EFFICIENT AND VERSATILE LABORATORY ELECTRODIALYSIS …

Romanian Reports in Physics 73, 802 (2021)

EFFICIENT AND VERSATILE LABORATORY ELECTRODIALYSIS DEVICE USED FOR REMOVAL OF IRON IONS FROM A SYNTHETIC

WASTEWATER

S. CĂPRĂRESCU1, V. PURCAR2*, V. RĂDIȚOIU2, C. A. NICOLAE2, C. MODROGAN3, A. A. SCARLAT3

1 “Politehnica” University of Bucharest, Faculty of Applied Chemistry and Materials Science, Inorganic Chemistry, Physical Chemistry and Electrochemistry Department,

Polizu Street No 1–7, 011061, Bucharest, Romania E-mail: [email protected]

2 The National Institute for Research & Development in Chemistry and Petrochemistry – ICECHIM, Splaiul Independentei No. 202, 060021, Bucharest, Romania

E-mails: [email protected]; [email protected]; [email protected] 3 University “Politehnica” of Bucharest, Faculty of Applied Chemistry and Materials Science,

Analytical Chemistry and Environmental Engineering Department, Polizu Street No 1–7, 011061, Bucharest, Romania

E-mails: [email protected]; [email protected]

Received August 28, 2020

Abstract. The present paper reports an efficient and versatile laboratory electrodialysis device used for removal of iron ions from a synthetic wastewater with novel polymer membrane based on chitosan (CS)-silver nitrate (Ag) solution. Our laboratory electrodialysis device was operated under potentiostatic operation mode to maintain the constant voltage of 7.5 V, for 90 minutes. The results showed that the rejection of Fe2+ was higher (> 65%) for the polymer membrane with CS-Ag solution. The physical, chemical and mechanical properties of the obtained polymer membranes were investigated by Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA) and Differential Thermal Analysis (DSC) and Optical Microscopy. FTIR spectra showed that some peaks were shifted to higher wave numbers possible due to the incorporation of CS-Ag solution in the polymer matrix. A peak that is shifting from 1435 cm–1 (polymer membrane with CS-Ag solution) to 1428 cm–1 (polymer membrane without CS-Ag solution) was attributed to vibrations of hydroxyl (–OH) functional groups from polyethylene glycol and chitosan. TGA-DSC results indicated an excellent thermal stability up to 355°C and maximum decomposition temperature over 500°C for the obtained polymer membranes. The optical microscope image confirmed that the chitosan and polyethylene glycol chains help in stabilization of the silver particles.

Key words: electrodialysis, iron ions, synthetic wastewater.

1. INTRODUCTION

The different industrial or municipal wastewaters that contain various metallic ions (e.g. iron (Fe2+), nickel (Ni2+), copper (Cu2+), cadmium (Cd2+), lead (Pb2+),

Article no. 802 S. Căprărescu et al. 2

chromium (Cr3+), mercury (Hg2+)) constitute a major risk for living systems (plants, animals, micro-organisms), public health and environmental (waters, air, soils) [1–4]. These cannot be directly or indirectly released into the environment prior to treatment because are toxic, non-biodegradable and bio-accumulative [1–5]. The excessive ingestion (1–2 mg) of these metallic ions can cause serious health problems, such as vomiting, stomach cramps, convulsions, migraine, skin irritations, pulmonary fibrosis, renal damages, cardiovascular diseases or even death [1, 3–8]. These wastewaters can come from different sources such as mining activities, smelting industries, tanneries, battery manufacture, petroleum refining, paint and pigment manufacture, agricultural applications (pesticides, insecticides, herbicides, fungicides), fertilizer industries, paper, printing and photographic industries [3, 7–9].

Many inexpensive and efficient methods such as adsorption [7–10], chemical precipitation [3, 11], ion exchange [3, 12], coagulation [13], liquid-liquid extraction [14] was extensively used for the removal of various metallic ions from different wastewater [15]. Most of these methods present some disadvantages such as incapable of removing trace levels of metallic ions from waste effluents, generate a large volume of sludge, form insoluble precipitates [6–9]. The membrane filtration technologies (e.g. ultrafiltration [5, 16], reverse osmosis [5, 16], nanofiltration [17, 18], electrodialysis [4, 19–23]) shown to be a great and feasible alternative for removal the metallic ions from industrial or municipal wastewaters. Electrodialysis is a separation process that, under the influence of an applied electric potential at electrodes, ions are transported from a concentrated solution into a raw solution using selective membrane [19–23]. The various electrodialysis systems was successfully applied for the removal and separation of different metallic ions from the municipal or industrial effluents due to many advantages, such as: high removal or separation efficiency, adaptability, does not require special maintenance and performant equipment’s, operates quietly, electrode costs are relatively low, and have lower residues [4, 19–23]. Chekioua et al. [4] used electrodialysis to remove the iron (II) ions of sulfuric acid pickling bath. Their study has demonstrated that the various parameters (current density, nature of the membrane and concentration of Fe (II)) influenced the efficiency of the electrodialysis process. Benvenuti et al. [19] applied electrodialysis in combination with ion exchange membranes (Ionac MC-3470 and Ionac MA-3475) for the treatment of nickel electroplating rinsewaters. It was reported that the electrodialysis treatment generates a very low conductivity solution and all ions detected presented adequate concentrations for water reuse. Su et al. [20] indicated that the removal of Cu2+ exceeded 99.3% with applied field strength of 1.5 V/cm and reaction time of 3 h by applied electrodialysis process with commercial ion exchange membranes (SKS-A and SKS-C). Dalla Costa et al. [21] treated a metal finishing wastewater containing different ions by electrodialysis and Nafion and Selemion membranes. The results indicated that the percent extraction of the different metallic ions from the treated solution depends on the galvanostatic or potentiostatic operation mode.

3 Electrodialysis device used for removal of iron ions Article no. 802

Many studies have reported the performance of membranes based on different biopolymers (e.g. cellulose and cellulose derivatives, chitosan, chitin) for removal of metallic ions (i.e. chromium, mercury, copper, lead) from different wastewaters [24–29]. The applications of these membranes can be justified by the abundance of these biopolymers and their advantages such as nontoxic, low cost, water-solubility, biodegradable, high hydrophilicity and biocompatibility [24, 25, 28]. Ghaee et al. [26] prepared a chitosan/cellulose acetate (CA) composite nanofiltration membrane for wastewater treatment. The studies indicated that the rejection for copper was 81.03% from a common effluent treatment plant wastewater. Miao et al. [27] an amphoteric composite nanofiltration (NF) membrane was prepared by coating the aqueous solution of sulfated chitosan (SCS) onto a poly(acrylonitrile) UF membrane. The rejection performance of SCS/PAN composite membrane for a feed solution containing sodium sulfate (1000 mg/L) was 92.1%, at 25°C, after approximately 1.7 h of treatment.

In this paper we report the synthesis, characterization and efficiency of a novel polymer membrane based on chitosan (CS)-silver nitrate (Ag) solution for removal of iron ions (Fe2+) from a synthetic wastewater using a laboratory electrodialysis device. The prepared polymer membranes were characterized using Fourier Transform Infrared (FTIR) spectroscopy, Thermogravimetric Analysis (TGA) and Differential Thermal Analysis (DSC) and Optical Microscopy.

2. MATERIAL AND METHODS

2.1. MATERIALS AND EQUIPMENT’S

Chitosan (CS) (powder, deacetylation degree ≥75%), cellulose acetate (CA) (white powder, purity 99%), polyethylene glycol 400 (PEG400) (density 1.13 g/cm3 at 20°C, viscosity 97–110 cSt (20°C)) and iron(II) sulfate heptahydrate (FeSO4 · 7H2O) were purchased from Sigma-Aldrich Chemical Co. Silver nitrate (AgNO3, 99.0%), acetic acid glacial (99–100%) and sulfuric acid (H2SO4, 95–98%) were purchased from Merck (Merck KGaA, Germany). The chemicals were weighed using a digital laboratory balance (PCB 350-3, Kern, Germany).

The prepared polymer membranes were investigated by Fourier Transform Infrared Spectroscopy (FTIR). The FTIR spectra with a wavenumber ranging from 4000 to 400 cm–1 were recorded using a Fourier infrared spectrometer (Jasco FT-IR6300) equipped with a Specac ATR GoldenGate (KRS5 lens), 32 accumulations at a resolution of 4 cm–1. The weight loss and maximum decomposition temperature for prepared polymer membranes were determined by Thermogravimetric Analysis (TGA) and Differential Thermal Analysis (DSC) using a Q5000IR (TA Instruments, USA). Each sample was heated from 35 to 740°C, at a heating rate of 10°C/min under nitrogen atmosphere (50 mL/min). The surface morphology of the prepared polymer membranes was examined with a professional optical microscope (Celestron-LCD Digital Microscope II, Full color 3.5" TFT LCD screen).


2.2. PREPARATION OF POLYMER MEMBRANES

The polymer membranes were obtained by wet-phase inversion method, at room temperature (22 ± 1°C). Initially, a chitosan (CS)-AgNO3 (Ag) solution was prepared by following procedure: chitosan (CS) (30 mg) was dissolved in 20 mL of acetic acid solution (2 · 10-4 M), heated at 50°C, at constant magnetic stirring (300 rpm) (magnetic stirrer Nahita 690/1), for 2 h. To this solution, 10 mL of AgNO3 solution (0.1 N) and 10 mL of distilled water were added, under stirring for another 2 h.

The polymer solution and membrane were prepared by following procedure: in a 500 mL beaker was mixed thoroughly a mixture of cellulose acetate (2 g), CS-Ag solution (0.25 mL) and 0.2% (wt) PEG400. Then the obtained mixture was completely dissolved in acetic acid glacial (50 mL) under continuous magnetic stirring (300 rpm), at 80°C (magnetic stirrer Nahita 690/1), for 3 h. After that, the obtained polymer solution was maintained in repose 24 h at room temperature (22 ± 1°C). Finally, the resultant homogeneous polymer solution was cast on a glass plate using a manual film applicator (Multicator 411, Erichen). The casted polymer membrane was then allowed to evaporate for one minute and then was dipped immediately into a glass vessel which contains distilled water for coagulation. The polymer membrane preparation is schematically indicated in Fig. 1. The obtained polymer membrane was washed with distilled water for three times, before used in the laboratory electrodialysis device. The thickness of spread casting solution was controlled by manually adjusting the height of the casting applicator (thickness of membrane was 0.3 mm). A similar procedure was employed for the preparation of the polymer membrane without CS-Ag solution. The small pieces (1 mm × 15 mm) were cut from both type of prepared polymer membranes (Table 2) and examined before using in the laboratory electrodialysis device.

Fig. 1 – Schematic pathways for preparation of polymer membrane with CS-Ag solution.


Table 1

Codes and thickness of polymer membranes

Sample Codes Thickness [mm]

Polymer membrane with CS-Ag solution M1 Polymer membrane without CS-Ag solution M2 0.3

2.3. LABORATORY ELECTRODIALYSIS DEVICE

Treated of a synthetic wastewater containing Fe2+ was performed in our laboratory electrodialysis device consisting in three chambers (detachable), made from carbon fiber/polyamide 6 thermoplastic composite material. Two small and thin cylinder plate electrodes (anode (A) and cathode (K)), made from pure lead (99%), were placed at the extremities of the device and connected to a DC power supply (Axiomet AX-3005D, 0÷30VDC, 0÷5A). The obtained polymer membranes were positioned between the chambers (anodic-central and central-cathodic) (Fig. 2). The thicknesses of each chamber and each lead electrode were 11.08 mm and 0.173 mm. The working areas of each lead electrode and each prepared polymer membrane were 6.43 cm2 and 15.34 cm2. The measurements were performed using a Sattiyrch digital caliper stainless steel (LCD screen, 6inch, fraction or metric units for readability).

Fig. 2 – Laboratory electrodialysis device.

The synthetic wastewater used in this study was prepared by using iron(II) sulfate heptahydrate, 15 mL of sulfuric acid (1 N) and distilled water in order to


produce a concentration solution of 0.15 g/L Fe2+. All chambers were filled with the same prepared synthetic wastewater (equal volume of approximately 17 cm3). Each experiment was carried out at room temperature (22 ± 1°C), under potentiostatic operation mode (applying an anode-cathode constant voltage of 7.5 V), for 90 minutes.

3. RESULTS AND DISCUSSIONS

3.1. LABORATORY ELECTRODIALYSIS TESTS

The Demineralization Rate DR[%] and Rejection of Fe2+ R[%] were determinate in order to evaluate the effect of the applied voltage to the laboratory electrodialysis device.

DR[%] was calculated using the following equation [19, 22]:

D [%] 1 100fin

in

R

(1)

where: λin – conductivity of the initial wastewater (mS/cm) and λfin – conductivity of the final filtrated solutions after treatment (from central compartment) [mS/cm].

The conductivity of filtrated solutions was measured using a multiparameter Consort 1010 equipped with a conductivity cell SZ10T.

R[%] was calculated using the following equation [4, 19–23, 29]:

[%] 1 100fin

in

CR

C

(2)

where: Cin – Fe2+ concentrations in the initial synthetic wastewater [g/L] and Cfin – Fe2+ concentrations in the final solution (central chamber), after 90 minutes of treatment [g/L].

The initial synthetic wastewater and the final solutions, after each electrodialysis test, were filtrated using filter paper. The small quantities from filtrate solutions were analyzed using an UV–Vis spectrophotometer (Metertech SP-830+, wavelength 510 nm) in order to determine the Fe2+concentrations.

The calculated values of DR[%] and R[%] are showed in Table 2.

Table 2

The values of DR% and R% after 90 minutes of treatment

Samples DR (%)

R (%)

M1 56.42 65.23 M2 32.62 41.11


It can be observed that the R[%] of iron ions was higher for polymer membrane with CS-Ag (65.23%) (sample M1) in comparison with polymer membrane without CS-Ag (41.11%) (sample M2), after 90 minutes of treatment. The increase of R[%] can be attributed to reduction of the protons sulphate that competes with the iron ions and due to the water dissociation under the influence of the applied electric potential [4]. The protons through by polymer membrane and move towards the lead anode, while the hydroxyl ions (HO–) through by polymer membrane and move towards to the lead cathode where meeting with the iron ions. The higher values of DR[%] and R[%] were obtained for polymer membrane with CS-Ag and can be attributed to interactions of iron ions with amino (RNH3

+) and hydroxyl groups presented in chitosan structure [28, 30]. Based on this research and other reported in literature [4, 19–21, 29], removal efficiency depends on various parameters such as: voltage or current intensity applied at electrodes, operation time, flow rate, pH of solutions, initial feed wastewater concentration, nature of the membrane. Della Costa et al. [21] used the electrodialysis to treat of wastewater containing ions of Zn (zinc), Ni (nickel), Cu (copper), Fe (iron) and Al (aluminum). The results indicated that the highest extraction (67.7%) was obtained for aluminum ions and the lowest percent extraction (16.0%) was obtained for the iron ions after 5 h of treatment. This difference can be due to the relative mobility of these coordinated ions in solution and due to the variations in volume and electrical charge.

3.2. CHARACTERIZATION OF PREPARED POLYMER MEMBRANES

The FTIR spectra of polymer membranes with and without CS-Ag solution, before the electrodialysis test, are depicted in Fig. 3.

Fig. 3 – FTIR spectra of polymer membrane with CS-Ag solution (M1) and of polymer

membrane without CS-Ag solution (M2).


FTIR spectra for both types of prepared polymer membranes shows various absorption bands in 4000–400 cm–1 domain (Fig. 3). The analysis of FTIR spectra shows the stretching vibration of OH groups involved in hydrogen bonds located at 3421 cm–1 (sample M1) and 3455 cm–1 (sample M2). The peak that appears at 2943 cm–1 (sample M1) and 2951 cm–1 (sample M2), is due to the stretching of CH2 groups (stretching vibrations) [29, 30]. The peaks shifting to higher wave numbers may be due to coordination bond between the silver and electron rich group (oxygen). This indicates that the silver is bound to the functional groups of chitosan [30]. The intense peak present in both membranes at 1736 cm–1 is due to carbonyl group. The peak at 1612 cm–1 (sample M1) corresponds to the stretching vibration of C=O. The peak shifting from 1435 cm–1 (sample M1) to 1428 cm–1 (sample M2) is attributed to vibrations of hydroxyl (–OH) functional groups from polyethylene glycol and chitosan and corresponding to CH2OH groups. The peak that appears in both types of polymer membranes at 1367 cm–1 may be due to CH3 symmetric deformation vibration. The peak observed at 1032 cm–1 is shifted to higher wave number (1034 cm–1) which can be due to C-O-C from polyethylene glycol chains (stretching vibrations) [29–31].

The characteristic TGA-DSC curves for prepared polymer membranes are showed in Fig. 4.

Fig. 4 – TGA-DSC curves for polymer membrane with CS-Ag solution (M1) and for polymer



Table 3

The values of the weight loss (Wt. loss) and maximum decomposition temperature (Tmax) for prepared polymer membranes

35–98°C 98–201°C 202–275°C 275–425°C 425–740°C R*

Wt. loss

Wt. loss Tmax

Wt. loss Tmax

Wt. loss Tmax

Wt. loss Tmax 740°C Sample

% % °C % °C % °C % °C % M1 1.89 2.30 194.7 5.20 245.4 73.34 358.2 15.28 500.2 1.99 M2 2.89 1.44 181.3 3.72 231.3 76.47 359.6 15.37 583.2 0.11

R* – residue Figure 4 illustrates the TGA-DSC curves of the prepared polymer membranes.

It can be observed that the both types of polymer membranes show good thermal stability up to 355°C and Tmax occur over 500°C (Fig. 4 and Table 3). In the present investigation, the weight loss of 1.89% (sample M1) and of 2.89% (sample M2), in the interval of 35–98°C, corresponds to water evaporation [29–35]. The weight loss of 5.20% (sample M1) and of 3.20% (sample M2), from 202–275°C, may be due to the decomposition of cellulose acetate. The difference of the weight loss between 275 and 425°C can be attributed to the decomposition of chitosan [29, 33–34]. The difference in the residual mass at 740°C can be attributed to the presence of silver nitrate in the polymer matrix. The residue (at 740°C) of the sample M1 increases when the CS-Ag solution was added in the polymer matrix. This fact can be due to the interaction between the amino groups and hydroxyl groups of the chitosan and cellulose acetate [29–35]. Ahamed et al. [35] study the composites containing regenerated cellulose (RC) and chitosan (Ch) impregnated with silver nanoparticles (Ag). They indicated that the RC–Ch–Ag bio composite exhibits decreased melting temperature at 78.92°C.

The top surface morphology images of both prepared polymer membranes were observed by optical microscopy (magnification 100×) and shown in Fig. 5.

Fig. 5 – Optical micrographs for polymer membrane with CS-Ag solution (M1) and for polymer



It can be seen from Fig. 5 that the sample M1 show a homogeneous, compact and flat surface with small pores possible due to the presence of CS-Ag solution in the polymer composition in comparison with sample M2 that present many and large pores and more spherical macro-voids [29–36]. It was reported that the chitosan helps in nucleation and stabilization of the silver particles formed by with means of polyethylene glycol chains and thus, favors the distribution of silver particles [33, 36]. The optical micrograph of the polymer membrane with CS-Ag solution (M1) shows that the silver spherical particles are relatively uniformly distributed in the membrane in comparison with the polymer membrane without CS-Ag solution (M2) where these silver particles are completely absent [30–35].

4. CONCLUSIONS

Our laboratory electrodialysis devise and obtained polymer membrane based on chitosan (CS)-silver nitrate (Ag) solution was successfully applied for removal of Fe2+ from a synthetic wastewater. The results indicated that the rejection of Fe2+ was higher for polymer membrane with CS-Ag (65.23%) in comparison with polymer membrane without CS-Ag (41.11%), after 90 minutes of treatment.

FTIR spectra showed that some peaks were shifted to higher wave numbers possible due to the incorporation of CS-Ag solution in the polymer matrix. TGA-DSC confirmed that the polymer membranes have an excellent thermal stability up to 355°C and maximum decomposition temperature occur over 500°C. The optical microscope image revealed that the chitosan and polyethylene glycol chains help in stabilization of the silver particles. The presence of CS-Ag solution in the polymer membrane reduces the pore size.

The present study demonstrated that the prepared polymer membranes with CS-Ag solution can be effectively used as a low cost and efficient polymer material, using a very efficient and versatile laboratory electrodialysis device.

Acknowledgments. The work has been funded by the University POLITEHNICA of Bucharest, through the UPB-GEX2016, project no. 62/2016 and supported by a grant of the Romanian Minister of Research and Innovation, PCCDI – UEFISCDI, project no. PN-III-P1–1.2-PCCDI-2017-0428, within PNCDI III (no.40PCCDI/2018, PC4-FOTOMAH).

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