA −). Our aim is to predict the rejection rates of these five ions, with the NF membrane Desal-DK, which may influence the separation of CA − and play a role in the whole downstream process. Concentration polarization of this multi-ionic solution was addressed both through the application of the extended Nernst–Planck equations in the film layer, assuming limiting values for the boundary layer thickness, and by applying a new methodology which dispenses this arbitrary assumption. The latter approach was chosen to calculate the intrinsic rejection rates. The transport through the membrane pores was modelled using the Steric, Electric, Dielectric and Exclusion (SEDE) model in order to predict the intrinsic rejections of the five ions in solution. The membrane volume charge density was assessed from tangential streaming potential measurements for the system membrane/five ions solution. With a single fitted parameter, ɛ p (the dielectric constant of the solution inside pores) and considering that the ion selectivity is governed by steric, Donnan and Born dielectric exclusion mechanisms, the predicted intrinsic rejections rates of the five ions are in good agreement with the experimental values.