Waste acid recovery utilizing monovalent cation permselective membranes through selective electrodialysis

Selective electrodialysis(SED)has surfaced as a highly promising membrane separation technique in the realm of acid recovery owing to its ability to effectively separate monovalent ions through the utilization of a potential difference.However,the current SED process is limited by conventional commercial monovalent cation permselective membranes(MCPMs).This study systematically investigates the use of an independently developed MCPM in the SED process for acid recovery.Various factors such as current density,volume ratio,initial ion concentration,and waste acid systems are considered.The independently developed MCPM offers several advantages over the commercial monovalent selective cation-exchange membrane(CIMS),including higher recovered acid concentration,better ion flux ratio,improved acid recovery efficiency,increased recovered acid purity,and higher current efficiency.The SED process with the MCPM achieves a recovered acid of 95.9%and a concentration of 2.3 mol·L^(–1) in the HCl/FeCl_(2) system,when a current density of 20 mA·cm^(-2) and a volume ratio of 1:2 are applied.Similarly,in the H_(2)SO_(4)/FeSO_(4) system,a purity of over 99%and a concentration of 2.1 mol·L^(–1) can be achieved in the recovered acid.This study thoroughly examines the impact of operation conditions on acid recovery performance in the SED process.The independently developed MCPM demonstrates outstanding acid recovery performance,highlighting its potential for future commercial utilization.

Performance comparison of lithium fractionation from magnesium via continuous selective nanofiltration/electrodialysis

Although selective nanofiltration(SNF)and selective electrodialysis(SED)have been widely adopted in the field of Mg^(2+)/Li^(+)separation,their differences have not been illustrated systematically.In this study,for the first time,SNF and SED processes in continuous mode were studied for Li+fractionation from the same brine with high Mg/Li ratios and their differences were discussed in detail.For a fair analysis of the two processes,typical factors were optimized.Specifically,the optimal operating pressure and feed flow rate for SNF were 2.4 MPa and 140 L·h^(-1),respectively,while the optimal cell-pair voltage and replenishment flow rate for SED were 1.0 V and 14 L·h^(-1),respectively.Although the Li^(+)fractionation capacity of the two processes were similar,the selectivity coefficient of SNF was 24.7% higher than that of SED and,thus,the Mg/Li ratio in purified stream of the former was 19.0% lower than that of the latter.Due to higher ion driving force,SED had clear advantages in recovery ratio and concentration effects.Meanwhile,the specific energy consumption of SED was 20.1% lower than that of SNF.This study provided a better understanding and guidance for the application and improvement of the two technologies.

Studies of Adsorption of Cadmium Ions by Biowaste Adsorbent from Aqueous Solutions with Ion-Selective Electrodes and ICP-OES

Using environment-friendly and low-cost biowaste adsorbents as toxic metal ion removal substrates from aqueous solutions has a great economic advantage. This work evaluated pumpkin and potato peel biowastes for the adsorption of cadmium ions. The biowastes were treated with acid or base. Batch experiments were carried out by introducing a known concentration of metal ion solution into the biowaste sorbent at various pH levels. The pH and metal ion concentration was monitored with pH and cadmium ion-selective electrode continuously for two hours, and the final concentration for the metal ion after 24 hours was measured with the cadmium electrode and then confirmed with ICP-OES. L-type isotherms were obtained that fit to Freundlich model. Adsorption isotherms showed chemical adsorption and the kinetics following the second order model. Equilibrium adsorption capacity is higher than 29 mg/g at pH 5.6 when the initial concentration is 220 ppm. Dynamic cadmium adsorption capacity is 17 mg/g from aqueous solution when the feed solution is 220 ppm with pumpkin peel biowaste sorbent. The biowaste materials can be regenerated with acid washing.

Acid precipitation coupled electrodialysis to improve separation of chloride and organics in pulping crystallization mother liquor

Inefficient separation of inorganic salts and organic matters in crystallization mother liquor is still a problem to industrial wa stewater treatment since the high salinity significantly impedes organic pollutant degradation by oxidation or incineration.In the study,acidification combined electrodialysis(ED)was attempted to effectively separate Cl-ions from organics in concentrate pulping wastewater.Membrane’s rejection rate to total organic carbon(TOC)was 85%at wastewater intrinsic pH=9.8 and enhanced to 93%by acidifying it to pH=2 in ED process.Negative-charged alkaline organic compounds(mainly lignin)could be liberated from their sodium salt forms and coagulated in acidification pretreatment.Neutralization of the organic substances also made their electro-migration less effective under electric driving force and in particular improved separation efficiency of chloride and organics.After acid-ED coupled treatment(pH=2 and J=40 mA·cm-2)[TOC]remarkably reduced from 1.315 g·L-1 to 0.048 g·L-1 and[Cl-]accumulated to 130 g·L-1 in concentrate solution.Recovery rate of NaCl was 89%and the power consumption was 0.38 kW·h·kg-1 NaCl.Irreversible fouling was not caused as electric resistance of membrane pile maintained stably.In conclusion,acidic-ED is a practical option to treat salinity organic wastewater when current techniques including thermal evaporation and pressure-driven membrane se paration present limitations.

Using bipolar membrane electrodialysis to synthesize di-quaternary ammonium hydroxide and optimization design by response surface methodology

Bipolar membrane electrodialysis(BMED) has already been described for the preparation of quaternary ammonium hydroxide. However, compared to quaternary ammonium hydroxide, di-quaternary ammonium hydroxide has raised great interest due to its high thermal stability and good oriented performance.In order to synthesize N,N-hexamethylenebis(trimethyl ammonium hydroxide)(HM(OH)_2) by EDBM,experiments designed by response surface methodology were carried out on the basis of single-factor experiments. The factors include current density, feed concentration and flow ratio of each compartment(feed compartment: base compartment: acid compartment: buffer compartment). The relationship between current efficiency and the above-mentioned three factors was quantitatively described by a multivariate regression model. According to the results, the feed concentration was the most significant factor and the optimum conditions were as follows: the current efficiency was up to 76.2%(the hydroxide conversion was over 98.6%), with a current density of 13.15 m A·cm^(-2), a feed concentration of 0.27 mol·L^(-1) and a flow ratio of 20 L·h^(-1):26 L·h^(-1):20 L·h^(-1):20 L·h^(-1) for feed compartment, base compartment, acid compartment, and intermediate compartment, respectively. This study demonstrates the optimized parameters of manufacturing HM(OH)_2 by direct splitting its halide for industrial application.

The Measurement of Membrane Potential and NO3 Activity in Root Cells Using Ion-Selective Microelectrodes

Remobilisation of nitrate in plants, especially in vacuole of plant, is mostly related to the qua- lity of agricultural products and the high nitrogen use efficiency in plants. Ion-selective microelectrodes offer a non-destructive and non-interruptive method to measure NO 3 gradients and electric potential differences across both the plasma membrane and tonoplast. Thus, a double-barrelled microelectrode backfilled with a membrane sensor for NO 3 embedded in poly vinyl chloride (PVC) can record the NO 3 activity in cytoplasm and vacuole of a cell. This paper presented how to make this kind of microelectrode and how to do the intracellular measurements on intact plants. Our result showed that nitrate activity was about 2.7 mmol L 1 in cytoplasm while 70 mmol L 1 in vacuole, which implicated that vacuole was a pool of nitrate in plants.

Production of antihypertensive and antidiabetic peptide fractions from quinoa(Chenopodium quinoa Willd.)by electrodialysis with ultrafi ltration membranes

Processing bioactive peptides from natural sources using electrodialysis with ultrafiltration membranes(EDUF)have gained attention since it can fractionate in terms of their charge and molecular weight.Quinoa is a pseudo-cereal highlighted by its high protein content,amino acid profile and adapting growing conditions.The present work aimed at the production of quinoa peptides through fractionation using EDUF and to test the fractions according to antihypertensive and antidiabetic activity.Experimental data showed the production of peptides ranging between 0.4 and 1.5 k Da.Cationic(CQPF)(3.01%),anionic(AQPF)(1.18%)and the electrically neutral fraction quinoa protein hydrolysate(QPH)-EDUF(~95%)were obtained.In-vitro studies showed the highest glucose uptake modulation in L6 cell skeletal myoblasts in presence of QPH-EDUF and AQPF(17%and 11%)indicating potential antidiabetic activity.The antihypertensive effect studied in-vivo in spontaneously hypertensive rats(SHR),showed a decrease in systolic blood pressure in presence of the fractionated peptides,being 100 mg/kg a dose comparable to Captopril(positive control).These results contribute to the current knowledge of bioactive peptides from quinoa by reporting the relevance of EDUF as tool to produce selected peptide fractions.Nevertheless,further characterization is needed towards peptide sequencing,their respective role in the metabolism and scaling-up production using EDUF.

Direct Determination of Potassium-Sodium Activity Ratio in Soil Suspension with Two Ion-Selective Electrodes

A K+-selective electrode and a Na+-selective electrode were used to construct a measuring cell without liquid-junction for the determination of the ion activity ratio of K+ to Na+ in soil suspensions. The measured cell potential was not affected by the total electrolyte concentration when the total cation concentration was 10-1-10-3 mol L-1 and the concentration ratio CK+ / CNa+. was 10:1 to 1:50. When the concentration ratios were equal to 1and the total electrolyte concentrations were 10-2 and 10-3 mol L-1, the ion activity ratio measurement would not be affected by pH in the pH range of 3.5 to 11.5 and 4.4 to 11 respectively. Ions other than H+ have no remarkable influence on the measurement. The ion activity ratio of K+ to Na+ measured directly in soil suspension agree well with those in centrifuged supernant solution. The relative deviation was within 4%. From the measured ion activity ratio, the difference of the bonding energies of K+ and Na+ ions was calculated.

Preparation of CeO_2 Nanoparticles and Its Application to Ion-selective Electrodes Based on Acetyl Cellulose

CeO2 nanoparticles with an average diameter of about 30 nm were prepared by sol-gel method at lower temperature. The gel, transformed from the aqueous solution of metal nitrate and citric acid, can be combusted completely at lower temperature. The redox behavior and the crystallization process of the dried gel were studied by thermogravimetric analysis and infrared spectroscopy. The synthesized powders were characterized by X-ray powder diffraction and transmission electron microscopy. In addition, rare earth elements ion-selective electrodes based on acetyl cellulose were prepared using ultra fine cerium oxide powders.

Research on Bipolar Membrane Electrodialysis for Ion Exchange of Molecular Sieves

In view of the problems associated with large amount of discharged wastewater and serious pollution in the existing technology for removing sodium species from molecular sieves,this research work introduces the bipolar membrane electrodialysis into the process of removing sodium species from molecular sieves,and proposes a novel method of cleanly removing sodium from molecular sieves.The results show that the technology for removing sodium ions from the molecular sieves with an indirect electrodialysis process is feasible,and can recover Na OH solution.The bipolar membrane electrodialysis is especially suitable for treating the USY,ZSM-5 and Beta molecular sieves with high acid-resistance,and the physicochemical properties and catalytic performance of the prepared molecular sieves are roughly equivalent to those of the ammonium ion-exchange method.In comparison with the ammonium ion-exchange method,the process is clean and environmentally friendly,which consumes less water,and does not discharge wastewater to exhibit a rosy prospect of industrial application.

TREATMENT OF INDUSTRIAL WASTEWATER FROM AN ALUMINA PLANT BY MEMBRANE (Ⅰ) ——Measurement of Limiting Current Density of Electrodialysis

In order to design the technological process of desalination by electrodialysis for the industrial wastewater of an alumina plant, the limit current density of the industrial wastewater is measured, and the equations of limit current density, voltage drop of the unit membrane pair at the limiting current and desalination ratio at the limiting current were obtained.

Purification and Regeneration of Spent Electroless NickelPlating Baths by Electrodialysis

A method using electrodialysis to seperate phosphite from spent electroless nickel (EN) plating solution was studied. The major working parameters for the electrodialyzer with our selected membranes such as voltage, current and the flow rate of spent EN bath and condensed solution were optimized. Under the optimum operating conditions, spent EN bath could be effectively purified. And then the purified solution was replenished and reused for EN plating. The life of the EN bath was prolonged for more than 17 metal turnovers (M.T.Os). It showed that the electrodialysis method was one of the most effective means for purification and regeneration of spent EN plating baths and for saving resources and reducing waste.

Study on concentration of β-Naphthalenesulfonic acid by electrodialysis

Anion-exchange membranes 3362W and AM-203 were evaluated for facilitating the concentration of β-Naphthalenesulfonic acid by electrodialysis. The effect of concentration, temperature, electric current and time on the electrodialysis process were studied. Experimental results indicated that electrodialysis was an effective method for concentrating β-Naphthalenesulfonic acid at 25℃. Higher efficiencies were not obtained at high temperature. The overall current efficiency was 80%～95%.

Removal of Mercury(Hg(Ⅱ)) from Seaweed Extracts by Electrodialysis and Process Optimization Using Response Surface Methodology

In this work,response surface methodology(RSM)was employed to model and optimize electrodialysis process for mercury(Hg(II))removal from seaweed extracts.Box-Behnken design(BBD)was utilized to evaluate the effects and the interaction of influential variables such as operating voltage,influent flow rate,initial concentration of Hg(II)on the removal rate of Hg(II).The developed regression model for removal rate response was validated by analysis of variance,and presented a good agreement of the experimental data with the quadratic equation with high value coefficient of determination value(R2=0.9913,RAdj 2=0.9678).The optimum operating parameters were determined as 7.17V operating voltage,72.54L h−1 influent flow rate and 5.04mgL−1 initial concentration of mercury.Hg(II)removal rate of 76.45%was acquired under the optimum conditions,which showed good agreement with model-predicted(75.81%)result.The results revealed that electrodialysis can be considered as a promising strategy for removal of Hg(II)from seaweed extracts.

Construction and Application of a PVC Membrane Enoxacin Ion-selective Electrode Based on a Needle-shaped Inner Reference Electrode

A PVC membrane enoxacin ion-selective electrode based on a needle-shaped inner reference electrode was prepared. A Ag/AgCl wire was used as the substrate of this electrode. It was previously coated with a thin sheet of urea-formaldehyde resin containing Cl - ions to form a needle-shaped inner reference electrode, then the inner reference electrode was coated with a thin sheet of a PVC membrane containing an enoxacin tetraphenylborate ion-pair complex. The influences of various ion-pair complexes, concentrations of the active components in the membrane and the plasticizers on the performance of the electrode were studied by orthogonal design. The linear response range of the electrode was 7.9×10 -5 -1.0×10 -2 mol/L. The detection limit was 2.0×10 -5 mol/L. The slope was 30.4 mV/decade(25 ℃). The electrode can be used for the potentiometric determination of enoxacin tablets directly. The average recovery was 100.4%, and the RSD was 0.9%. The results agreed with those determined by the method in Chinese Pharmacopoeia.

Concentration of mixed acid by electrodialysis for the intensification of absorption process in acrylic acid production

The absorption process in acrylic acid production was water-intensive.The concentration of acrylic acid before distillation process was low,which induced to large amount of wastewater and enormous energy consumption.In this work,a new method was proposed to concentrate the side stream of absorption column and thus increase the concentration in bottom product by electrodialysis.The influence of operating conditions on concentration rate and specific energy consumption were investigated by a laboratory-scale device.When the voltage drop was 1 V·cP^(-1)(1 cP=10^(-3) Pa·s),flow velocity was 3 cm·s^(-1) and the temperature was 35℃,the concentration rates of acrylic acid and acetic acid could be 203.3%and 156.6%in the continual-ED process.Based on the experimental data,the absorption process combined with ED was simulated,in which the diluted solution from ED process was used as spray water and the concentrated solution was feed back to the absorption column.The results shown that the flow rate of spray water was decreased by 37.1%,and the acrylic acid concentration at the bottom of the tower was increased by 4.56%.The ions exchange membranes before and after use 1200 h were tested by membrane surface morphology(scanning electron microscope),membrane chemical groups(infrared spectra),ion exchange capacity,and membrane area resistance,which indicated the membrane were stable in the acid system.This method provides new method for energy conservation and emission reduction in the traditional chemical industry.

Highly Efficient Power Conversion from Salinity Gradients with Ion-Selective Polymeric Nanopores

A polymeric nanopore membrane with selective ionic transport has been proposed as a potential device to convert the chemical potential energy in salinity gradients to electrical power. However, its energy conversion efficiency and power density are often limited due to the challenge in reliably controlling the size of the nanopores with the conventional chemical etching method. Here we report that without chemical etching, polyimide （PI） membranes irradiated with GeV heavy ions have negatively charged nanopores, showing nearly perfect selectivity for cations over anions, and they can generate electrical power from salinity gradients. We further demonstrate that the power generation efficiency of the PI membrane approaches the theoretical limit, and the maximum power density reaches 130m W/m2 with a modified etching method, outperforming the previous energy conversion device that was made of polymeric nanopore membranes.

Diffusion analysis and modeling of kinetic behavior for treatment of brine water using electrodialysis process

In this study,the removal of monovalent and divalent cations,Nat,Kt,Mg2t,and Ca2t,in a diluted solution from Chott-El Jerid Lake,Tunisia,was investigated with the electrodialysis technique.The process was tested using two cation-exchange membranes:sulfonated polyether sulfone cross-linked with 10%hexamethylenediamine(HEXCl)and sulfonated polyether sulfone grafted with octylamine(S-PESOS).The commercially available membrane Nafion®was used for comparison.The results showed that Nafion®and S-PESOS membranes had similar removal behaviors,and the investigated cations were ranked in the following descending order in terms of their demineralization rates:Nat>Ca2t>Mg2t>Kt.Divalent cations were more effectively removed by HEXCl than by monovalent cations.The plots based on the WebereMorris model showed a strong linearity.This reveals that intra-particle diffusion was not the removal rate-determining step,and the removal process was controlled by two or more concurrent mechanisms.The Boyd plots did not pass through their origin,and the sole controlling step was determined by film-diffusion resistance,especially after a long period of electrodialysis.Additionally,a semi-empirical model was established to simulate the temporal variation of the treatment process,and the physical significance and values of model parameters were compared for the three membranes.The findings of this study indicate that HEXCl and S-PESOS membranes can be efficiently utilized for water softening,especially when effluents are highly loaded with calcium and magnesium ions.

DEVELOPMENT OF DOUBLE-BARRELED CALCIUM ION-SELECTIVE MICROELECTRODE

A new PVC matrix membrane double-barreled calcium ion-selective microelectrode based on liquid ion exchanger has been designed and constructed.The tip diameter of about 2.5μm as well as lower selectivity coefficients for K+,Na and Mg2+are adequate for in-tracellular measurements of Ca activities.The inner wall of the selective channel was made to be hydrophobic by treatment withalkyl-alcohols.By means of this microelectrode some physiologicalphenomena related to Ca2+activities have been studied,and Caconcentrations in clinical microsamples have also been determined.

Potentiometric Urea Biosensor Based on Ion-Selective Electrode by Different Immobilization Procedures

Enzyme was immobilized on an ammonium ion-selective electrode by different methods.An ion-selective electrode is not completely ion-specific,and interfering ions react with the ion-selective electrode membrane,altering the measured potential.Therefore,the characteristics of the effect of other ions on ammonium ion-selective electrode-based urea biosensors are considered.Based on the experimental results,the urea biosensor based on entrapment had a high response voltage of around 189 mV and fast response time of around 16 sec.Moreover,selectivity of the urea biosensor in different interfering ions was considered to elucidate the characteristics of ammonium ion-selective electrode-based biosensors.