ELECTRO-DEIONIZATION OF Cr (VI)-CONTAINING SOLUTION. PART II: CHROMIUM TRANSPORT THROUGH INORGANIC ION-EXCHANGER AND COMPOSITE CERAMIC MEMBRANE

Cr (VI) transport through a composite ceramic membrane containing an ion-exchange component, namely xerogel of hydrated zirconium dioxide, was investigated. The diffusion coefficient of Cr (VI) species through the membrane, which has been determined under open circuit conditions, is 1.80 × 10^?10 m² s^?1. The transport number of Cr (VI) species through the ceramic membrane was found to rise with increasing voltage and reached 0.17 under “over-limiting current” conditions. On the other hand, the transport of chromate ions through hydrogel of hydrated zirconium dioxide becomes more intensive with a decrease in potential drop through the system involving ion-exchanger bed and ceramic membrane due to decrease in the membrane resistance. The diffusion coefficient of Cr (VI) ions in hydrogel of the inorganic ion exchanger was estimated as 4.36 × 10^?12 m² s^?1. A possibility of Cr (VI) removal from a weakly acidic diluted solution using an electro-deionization method was shown: the degree of solution purification was found to reach 50%. The transport of species is realized through both the solution and the ion exchanger.     

Application of Cr(VI) transport across the polymer inclusion membrane with calixresorcin[4]arene derivative as ion carrier

ABSTRACT

In this study, the experiments were performed to evaluate the Cr(VI) removal efficiency by transport across the polymer inclusion membrane with calixresorcin[4]arene derivative as ion carrier. The several influence factors such as carrier concentration, the amount of plasticizer in the membrane as well the effect of acid type and its concentration in source phase and the membrane stability were investigated. It was found that the immobilized calixresorcin[4]arene derivative in membranes effectively extracted chromium from acidic media. Under optimized conditions, the Cr(VI) removal efficiency was 98.4%.     

The comprehensive investigation of the room temperature ionic liquid additives in PVC based polymer inclusion membrane for Cr(VI) transport

This study is to perform the comprehensive investigation of PVC based ionic plasticized membrane (IPM) production by using room temperature ionic liquid (RTIL)‐based additives and the membrane application of selective Cr(VI) removal. Some significant parameters related to membrane structures that are membrane thickness, plasticizer rate, and type, RTILs rate, and type, the average molecular weight of PVC were studied to define the excellent polymeric membrane film composition. After that, the PVC based polymeric film used in the Cr(VI) transport and initial mass transfer coefficient (J_o) were about 3.57 × 10^?7 mol s^?1 m^?2 by decyl substituted RTIL as an additive. Also, optimized membrane transport process has been considered as selective enough for Cr(VI) in the presence of the other heavy metal ions. Surface characterizations of the membranes have been performed to clarify the structural and the morphological assessment of IPMs at initial and end of Cr(VI) transport by SEM‐EDX, AFM, contact angle measurement and found a good relationship between the molecular structure of RTIL additive and membrane morphology. As we know that lots of researchers are still trying to find environmentally friendly, inexpensive and straightforward processes to remove toxic substances from industrial effluents or natural sources. At that point, our results can open a gate for cheap, novel and environmentally friendly Cr(VI) removal by PVC based membrane. J. VINYL ADDIT. TECHNOL., 25:E107–E119, 2019. © 2018 Society of Plastics Engineers     

Ageing of ion-exchange membranes in oxidant solutions

In electrodialysis processes, membranes tend to loose some transport properties after a certain period of utilization. Two ion-exchange membranes, namely a homogeneous anion-exchange membrane (MX) and a heterogeneous cation-exchange membrane (MK-40), were used to investigate the ageing phenomenon and to highlight the characteristic parameters of these membranes which evolve most quickly with ageing. An artificial ageing was carried out under oxidizing conditions (i.e. peracetic acid, and P3 Active Oxonia^® solutions) on both membranes. It was found that an increase in conductivity and swelling rate, implying a modification of the polymer chain structure with time, but without a significant deterioration of the functional groups since the exchange capacity remained almost constant.     

Transport of Chromium(VI) through a Supported Liquid Membrane Containing Tri-n-octylphosphine Oxide

ABSTRACT

In this study the transport of chromium(VI) from aqueous solutions of pH 2–4 through a supported liquid membrane (SLM) with tri-n-octylphosphine oxide (TOPO) dissolved in kerosene as a mobile carrier was investigated. The transport flux of Cr(VI) increased with an increase in the concentrations of Cr(VI) in the feed phase and of TOPO in the membrane phase, but with a decrease in pH of the feed phase. Considering the equilibria of various Cr(VI) species in the aqueous phase and of the Cr(VI)—TOPO complexes formed in the membrane phase, a permeation model including the aqueous film diffusion of HCrO₄ ^? and Cr₂O₇ ^2? toward the membrane, the interfacial chemical reaction between them and TOPO, and the membrane diffusion of the Cr(VI)—TOPO complexes (H₂CrO₄(TOPO) and H₂Cr₂O₇(TOPO)₃) was proposed to describe the transport of Cr(VI) through the SLM. By best fitting the transport flux equations of Cr(VI) with the experimental data using the Rosenbrock method, the apparent mass-transfer coefficients of HCrO₄ ^? and Cr₂O_7^. across the aqueous film, and those of H₂CrO₄(TOPO) and H₂Cr₂O₇(TOPO)₃ across the membrane phase, were obtained. This work helps to clarify the transport mechanism of Cr(VI) through an SLM.     

Ion and water transport properties of cation exchange membranes prepared by heavy-ion-track grafting technique

ABSTRACT

For high-performance electrodialysis of saline water, cation exchange membranes (CEMs) that actively transport Na⁺ and restrict water permeation are required. In this study, we prepared novel CEMs by a heavy-ion-track grafting technique and measured their membrane resistance and water permeation flux as transport properties. The prepared nanostructured CEMs exhibited lower resistance and lower water flux than the commercial CEM. Na⁺ ions were efficiently transported through their unique one-dimensional ion channels (low resistance), while water transport was suppressed due to the very low water uptake of the CEMs. These results demonstrated the high potential of these nanostructured CEMs for use in practical saline water electrodialysis.     

Transport of Cr(VI) from HCl Media Using (PJMTH+Cl−) Ionic Liquid as Carrier by Advanced Membrane Extraction Processing

The transport of Cr(VI) from acidic media through pseudo-emulsion based membrane strip dispersion (PEMSD) containing the ionic liquid (PJMTH⁺Cl^?) as carrier in the form of a pseudo-emulsion with sodium hydroxide has been investigated. The ionic liquid was generated in situ by reaction of the primary amine Primene JMT and HCl. The transport of Cr(VI) is evaluated as a function of various experimental variables: stirring speed in the feed phase, concentration of Cr(VI) and HCl in the feed phase, carrier concentration, and organic diluents in pseudo-emulsion, and NaOH concentration in pseudo-emulsion as strippant. In PEMSD, pseudo-emulsion is an emulsion that is formed temporarily between the organic and the stripping solutions. Both solutions are separated when the stirring device is stopped. The value of the overall permeation coefficient obtained under standard experimental conditions was 3.1 × 10^?3 cm s^?1, whereas the transport process is controlled by diffusion of chromium species in the stagnant film of the feed phase. The performance of the system against other carriers (amines, quaternary phosphonium salt and quaternary ammonium salt) was also evaluated.     

Nitric acid and sodium hydroxide generation by electrodialysis using bipolar membranes

An electrodialysis process with bipolar membranes was used to generate HNO3 and NaOH from NaNO3 which can be found in industrial waste waters. The current efficiency of this process is limited by proton leakage through the anion exchange membrane (AEM), co-ion leakage through bipolar membranes (BPM) and water transport through the ion exchange membranes. Three cell configurations using three or two compartment cells with different anion or cation exchange membranes (CEM) in stack series were used and compared. Electrodialysis with three compartments gives the best current efficiencies for nitric acid and sodium hydroxide production from sodium nitrate.     

Structural effects of ion‐exchange membrane on the separation of L‐phenylalanine (L‐Phe) from fermentation broth using electrodialysis

The effects of membrane structure on the separation of L ‐phenylalanine (L ‐Phe) by electrodialysis from a fermentation broth and on the fouling tendency were investigated in this study. Two anion‐exchange membranes (Neosepta AFX and AM‐1, Tokuyama, Japan) were selected and characterized using the chronopotentiometry method. For a fresh membrane, AFX showed a lower electrical resistance and a lower permselectivity than AM‐1. After being fouled with humic acid, however, the electrical resistance of AFX was higher than that of AM‐1. The L ‐Phe selectivities for both membranes were lower than those of the fresh membranes. The result may be attributed to the structural difference between AFX and AM‐1 membranes. AFX has a lower repulsion force against the co‐ion and could be more strongly affected by the foulants than AM‐1 because AFX has a more porous structure than AM‐1. Experiments on the separation of L ‐Phe from the fermentation broth were carried out using two different stack configurations, ie desalting electrodialysis and water‐splitting electrodialysis. It was observed that the recovery efficiency of L ‐Phe through electrodialysis for 100 min reached 95% for AFX and 85% for AM‐1. In the desalting configuration of electrodialysis, the solution pH must be adjusted to alkaline conditions to recover the L ‐Phe through the anion‐exchange membrane. On the contrary, it was possible to recover the L ‐Phe without adjustment of the solution pH in the water‐splitting electrodialysis because OH^? generated from the bipolar membrane converted neutral L ‐Phe into an anion. © 2002 Society of Chemical Industry     

Electrodialytic properties of aromatic and aliphatic type hydrocarbon-based anion-exchange membranes with various anion-exchange groups

Anion-exchange membranes (AEMs) with various membrane structures were prepared by introducing various amines: trimethylamine (TMA), triethylamine (TEA), tri-n-propylamine (TPA) and tri-n-butylamine (TBA) into precursor membranes prepared from chloromethylstyrene (CMS)–divinylbenzene (DVB) and glycidyl methacrylate (GMA) – DVB. Their properties for ionic transport and anti-organic fouling were examined. Almost all of the prepared AEMs have excellent ionic transport properties: transport number of anions >0.94 and membrane resistance <4 Ωcm². The voltage change through the AEMs during electrodialysis operation using solutions containing sodium dodecylbenzene-sulfonate as a foulant indicated that there are three cases of fouling mechanism being related to membrane structure: (a) aliphatic AEMs show lower fouling than aromatic ones; (b) the lower the water content of an AEM, the more remarkable the fouling; (c) the longer the chain length of the alkyl groups of the anion-exchange groups of an AEM, the more remarkable the fouling.     

LONG-TERM PERFORMANCE OF HOLLOW FIBRE MEMBRANE SOLVENT EXTRACTION MODULES USED FOR Cr(VI) RECOVERY FROM ELECTROPLATING RINSE WATER

ABSTRACT

The long-term performance of a hollow fibre membrane solvent extraction unit has been investigated for the recovery of Cr(VI) from plating rinse water. A pilot scale experiment was performed in a local electro-plating plant using-membrane modules with an area of 0·17 m². The separation of Cr(VI) from the rinse liquor was carried out in two hollow fibre membrane modules, and is compared with a single module supported liquid membrane (SLM) which was also used in the same service. The Cr(VI) flux declined gradually to half the initial value after 25 days. This was found to be due to the membrane fouling combined with the degradation of organic solvent. The loss of organic solution was initially severe but stabilized after a few days and became negligible. The flux in the SLM mode appeared similar but the life time was very short, less than a day, however continuous operation was attainable by periodic replenishment of the membrane. Using both designs, it has been shown that Cr(VI) could be extracted from dilute feed into the stripping solution with an enrichment factor of 10 – 20 times using this technique.     

Carrier-Mediated Transport of Molybdenum(VI) through Supported Liquid Membranes

Abstract

The liquid membrane transport of Mo(VI) from an acidic solution into an alkaline stripping solution was carried out by using a mobile carrier, 5,8-diethyl-7-hydroxy-dodecan-6-one oxime (LIX 63). Further transport of MoO₄ ^2? from the alkaline solution was performed by using another carrier, trioctylmethylammonium chloride (TOMAC). Molybdenum(VI) was effectively transported through double membranes composed of LIX 63/dilute NaOH solution/TOMAC from a feed solution (10^?3 M HNO₃) into a product solution (1 M NaOH). Molybdenum(VI) was concentrated with high recovery into a small volume of product solution. The separation of Mo(VI) from several ions was performed by means of the double membranes.     

Permeation of Chromium(VI) and Rhenium(VII) Oxyanions through Liquid Organic Membranes Facilitated by Quaternary Ammonium Chlorides

Abstract

An experimental investigation is presented on the facilitated transport of Cr(VI) and Re(VII) oxyanions from aqueous solution into and through organic solutions of quaternary ammonium chlorides as mobile carriers of anions. Trimethyl tallow ammonium chloride (Aliquat 26), dimethyl dicoco ammonium chloride (Aliquat 221), and methyl tricapryl ammonium chloride (Aliquat 336) from General Mills Chemicals have been investigated. Effects of both anions and mobile carriers as well as the pH of feed aqueous solution and mixing rate on the course of metal permeation have been established. The hydrophobicity and nucleophilicity of a quaternary ammonium chloride were found to be the key factors influencing the transport of Cr(VI) and Re(VII) anions through bulk and emulsified liquid organic membranes. The permeation of perrhenates was much faster than that of chromates. Fast and effective separation was determined to be possible for rhenium from chromium in aqueous solution by means of facilitated transport of their oxyanions across liquid surfactant membranes.     

Separation of Palladium(II) and Platinum(IV) by Bulk Liquid Membranes during Electrodialysis

Abstract

The process of PdCl₄ ^2? and PtCl₆ ^2? separation extracting from binary hydrochloric mixtures as well as palladium(II) extraction from individual solutions by bulk liquid membranes containing diphenylthiourea and di‐o‐tolylthiourea in 1,2‐dichloroethane is studied at galvanostatic electrodialysis. The effects of the current density, the composition of the liquid membrane and of aqueous solutions on the rate of the metal transport are determined. It is shown that an effective separation of Pt(IV) from Pd(II) is achieved in the presence of an excess of the carrier. Maximum separation factor β_Pt/Pd of 380 is obtained in 1 hour of electrodialysis under optimal conditions. The transport of platinum(IV) is supposed to occur in the form of ionic associates (PdL₄Cl)₂PtCl₆. Platinum(IV) concentration and composition of the strip solution do not exert a considerable influence on the separation factor.     

Comparative performance of ion exchange membranes for electrodialysis of nickel and cobalt

The extraction of nickel and cobalt from their sulfate solutions by electrodialysis in a modified three compartment cell is described. Two cation exchange membranes, the perfluorosulfonic Nafion® 117 and a new sulfonated PVDF membrane, are compared under similar operating conditions. The membranes are used as either flat structures or as corrugated structures. The effect of flow rate, current density, salt concentration and temperature on the performance of each membrane is described. The performance is characterised in terms of transport properties, current efficiencies and concentrations of metal ions transported through each membrane. The performance of the PVDF membrane was as good as; if not slightly better, than that of the commercial Nafion 117. A significant improvement with the use of corrugated membranes on the amounts of metal extracted is observed. The corrugated Nafion 117 membrane gave superior current efficiencies compared to the flat one with the same amount of charged passed. Separation of cobalt from nickel by electrodialysis in mixed solution has also been investigated.     

Use of bulk liquid membrane for the removal of chromium (VI) from aqueous acidic solution with tri-n-butyl phosphate as a carrier

Tri-n-butyl phosphate (TBP) was used as carrier for the transport of chromium (VI) through a hexane bulk liquid membrane. The transport efficiency of chromium (VI) by TBP was investigated under various experimental conditions such as pH of the feed phase (Cr (VI) solution), concentration of the receiving phase (NaOH solution), concentration of TBP in membrane, rate of stirring, effect of transport time, type of solvent, Cr (VI) concentration in feed phase, and effect of temperature. The transport efficiency increased with increasing carrier concentration from 7.5 × 10^− 2 to 2.25 × 10^− 1 mol/L. At high pH (donor phase) the transport rate of chromate ions decreased. At high stirring speed (300 rpm) the Cr (VI) transport from the feed phase to the strip phase was completed within 5 h at 27 °C. Under optimum conditions: donor phase 4.8 × 10^− 4 mol/L K₂Cr₂O₇ solution at pH 1.0 ± 0.1, acceptor phase 1.0 mol/L NaOH solution, membrane phase 2.25 × 10^− 1 mol/L, stirring speed 300 rpm, and temperature 27 °C, the flux rate was found to be 2.90 × 10^− 7 mol/m² s.     

Modelling the transport of carbonic acid anions through anion-exchange membranes

Electrodiffusion of carbonate and bicarbonate anions through anion-exchange membranes (AEM) is described on the basis of the Nernst-Planck equations taking into account coupled hydrolysis reactions in the external diffusion boundary layers (DBLs) and internal pore solution. The model supposes local electroneutrality as well as chemical and thermodynamic equilibrium. The transport is considered in three layers being an anion exchange membrane and two adjoining diffusion layers. A mechanism of competitive transport of HCO₃⁻ and CO₃²⁻ anions through the membrane which takes into account Donnan exclusion of H⁺ ions is proposed. It is predicted that the pH of the depleting solution decreases and that of the concentrating solution increases during electrodialysis (ED). Eventual deviations from local electroneutrality and local chemical equilibrium are discussed.     

Study on Competitive Transport of Heavy Metal Ions Through Liquid Surfactant Membrane

Abstract

In the present work an attempt has been made to develop a mathematical model for competitive transport of Cr(VI) and Mo(VI) through liquid surfactant membrane from acidic solution using Alamine‐336 and Caustic Soda as extractant and stripping reagent respectively. A reaction front has been assumed to exist within the emulsion globule in the proposed model. It has been assumed that, an instantaneous and irreversible reaction takes place at the membrane‐internal stripping phase interface between the solute and internal stripping reagent. Experiments on simultaneous extraction of Cr(VI) and Mo(VI), in batch mode, from aqueous solutions of Potassium Dichromate and Ammonium Molybdate have been carried out with the initial concentration of the solutes between 50–100 mg/l. Experiment on emulsion stability has also been performed to arrive at a reasonably stable emulsion composition. Effect of initial solute concentration on distribution coefficient has also been found experimentally and fitted by a semiemperical model that has been used in the computer simulation of the simultaneous extraction process. It has been found that the experimental results are within reasonably close proximity with the simulated curves.     

ELECTRO-DEIONIZATION OF Cr (VI)-CONTAINING SOLUTION. PART I: CHROMIUM TRANSPORT THROUGH GRANULATED INORGANIC ION-EXCHANGER

Kinetics of Cr (VI) → OH^? exchange on both hydrogel and xerogel of hydrated zirconium dioxide was investigated. Self-diffusion coefficient of Cr (VI) species has been determined by analysis of kinetic curves. Transport of Cr (VI) anions through the inorganic ion exchangers under the influence of applied voltage was also researched. In the case of hydrogel, the ions are transported mainly through the solid phase. Diffusion coefficient of chromate anions through this material was estimated as 9.00 × 10^?12 m² s^?1. This is in agreement with self-diffusion coefficient of Cr (VI) obtained from kinetic measurements (1.60 × 10^?12–9.92 × 10^?12 m² s^?1). Owing to the rather high mobility of Cr (VI) through hydrogel of hydrated zirconium dioxide, this material was recommended for electro-deionization processes. On the other hand, the use of polymer anion-exchange membrane must be excluded to prevent poisoning of the inorganic ion exchanger with Cr (III) cations to be formed during chemical interaction of Cr (VI) with organic materials.     

Application of polypyrrole coated on wood sawdust for removal of Cr(VI) ion from aqueous solutions

In this study polypyrrole (PPy) was synthesised chemically on the surface of sawdust that has already been soaked with monomer solution (pyrrole). FeCl₃ were used as chemical oxidants for oxidation of pyrrole into polymer (PPy/Cl). The sawdust coated by PPy (PPy/SD) was used as an efficient sorbent for removal of Cr(VI) ion from aqueous solutions. It was found that PPy/SD is very easy and simple to prepare and can be used as an effective sorbent for removal of Cr(VI) from water and wastewater solutions. The Cr(VI) removal is assumed to be mainly due to the anion exchange properties of the polymer which is formed as PPy⁺/Cl⁻. The introduced sorbent in this paper shows that PPy/SD can be used to eliminate or separate anionic contaminations from aqueous solutions under open circuit conditions.