New Iminodiacetate Chelating Resin-Functionalized Fe3O4

Article pubs.acs.org/jced

Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX

New Iminodiacetate Chelating Resin-Functionalized Fe3O4 Nanoparticles: Synthesis, Characterization, and Application for the Removal of Some Noxious Metal Ions from Wastewater Salah M. El-Bahy* Chemistry Department, Turabah University College, Turabah, Taif University, Taif, 26571, Saudi Arabia ABSTRACT: A new type of magnetic chelating resin (MIDA) beads bearing iminodiacetate groups derived from acrylamide−N,N′-methylenebis(acrylamide) copolymer was synthesized in the presence of Fe3O4 nanoparticles and tested for the removal of Cu(II), Pb(II), Zn(II), and Cd(II) from aqueous solution. The prepared Fe3O4 nanoparticles were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM)-energy dispersive X-ray, transmission elelctron microscopy, and X-ray diffraction (XRD). The obtained MIDA was characterized by FTIR, SEM, Brunauer−Emmett−Teller analysis, XRD, thermal analysis, and water regain (W%). Different factors affecting the adsorption process such as pH of solution, initial concentration of the metal ions, shaking time, and temperature of solution, were investigated by batch technique. The maximum adsorption capacities were 4.1, 3.6, 2.4, and 2.2 mmol·g−1 for Cu(II), Pb(II), Zn(II), and Cd(II), respectively. Langmuir isotherm and pseudo-second-order equation could adequately describe the adsorption process of all metal ions. Thermodynamic parameters revealed that the adsorption process is endothermic, spontaneous in nature, and entropy driven. Additionally, the removal of Cu(II) was tested using the fixed-bed column technique. The effect of significant column parameters such as bed height, flow rate, and Cu(II) concentration on the performance of the column were examined. The breakthrough curves obtained were analyzed by Thomas and Yoon−Nelson kinetic models. The regeneration of the exhausted column bed was conducted with 0.1 M HNO3 solution, and MIDA was found to maintain its high adsorption capacity up to six cycles.

1. INTRODUCTION Heavy metal pollution of the surrounding environment, especially in water, has now become an epidemic problem to the environment and living organisms.1 Heavy metals are generally elements that possess atomic masses between 63.5 and 200.6 and that have a specific gravity of more than 5.0.2 The main heavy toxic metal ions in wastewater are Hg, Cu, Zn, Mn, Cd, and Pb.1,2 These kinds of heavy metals have toxicity potential and can lead to carcinogenicity in the living organisms.1−3 The quick development of industries causes the production of a large amount of waste which contains toxic heavy metals ions. Wastewaters come from many different industries such as chemical, plating, petroleum refining, and mining, burning of fossil fuels, tanneries, and paint manufacture.4 Industrial wastewater containing toxic ions are directly or indirectly discharged into the water resources mainly in the developing countries. Various techniques have been used for getting rid of these ions from wastewater, such as membrane separation, chemical reduction, chemical precipitation, ion exchange, adsorption, and biological treatment.4,5 Growing attention has recently given to chelating resins because they are simple, work well, durable, separated easily, and possess higher metal ion sorption capacities and selectivity.6−12 The removal of metal ions can be achieved by using chelating resins © XXXX American Chemical Society

containing functional groups such as amino, amidoxime, carbamate, and iminoacetate which have chelating ability toward divalent metal ions.7−18 Chelating resins with an iminodiacetate functional group such as Amberlite IRC 718, Wafatit MC 50, Lewatit TP 207, Chelex 100, Diaion CR-10, and Purolite S930 were commercially used because of their lower manufacturing costs, higher capacity, and excellent selectivity.15−17 Chelating resins with iminodiacetate functional groups were prepared to remove hazardous metal ions from wastewater containing metal ions such as copper, cadmium, nickel, lead, manganese, mercury, and zinc due to their high selectivity.12−18 In our earlier works, a chelating resin with iminodiacetate groups was synthesized through subsequent treatment of cross-linked polyacrylamide by ethylenediamine and sodium chloroacetate.12 The prepared resin was studied for efficient adsorption of some metal ions such as lead, cadmium, manganese, and zinc.12 Also, in our recent research project, a new iminodiacetate chelating resin derived from polyacrylonitrile was synthesized for sorption of toxic metal ions from contaminated water.18 Recently, adsorbents containing magReceived: March 25, 2018 Accepted: May 8, 2018

A

DOI: 10.1021/acs.jced.8b00241 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

a magnetic bar. The precipitate was washed with boiled water followed by decantation until the pH is below 7.5. Finally, the precipitate was dried in air and stored in a glass vial for characterization and further cross-linking studies. 2.3. Preparation of the Magnetic Chelating Resin. 2.3.1. Synthesis of Magnetic Cross-Linked Polyacrylamide (MPAM). Magnetic cross-linked polyacrylamide beads were synthesized by the suspension polymerization method. The mixture containing the monomers (9.5 g acrylamide and 0.5 g N,N′-methylenebis(acrylamide)) in the presence of magnetite (5 g Fe3O4) were suspended into a mixture of toluene (50 mL) and chlorobenzene (50 mL). The reaction mixture was heated in the warm water bath at 60 °C and stirred until the monomers became homogeneous. Afterward, an amount of 0.2 g (APS) was added in the above system, and the mixture was stirred at 80 °C for 30 min. After reaction, the mixture temperature was allowed to decrease. Afterward, the obtained magnetic resin (MPAM) was separated by external magnet, washed with excess deionized water and acetone, and finally dried in air and sieved. 2.3.2. Synthesis of Magnetic Cross-Linked Polyvinylamine (MPVA). MPAM beads (4 g) were swollen in solution of sodium hydroxide (80 mL, 2.0 M) for 5 min. Antiform (120 mL, 1.0 M NaClO) was added, and the mixture was allowed to react in an ice-water bath for 72 h. Subsequently, the obtained magnetic polyvinylamine resin (MPVA) was separated by external magnet and washed with deionized water followed by acetone washing. The amine value of MPVA resin was calculated according to the reported volumetric method.10 A 50 mL aliquot of HCl solution (0.05M) was added to MPVA resin (0.3 g) and conditioned for 12 h on a Vibromatic-384 Shaker, Gallenkamb, England. The remaining concentration of HCl was calculated by titration with NaOH solution (0.05 M) and phenolphthalein as indicator. The amino group concentration (mmol g−1) was estimated from eq 1.

netic nanoparticles is one of the capable techniques projected because of its ease of application and fast separation in recovering sorbent from solution with external magnetic field.19−21 Many kinds of magnetic nanoparticles are used including magnetite, maghemite, and magnetic graphene nanoparticles.22−25 Magnetic nanoparticles have received significant consideration because of their exclusive properties that make them extremely valuable in many fields. The magnetic nanoparticles (generally diameter less than 20 nm) show no magnetic behavior and consequently the particles do not attract each other, offering a benefit of reducing risk of nanoparticles aggregation and a possibility to be used for preparing magnetic adsorbents.21,23 The application of a sorption technique depends on the use of magnetic adsorbents including use in the subsequent stages: (a) sorption of metal ions, (b) magnetic separation of the sorbent from solution containing metal ions, (c) recovery and regeneration of adsorbent, and (d) management of the regeneration solution and the sorbent. The magnetic adsorbents were reported to show greater sorption capacity more than adsorbents without magnetic properties.7,26−28 Finally, the use of these adsorbents for sorption of toxic ions from aqueous solution media has been reported.28−34 The purpose of this study is to synthesize, characterize and apply the magnetic chelating resin containing iminodiacetate groups for the uptake of some metal ions such as Cu(II), Pb(II), Zn(II), and Cd(II) from aqueous medium by batch and column techniques. The effects of many parameters that affect the removal of ions including pH of solution, initial metal ions concentration, shaking time, and temperature will be investigated by batch system. Sorption isotherms and thermodynamic and kinetic properties of metal ions uptake will be also examined. Breakthrough curves for sorption of the metals under study will be presented by the column system as well. The effects of design factors on the shape of the breakthrough curve will be studied, including flow rate, concentration of metal ions and bed depth. The dynamics of the adsorption process will be modeled by Thomas model and Yoon−Nelson model. These kinetic models will be used to investigate the breakthrough curves and to determine the characteristic factors of the column that are helpful for process design at a real scale. The robustness of the magnetic chelating resin will be examined by the column system.

concentration of amino group =

(M1 − M 2)50 0.3

(1)

where M1 and M2 are the initial and final concentrations of HCl, respectively. A total amine value of MPVA was calculated as 5.2 mmol g−1. 2.3.3. Synthesis of Magnetic Iminodiacetate Chelating Resin (MIDA). A mixture of sodium monochloroacetate (30 g) in 200 mL of deionized water and 2 g MPVA resin was heated at 75−80 °C for 72 h in the presence of sodium iodide as catalyst. The magnetic chelating resin (MIDA) was separated from aqueous solution by external magnetic field, washed with deionized water followed by acetone, and finally air-dried. 2.4. Characterization of the Resins. The FTIR spectra of the samples were measured by Nicolet 380 Fourier transform infrared spectrometer (400−4000 cm−1) in KBr phase. The chemical structure and morphology of the prepared samples were analyzed by SEM-EDX using SEM model FEI Quanta 250 FEG microscope connected with energy dispersive X-ray spectrometry (EDX). The particle size and morphology of the Fe3O4 nanoparticles was studied by JEOL JEM 2100 transmission electron microscope (TEM) with an accelerating voltage of 160 Kv. Brunauere−Emmette−Teller (BET) method was studied to determine the specific surface area of magnetic chelating resin (MIDA). BET was measured by the nitrogen sorption and desorption isotherm using NOVA 3200 automated gas adsorption system (Quantachrome, USA) at

2. MATERIALS AND METHODS 2.1. Materials. Acrylamide (AM), N,N′-methylenebis(acrylamide) (MBA), was used as pure grade products of Merck Co. (W.Germany). Ammonium persulfate (APS), sodium hydroxide, ammonium hydroxide, sodium hypochlorite, sodium carbonate, chloroacetic acid, and nitric acid were purchased from Sigma-Aldrich, USA. Metal salts FeCl3·6H2O, FeSO4·7H2O, (CuNO3)2, Pb(NO3)2, Zn(NO3)2 ·6H2O, Cd(NO3)2·4H2O, and other reagents were of analytical reagent grade. 2.2. Synthesis of Fe3O4 Nanoparticles. Fe3O4 nanoparticles were synthesized by the coprecipitation method.35 FeCl3·6H2O (2.7 g, 10 mmol) and FeSO4·7H2O (1.39 g, 5 mmol) were dissolved in 25 mL of deionized water containing HCl (5 mmol) to form a homogeneous solution, and the mixture was stirred for 30 min at 60 °C. NH4OH (100 mL, 30%) was poured into the synthesized Fe(III)/Fe(II) until a black precipitate crystallized, for 40 min with continuous stirring. The formed black precipitate (Fe3O4) was collected by B



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−196 °C. The crystalline structure and phase composition of the prepared samples were performed by X-ray diffractometer (XRD, PANalytical’s X’Pert PRO MRD) with Cu Kα radiation (wavelength = 154.056 pm) and scanning rate of 2° in 2θ/min. Thermal analysis was measured on magnetic chelating resin using SDT Q600 V20.5 Build 15 (Universal V4.5A TA Instruments), USA. The selected experiment conditions were performed with 9.59 mg of the resin under nitrogen atmosphere. The magnetic chelating resin was heated from room temperature to 700 °C at 10 °C/min. The water regain factor (W %) is defined as the amount of water held intrinsically by one gram of dry adsorbent. The value of water regain was calculated according to the earlier published method:11 1.0 g of swollen adsorbent sample was packed in a glass column and centrifuged to remove excess water at 3000 rpm for 5 min. The magnetic chelating resin was weighed before (Ww) and after complete dryness at 75 °C for 48 h and cooling (Wd). Equation 2 was used to calculate the water regain.11 (Ww − Wd) W% = 100 Ww

internal diameter of 1.0 cm. The prepared magnetic chelating resin was packed in the column in a water suspension. A solution containing metal ions with known concentration under the optimum pH value was pumped in the downward direction using a peristaltic flow rate pump at a fixed flow rate to the column. The samples of effluent were taken at different time intervals and analyzed until the outlet concentration of metal ions was equal to the inlet concentration. The effects of different process parameters, namely, bed depth, concentration, and flow rates were examined. All the sorption experiments were performed in triplicate, and the average value was taken. 2.6.2. Column Data Analysis. Fixed-bed column performance was conducted through a break-through curve which is obtained by plotting Ceff/Co on the vertical axis and time (t) on the horizontal axis, where Ceff and Co are effluent and influent metal ion concentration (mmol L−1), respectively. The effluent volume (Veff) was calculated by eq 4 with the following equation. Veff = Ft total

where F and ttotal are the volumetric flow rate (mL min ) and the total flow time (min) of the solution containing metal ions, respectively. The total amount of metal ions (Mads, mmol) in the fixed bed column36 is given by eq 5.

(2)

where Ww and Wd represents weights (g) of the swollen and dried magnetic chelating resin, respectively. 2.5. Batch Adsorption Studies. Batch studies were conducted by shaking 0.1 g of resins (raw chelating resin or magnetic chelating resin) with 100 mL of metal ions solution using a temperature controlled shaker at 250 rpm. The pH of the aqueous solutions was controlled by 0.1 M HNO3 or 0.1 M NaOH using the Orion 900S2 model pH meter. The mixture was shaken for a certain period at room temperature (25 °C) unless specified. Subsequently, the chelating resins (raw resin or magnetic resin) were filtered, and the concentration of metal ions in the filtrate was measured by ICP-OES spectrometer. All adsorption experiments were repeated at least three times to check the reproducibility of the obtained results. Metal ions adsorption capacity q (mmol g−1) was determined using eq 3. q=

(Co − Ce)V W

(4) −1

Mads =

FA F = 1000 1000

t = t total

∫t =0

(Cads) d t

(5)

where A (mmol min mL−1) is the area under the time− concentration break-through curve which is obtained by integrating Cad (Cad = Co − Ceff) vs t (min). The total amount of metal ions mtotal (mmol)36 was determined as follow.

mtotal =

CoFt total 1000

(6) −1 36

The equilibrium adsorption capacity (qe (exp)) (mmol g ) was calculated using eq 7. qe(exp) =

(3)

−1

Mads W

(7)

where W is the weight of magnetic chelating resin. The equilibrium concentration of metal ions, Ce (mmol L−1) was determined by eq 8.

where q (mmol g ) is the adsorption capacity at equilibrium; Co (mmol L−1) and Ce (mmol L−1) are the initial and the equilibrated metal ion concentrations, respectively; V (L) is the volume of solution in liter and W (g) is the mass of dry magnetic chelating resin. To estimate the effect of pH, adsorption experiments were operated at different pH values in a range of 1−6 by shaking the solution containing single-metal ion ((100 mL, 5 mmol L−1) with 0.1 g adsorbent. To assess the adsorption isotherms, adsorption experiments were conducted by varying initial metal concentration in the range 1.0−20 mmol L−1 at optimum pH. Sorption kinetics were performed by shaking 0.1 g of magnetic resin with 100 mL of metal ion solution at maximum adsorption concentration and optimum pH. Samples (volume of 1.0 mL) were regularly collected, and metal ion concentration was measured. The effect of temperature was investigated under different temperatures of 25, 35, 45, and 55 °C, optimum pH, and concentration of 1.0 mmol L−1 of metal ions. 2.6. Column Adsorption Studies. 2.6.1. Column Adsorption. The fixed-bed column experiment was conducted at 25 °C in a glass column having a length of 10 cm and an

Ce =

mtotal − Mads 1000 Veff

(8)

The total percentage removal R (%) of Hg(II) is given by eq 9.37

R(%) =

Mads 100 mtotal

(9) 36

The mass transfer zone (Δt) Δt = te − tb

was presented by eq 10. (10)

where te represents the bed exhaustion time and tb is the breakthrough time. The length of mass transfer zone Zm36 can be calculated using eq 11. ⎛ t ⎞ Z m = Z ⎜1 − b ⎟ te ⎠ ⎝ C

(11) DOI: 10.1021/acs.jced.8b00241 J. Chem. Eng. Data XXXX, XXX, XXX−XXX


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Figure 1. Schematic design of the preparation process of (1) MPAM, (2) MPVA, and (3) MIDA.

where Z is the bed height (cm). 2.6.3. Column Regeneration. Regeneration of MIDA resin for multiple uses is its important characteristic. In this work Cu(II) was eluted on the magnetic resin with 70 mL of 0.1 M HNO3 at constant flow rate of 1 mL min−1. After each cycle of sorption−desorption process, the magnetic resin was then washed with excess deionized water and sodium hydroxide, respectively. The regenerated resin now is ready for the next adsorption cycle using the experimental conditions of initial concentration = 5 mmol L−1, pH = 5.5, flow rate = 1 mL min−1 and bed height = 2.2 cm. To estimate the reusability of magnetic chelating resin the elution of the metal ions was operated for six cycles.

MPVA, and MIDA. The IR spectrum of pure Fe3O4 (Figure 2a) showed the characteristic vibration bands under 1000 cm−1, generally there are two peaks in ferrites, at 440 and 456 cm−1, which are related to Fe−O stretching vibrations of Fe3O4.24 But the broad peaks present at around 3140 and 1628 cm−1 corresponded to the hydroxyl stretching and the hydroxyl bending vibrations of adsorbed water on the surface of porous Fe3O4, respectively.25 Additionally, the peak at 1110 cm −1 may be attributed to the SO42− stretching vibration of unreacted FeSO4.25 All the previous vibration bands of Fe3O4 are observed in the spectrum of MPAM, MPVA, and MIDA (Figure 2b−d), suggesting that magnetite (Fe3O4) nanoparticles have been successfully encapsulated in the prepared resins. The IR spectrum of MPAM (Figure 2b) showed the characteristic absorption of the amide (N−H) group at 3185 and 3298 cm−1, and the peaks at 1640 and 1594 cm−1 associated with the stretching vibration of (CO) and (C− N), respectively.22 The IR spectrum of MPVA (Figure 2c) showed the intensity of the (CO) peak (1640 cm−1) decreased, which confirms that the amide groups in MPAM have been converted to amine groups by the Hofmann degradation reaction, exhibiting the characteristic absorption band of the amine (NH2) group at 3305 cm−1. The IR spectrum of MIDA (Figure 2d) showed the new absorption peak at 1714 cm−1 assigned to CO in −COOH.14 Moreover, the new small bands at 1399 and 1440 cm−1 attributed to carboxylic groups were present in the spectrum of MIDA.12,18 The surface morphology of the prepared magnetite nanoparticles was examined using a scanning electron microscopic (SEM) with 80 000 magnification. The images are shown in Figure 3a. It is evident from the images that the magnetite particles are at nanoscale. The EDX peaks (Figure 3b) indicate the exact iron percent in Fe3O4. No other signal was detected within the detection limits of EDX which confirms the purity of the Fe3O4 nanoparticles. As indicated in (Figure 3c) magnetite nanoparticles obtained from a TEM micrograph show a homogeneous spherical shape with a diameter of about 17− 20 nm. The surface morphology of the MIDA was examined by SEM (Figure 3d). Irregular surface and various pores in the

3. RESULTS AND DISCUSSION 3.1. Characterization of the Prepared Samples. The design of the synthesized magnetic resins is shown in Figure1. Figure 2 shows the FTIR spectra of pure Fe3O4, MPAM,

Figure 2. IR spectra of (a)Fe3O4, (b) MPAM, (c) MPVA, and (d) MIDA. D



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Figure 3. (a) SEM image of Fe3O4; (b) EDX of Fe3O4; (c) TEM image of Fe3O nanoparticles and (d) SEM image of MIDA chelating resin.

considered as mesoporous structure.36 It increases the movement of cation to the internal adsorption sites. XRD patterns of pure Fe3O4 are shown in (Figure 5a) and peaks were observed at 30.4°, 35.7°, 43.4°, 53.9°, and 57.4° corresponding to planes 220, 311, 400, 422, and 511. The diffraction peaks of the prepared magnetite nanoparticles matched with the JCPDS card number 11-0614 of magnetite. The crystal size (d) of magnetite nanoparticle can be determined by using the Scherrer equation (eq 12) as

resin surface could be observed. We can conclude that the MIDA chelating resin presents a satisfactory morphology for uptake of the metal ions. The thermal analysis of raw chelating resin (IDA) and magnetic chelating resin (MIDA) was measured by thermogravimetric analysis (TGA). TGA analysis (Figure 4a,b) displays four main steps of weight loss in IDA and MIDA. In IDA (Figure 4a) the first step below 124 °C with weight loss of 11.74% is due to the evaporation of physically adsorbed water, which exists in the external surface and interior pores of the IDA resin. The second stage below 245 °C with a weight loss of 17.64% is principally attributed to decarboxylation and anhydride formation. The third stage below 393 °C with a weight loss of 39.8% is principally due to degradation of the corresponding anhydride. The fourth stage below 700 °C with weight loss of 23.46% is due to the decomposition of the residual polyacrylamide chains. In MIDA (Figure 4b), the above stated steps were shifted to higher temperature values at 207, 389, and 509 °C instead of 124, 245, and 393 °C for the same former assignments, respectively. The average mass content of Fe3O4 on MIDA was calculated to be about 38%. The specific surface area and porosity of the prepared MIDA chelating resin were determined using the N2 sorptometer. The Brunauer, Emmett, and Teller (BET) surface area of MIDA was calculated to be 91 m2/g with total pore volume of 0.182 cm3/ g. The average pore radius was measured to be 12.2 Å, and is

d=

Kλ β cos θ

(12)

where d is the apparent crystal size (nm), K is the shape factor, λ is the wavelength of radiation (nm), β is the width at halfmaximum of the strongest peak (3 1 1) (radian), and θ is the Bragg’s angle (radian). The crystallite size of magnetite was calculated to be 18.5 nm, which was in agreement with the results measured from TEM. With the introduction of Fe3O4, cross-linked magnetic MIDA chelating resin showed the same diffraction peaks of Fe3O4 (Figure 5b). Hence Fe3O4 is immobilized into cross-linked magnetic MIDA and retained the intrinsic phase of magnetite. The water regain (W%) value for MIDA was calculated to be 26.6 mmolg−1 (wt % = 48). This value indicates the hydrophilic nature of MIDA. E



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Figure 4. Thermal analysis of (a) IDA chelating resin; (b) MIDA chelating resin.

Figure 5. Power X-ray diffraction (XRD) patterns of (a) Fe3O4 and (b) MIDA chelating resin. F



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Figure 6. Effect of pH on adsorption of Cu(II), Pb(II), Zn(II), and Cd(II) ions using MIDA.

3.2. Batch Equilibrium Studies. 3.2.1. Effect of Solution pH. The pH of aqueous media is the most significant variable affecting metal ions adsorption. For the reason that (H+) is strongly competing with metal ions in solution. The adsorption process was done by the batch technique at 25 °C in the pH range of 1.0−6.0. To avoid the hydrolysis and precipitation of metal ions as metal hydroxide, more basic solutions were not studied. As shown in Figure 6, MIDA exhibited low affinity for Cu(II), Pb(II), Zn(II), and Cd(II) at lower pH due to complete protonation of nitrogen atoms, and also carboxylic groups are not simply dissociated in low pH environment, therefore the active sites of MIDA are less accessible for metal ions due to repulsive force. Additionally, the inhibition of metal ion adsorption (adsorption capacity = zero) at pH = 1.0 has been previously reported.12,16,18 Also, no adsorption at pH of 1 reflects that the MIDA chelating resin could be regenerated using strong acid (0.1 M HNO3) as eluent. With rising of the solution pH, the protons in aqueous solution decreased, and accordingly the protonation degree of nitrogen atoms is decreased, and the dissociation degree of carboxyl active groups is increased which increases the chelation with metal ions. Here, the optimum pH value for adsorption process appeared to be about 5.5 for Cu (II) and Pb(II) and 6 for Zn(II) and Cd(II). Consequently, in this study all the subsequent experiments were performed at these optimum pH values. The adsorption capacities of magnetic chelating resin (MIDA) were compared with magnetic free one (IDA) at optimum pH and 25 °C (Table.1). It is observed that for all metal ions under investigation the sorption capacities of the iminodiacetate magnetic chelating resin (MIDA) exceeds that of the magnetite free one. This could be due to the increase in

the active site concentration of the magnetic chelating resin (MIDA) through formation of starched resin film over Fe3O4 nanoparticles which gives higher exposed active sites for chelation with M2+. 3.2.2. Influence of Initial Concentration. The influence of initial concentration of metal ions on the adsorption behavior of MIDA was examined by varying metal ions concentration between 1.0 to 20 mmol L−1 at 25 °C, and the optimum pH value is presented in Figure 7. As expected, the adsorption

Figure 7. Adsorption isotherms of Cu(II), Pb(II), Zn(II), and Cd(II) ions using MIDA.

Table 1. Equilibrium adsorption capacities of IDA and MIDA towards Cu(II), Pb(II), Zn(II) and Cd(II), 100 mL (5 mmolL−1), optimum pH and 25 °C

capacities increase as the initial Cu(II), Pb(II), Zn(II), and Cd(II) concentrations were increased. As presented in Figure 7 and Table2, the maximum adsorption capacities of Cu(II), Pb(II), Zn(II), and Cd(II) reached 4.1, 3.6, 2.4, and 2.2 (mmol g−1) at initial concentration of 17, 15, 12, and 12 (mmol L−1), respectively. The maximum adsorption capacity of MIDA toward metal ions follows the order Cu(II) > Pb(II) > Zn(II) > Cd(II). This order is similar to other adsorbents modified with iminodiacetic (IDA) groups.6,13,16,17 This order can be explained by the stability constant (K) of IDA−metal ions

equilibrium adsorption capacity (mmol g−1) metal ion

IDA

MIDA

Cu(II) Pb(II) Zn(II) Cd(II)

1.4 1.2 0.95 0.75

2.5 1.9 1.5 1.3 G



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Table 2. Comparison of Maximum Uptake with Some Other Adsorbents Reported in Literature for the Uptake of Cu(II), Pb(II), Zn(II), and Cd(II) adsorption capacity (mmol g−1) adsorbents

Cu(II)

Pb(II)

Zn(II)

Cd(II)

pH

T (°C)

ref

ASA−PGMA/SiO [CEL + DB18C6] iminodiacetic acid (IDA) chelating resin magnetic iminodiacetate resin iminodiacetate chelating resin (CR-10) iminodiacetate chelating resin (CR-15) AAM/MBA iminodiacetate ID301 NJC-702 iminodiacetate chelating resin IRC748 iminodiacetate chelating resin NDC702 CPN-IDA chelating resin M10-PVBC-C MIDA

0.42 3.02 2.27

0.31

0.4 2.87

0.35 1.75 0.65 2 0.81 0.99 1.77 2.66 0.65 0.8 0.82 1.93

5 6 5 6−6.6 5.5 5.5 5.6−6.2 5 5 5 5 5.4−4.6 5.5 5.5−6

35 25 30 25 20 20 25 20 25 30 30 25

1 4 6 7 8 8 12 13 16 17 17 18 29 this work

4.48 2.27 1.81 2.04 2.43 0.96 4.1

1.27 2.3 0.69 0.51 1.7 2.99 1.3 1.18 1.28 1.45

1.65

1.5

1.02 2.4

3.6

2.2

25

Table 3. Parameters of Langmuir, Freundlich, Temkin, and D-R Isotherms for Adsorption of Cu(II), Pb(II), Zn(II), and Cd(II) model

parameter

Cu(II)

Pb(II)

Zn(II)

Cd(II)

Langmuir isotherm

Qmax (mmol g−1) K (L mmol−1) RL R2 N Kf (mmol g−1) R2 KT (L g−1) B (J mol−1) R2 Qmax (mmol g−1) KDR (mol2 K J−2) E(kJ mol−1) R2

4.3 0.947 0.05−0.51 0.992 0.28 2 0.969 37.7 0.64 0.975 3.5 4 × 10−8 3536 0.894

4.13 0.47 0.01−0.17 0.993 0.43 1.28 0.987 6.42 0.807 0.989 2.94 1 × 10−7 2237 0.856

2.72 0.577 0.10−0.63 0.991 0.38 1.01 0.966 7.69 0.529 0.985 2.07 1.5 × 10−7 1828 0.916

2.9 0.243 0.21−0.80 0.995 0.56 0.57 0.988 2.71 0.61 0.986 1.72 3 × 10−7 1291 0.876

Freundlich isotherm

Temkin isotherm

D-R isotherm

An additional analysis of the Langmuir equation can be expressed in term of dimensionless constant (RL). The RL value was calculated using eq 14

complex. The pK values of metal−IDA chelates with Cu(II), Pb(II), Zn(II), and Cd(II) are 10.6, 7.45, 7.03, and 5.7, respectively.38 A comparison of the maximum adsorption capacities of Cu(II), Pb(II), Zn(II), and Cd(II) onto different types of sorbents is presented in Table 2. It appears that MIDA exhibited very strong adsorption ability toward metal ions. 3.2.2.1. Study on Adsorption Isotherm. The adsorption isotherm is a helpful tool to explain the interactive behaviors between the metal ions and chelating resin and clarify the properties and affinity of the chelating resin. Langmuir, Freundlich, Temkin, and Dubinin−Radushkevich(D-R) adsorption isotherm models are applied to analyze the adsorption equilibrium data. The Langmuir model is generally used to illustrate monolayer adsorption and is expressed by eq 13.39 Ce Ce 1 = + q Q max KQ max

RL =

1 1 + KCo

(14)

The RL value of RL > 1 represents unfavorable adsorption, RL = 1 represents linear adsorption, RL = 0 represents irreversible adsorption while 0 < RL< 1 denotes favorable adsorption. The Freundlich isotherm model is usually used to describe sorption at the multilayer and on heterogeneous surfaces.40 The linearized isotherm equation can be expressed using eq 15. log q = N log Ce + log KF

(15)

where KF (mmol g−1) represents the Freundlich constants and N is a measurement of adsorption. The value of N in the Freundlich model represents a favorable adsorption when (0 < N < 1). The Temkin adsorption isotherm model expects that the heat of adsorption decreases with the coverage because of adsorbate−adsorbent interaction. The Temkin isotherm model41 was mathematically described by eq 16.

(13)

where q (mmol g−1) represents the equilibrium adsorption capacity, Qmax (mmol g−1) is the maximum adsorption, Ce (mmol L−1) is the metal ion concentration in solution after equilibrium, K (L mmol−1) is the Langmuir constant related to energy of adsorption.

q = B ln KT + B ln Ce H

(16) DOI: 10.1021/acs.jced.8b00241 J. Chem. Eng. Data XXXX, XXX, XXX−XXX


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where B (J mol−1) attributed to heat of adsorption and KT (L g−1) is attributed to the maximum binding energy. The Dubinin−Radushkevich (D-R) isotherm model42 was utilized for understanding this type of adsorption, physical or chemical. The linearized form of the isotherm is given by eq 17. ln qe = ln Q max − KDR ε 2 2

(17)

−2

where KRD (mol kJ ) is a constant which is related to the mean free energy of adsorption and ε (J mol−1) represents the Polanyi potential which is related to the equilibrium concentration (Ce) as presented in eq 18.

⎛ 1⎞ ε = RT ln⎜1 + ⎟ Ce ⎠ ⎝ −1

(18) −1

where R (8.314 J K mol ) is the universal gas constant and T is the absolute temperature in Kelvin scale. The apparent free energy of adsorption E = (2KDR)−0.5 was calculated using KDR. The value of E is very important in predicting the type of adsorption. The adsorption of metal ions is said to be physical adsorption when 1 < E < 8 kJ mol−1, chemical adsorption when E > 8 kJ mol−1.43 The different parameters determined from the Langmuir, Freundlich, Temkin and D−R models are given in Table 3. The R2 value obtained from Langmuir model is close to 1.0 (R2 > 0.99), and this reveals that the Langmuir model represents best fit of experimental results than the other adsorption isotherm models, implying that sorption of all metal ions occur principally on homogeneous surface by monolayer adsorption process. The calculated RL values were found between 0.01 and 0.8 for all the metal ions indicating favorable adsorption. The RL values decrease with the increase of the initial concentration of metal ions, which reveal that the adsorption process is favorable at higher concentration of metal ions. The values of (N) in the Freundlich isotherm are less than unity in the range of 0.28−0.56, which reveals the favorable nature of adsorption process. The values of mean free energy E per molecule from the D-R isotherm model are 1291−3536 kJ mol−1 indicating that the adsorption process follows the chemisorption process. The positive values of apparent free energy E indicate that the adsorption process of metal ions is endothermic. 3.2.3. Effect of Shaking Time. In adsorption of metal ions, shaking time is the very important factor that directly affects the sorption kinetics. To examine the optimum time for achievement of equilibrium, batch studies were completed at 25 °C, optimum pH, and maximum metal ion concentration. Adsorption experiments were examined in the shaking time range of 5−30 min. The effect of shaking time on the amount of uptake of metal ions by MIDA is presented in Figure 8. The figure indicates that the adsorption capacity increases sharply with shaking time in the first 5 min. This is attributable to the existence of a large number of available sites. As time passes the adsorption rate was slow due to gathering of metal ions on the active sites until equilibrium is reached. Consequently, an additional increase in shaking time did not increase the removal of metal ions. The optimum shaking time within 25 min for Cu(II) and Pb(II) and 20 min for Zn(II) and Cd(II). This high adsorption rate shows that the adsorption of Cu(II), Pb(II), Zn(II), and Cd(II) occurs mostly on the surface of the MIDA chelating resin. 3.2.3.1. Batch Kinetic Studies. Kinetic parameters are vital for deciding the efficiency of the magnetic chelating resin and mechanism of the adsorption process. To examine the kinetic

Figure 8. Effect of shaking time on adsorption of Cu(II), Pb(II), Zn(II), and Cd(II) ions using MIDA.

equation representing the mechanism of metal ions adsorption onto MIDA, the experimental kinetic data was fitted to the pseudo-first-order model (eq 19)44 and pseudo-second-order model (eqs 20 and 21).45 ln(q − qt ) = ln −K1t

(19)

⎛1⎞ t 1 = + ⎜ ⎟t 2 qt K 2q ⎝q⎠

(20)

h = K 2q2

(21)

where q (mmol g−1) is the adsorption capacity at equilibrium, qt (mmol g−1) is the sorption capacity at time t (min), K1(min−1), and K2 (g mmol−1 min−1) are the rate constants of the firstorder and second order, respectively, h (mmolg−1min−1) is the initial adsorption rate constant, and the intercept C represents the thickness of the boundary layer. The kinetic parameters are given in Table 4. R2 values of the pseudo-second-order kinetic model, for all four metal ions, were closer to 1.0, and this indicates that the Table 4. First-Order, Second-Order, Elovich Equation and Intraparticle Diffusion Rate Constants model pseudo-firstorder kinetic equation pseudosecond-order kinetics

Elovich equation intraparticle diffusion equation

I

parameter −1

q (mmol g ) K1 (min−1) R2 q (mmol g−1) K2 (g mmol−1 min−1) h (mmol g−1 min−1) R2 α (mmol g−1 min−1) β (g mmol−1) R2 Kid (mmol g−1 min −1/2 ) C (mmol g−1) R2

Cu(II)

Pb(II)

Zn(II)

Cd(II)

2.93 0.161 0.985 4.54 0.354

3.4 0.134 0.953 3.9 0.27

2.94 0.17 0.990 2.7 0.11

1.37 0.126 0.991 2.52 0.1

7.29 0.999 7.33 1.32 0.992 0.388

4.1 0.997 2.15 1.07 0.998 0.415

0.801 0.999 2.06 1.85 0.996 0.29

0.655 0.997 1.86 2 0.992 0.272

2.18 0.882

1.53 0.898

1.02 0.959

0.915 0.965



Article

pseudo-second-order kinetic model could fit the adsorption data better than the pseudo-first-order model. Additionally, the theoretical value of adsorption capacity at equilibrium calculated from the pseudo-second-order model is much closer to the experimental data, and this reveals for a second time that the pseudo-second-order model is more appropriate to illustrate the adsorption of metal ions onto MIDA, and the chemisorption is possibly the dominant mechanism.13,36 It is also clear from Table 4 that the rate constant (K2) of Cu(II) is higher than the other metal ions representing a high attraction between Cu(II) and MIDA chelating resin. Consequently, the calculated initial adsorption rate constant (h) followed the order Cu(II) > Pb(II) > Zn(II) > Cd(II). This result once more indicates Cu(II) has the fastest initial adsorption rate between all metal ions, this is similar to other aminopoly(carboxylic acid) functionalized adsorbents.6,13,16,17 The Elovich equation is one of the most useful models for describing chemisorption on a highly heterogeneous adsorbent.46 A simplified linearized form of the Elovich equation is expressed using eq 22. qt =

1 1 ln(αβ) + ln t β β

Figure 9. Plot of Weber−Morris intraparticle diffusion model for sorption of Cu(II), Pb(II), Zn(II), and Cd(II) ions using MIDA.

(22)

where α (mmol g−1 min−1) is the initial sorption rate and β (g mmol−1) is the constant related to the degree of the surface coverage and activation energy for chemisorption. The values of each parameter are also given in Table 4. The R2 values for all metal ions close to 1 (>0.99) reveals again that the chemisorption is the dominant mechanism.13 The intraparticle diffusion kinetic model based on the equation developed by Weber and Morris is used to examine the diffusion mechanism of metal ions into the adsorbent.47 The intraparticle diffusion model is given by eq 23. qt = K idt 0.5 + C

(L) is the total volume of the solution, W (g) is the weight of MIDA. Thermodynamic parameters of adsorption process including Gibbs free energy changes (ΔGoads), enthalpy change (ΔHoads), and entropy change (ΔSoads) are obtained by eqs 25 and 26.48,49 o ΔGads = −RT ln Kd

ln Kd =

−0.5

where Kid (mmol g min ) is the rate constants of the intraparticle diffusion model and C is the intercept and represents the boundary layer thickness, that is, the larger the intercept, the greater the boundary layer effect. The WeberMorris interparticle diffusion plot of MIDA toward four metal ions is presented in Figure 9. It can be observed that each plot presents multilinearity, suggesting that two or more stages of adsorption take place. The first linear stage could be attributed to the external surface adsorption (surface or film diffusion) and be considered as a quick adsorption process. The second linear stage is attributed to the intraparticle diffusion as a slow adsorption process. The third stage reveals the final equilibrium step where intraparticle diffusion starts to reduce speed due to the extremely low metal ion concentrations in the solution. This reveals that adsorption kinetics of all metal ions may be limited concurrently by the intraparticle diffusion and film diffusion. 3.2.4. Adsorption Thermodynamic. To determine whether the adsorption process is spontaneous or not, the experiments were conducted at 25, 35, 45, and 55 K. The equilibrium constant Kd (L g−1) for uptake of metal ions is calculated using eq 24.48 Kd =

Co − Ce V Ce W

(25)

◦ ΔHads

− (26) R RT −1 −1 where R is the universal gas constant (8.314 J mol K ), T is the temperature (K) in Kelvin. The calculated parameters are tabulated in Table 5. ΔHoads and ΔSoads could be calculated from the slope and intercept of the straight line obtained from plotting ln Kd against 1/T, Figure 10, respectively. The results indicated that the values of Kd are in the order Cu(II) > Pb(II) > Zn(II) > Cd(II), which revealed that the affinity of Cu(II) onto MIDA chelating resin was higher than that of the other metal ions. The results also show that the values of ΔGoads for all metal ions at all temperatures are negative and decrease as temperature increases, which demonstrates the feasibility and spontaneous nature of the adsorption process and that the spontaneity increases as temperature increases. The positive values of ΔHoads suggested that an endothermic nature of the adsorption process. The positive values of ΔSoads imply an increase in randomness at the MIDA-solution interface during the sorption process attributable to the liberation of water molecules of chelation in the sorption of metal ions. ΔH < TΔSoads reveal that the adsorption of metal ions is an entropydriven process.18,36 3.3. Adsorption of Cu(II) Metal Ions Using Column Technique. 3.3.1. Effect of Bed Height. The breakthrough curves of Cu(II) adsorption onto MIDA at various bed heights with inlet metal ion concentration of 5 mmol L−1 and the flow rate of 1.0 mL min −1 are illustrated in Figure 11a. Three bed heights of 2.2, 4.4, and 6.6 cm, corresponding to 1, 2, and 3 g of MIDA chelating resin, respectively, were examined (Figure 11a). The results revealed that increasing bed heights from 2.2 to 4.4 to 6.6 cm resulted in an increase in both breakthrough time (tb) and the exhaust (or saturation) time (te) from 360 to

(23) −1

◦ ΔSads

(24)

−1

where Co (mmol L ) is the initial concentration of metal ions, Ce (mmol L−1) is the equilibrium concentration metal ions, V J



Article

Table 5. Thermodynamic Parameters for Uptake of Cu(II), Pb(II), Zn(II), and Cd(II) Kd (L g−1)

−ΔGoads (kJ mol−1)

ΔHoads (kJ mol−1)

metal ion

25 °C

35 °C

45 °C

55 °C

25 °C

35 °C

45 °C

55 °C

Cu(II) Pb(II) Zn(II) Cd(II)

5.67 4.26 1.86 1.56

6.69 4.88 2.03 1.70

8.09 5.66 2.23 1.86

10.11 6.69 2.45 1.97

4.25 3.55 1.52 1.11

4.91 4.08 1.82 1.37

5.58 4.61 2.12 1.62

6.25 5.14 2.42 1.87

ΔSoads (J mol−1 K−1) R2

15.62 12.18 7.48 6.35

66.67 52.8 30.19 25.04

0.9912 0.9945 0.9981 0.9965

6% and moreover the equilibrium (remaining) metal ion concentration (Ce) decreased by 0.27 mmol L−1 (Table 6). Conversely, it is expected that, the uptake (qe) of MIDA will remain reasonably constant for various bed length but in fact it was observed that the amount of metal ions adsorbed per gram of chelating resin (qe) inversely proportional to the bed height, demonstrating that bed with 2.2 cm showed the highest (qe) in comparison with 4.4 and 6.6 cm (Table 6). These results are in agreement with earlier published results.36 To keep a remarkable balance between adsorption capacity, treatment volume, chelating resin usage and economic efficiency of the removal process, 2.2 cm bed length was fixed for following experiments. 3.3.2. Effect of Flow Rate. The effect of the flow rate on the breakthrough curve was studied at different flow rates of (1.0, 2.0, 3.0 mL min−1) while maintaining Cu(II) concentration of 5 mmol L−1 and bed height of 2.2 cm (Figure 11b). The parameters for breakthrough curves are tabulated in Table 6. The results revealed that breakthrough time, exhaustion time decreased by increasing the flow rate from 1.0 to 3.0 mL min−1. Also, increasing the flow rate reduces the volume of effluent treated before the bed became saturated. On the other hand, at higher flow rate, less contact time followed by lower Cu(II)MIDA interaction and lower diffusion of metal ions onto the chelating resin, not all Cu(II) have sufficient time to transfer from solution through the pores in MIDA and thus the adsorption capacity (qe) decreased by 0.54 mmol g−1. Otherwise, the increase of the flow rate from 1.0 to 3.0 mL min−1 leads to decrease in the removal percentage (R%) by 8% and the remaining metal ions (Ce) increased by 0.42 mmol L−1

Figure 10. Arrhenius plots of ln Kd against (T−1) for uptake of Cu(II), Pb(II), Zn(II), and Cd(II) ions using MIDA.

460 to 680 min and 630 to 910 to 1250 min, respectively (Table 6). This was attributed to the more vacant metal binding sites and more chelating resin surface at higher bed depth, which meant that accordingly the total metal ions adsorbed onto MIDA increased. Comparable kinds of results have been obtained in previous researches.36,50 Furthermore, the increase in the bed height resulted in an increase in mass transfer zone, which made the slope of the breakthrough curves became flatter. At higher bed depth a larger volume of solution containing copper ions can be treated and a higher amount of metal ions can be adsorbed, so that when the bed length increased, the removal percentage (R%) of Cu(II) increased by

Figure 11. Break through curves for adsorption of Cu(II) using MIDA at different bed heights (a); different flow rates (b); different concentration (c). K



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Table 6. Ion Exchange Data for Adsorption of Cu(II) onto MIDA Using Fixed Bed Column at Different Bed Heights, Flow Rates and Concentrations tb (min)

process parameters

te (min)

△t (min)

−1

Zm (cm)

qe (mmol g−1)

Mad (mmol)

Mtot (mmol)

Ce (mmol L−1)

R (%)

2.19 1.63 1.56

2.19 3.27 4.68

3.15 4.55 6.25

1.52 1.41 1.25

69 72 75

2.19 1.92 1.65

2.19 1.92 1.65

3.15 3.05 2.7

1.52 1.85 1.94

69 63 61

2.19 2.45 2.75

2.19 2.45 2.75

3.15 3.6 4.35

1.52 3.19 5.5

69 68 63

−1

(F = 1.0 mL min , Co = 5 mmol L ) 360 630 270 0.94 460 910 450 2.18 680 1250 570 3.2 (Z = 2.2 cm, Co = 5 mmol L−1) 360 630 270 0.94 135 305 170 1.22 64 180 116 1.41 (Z = 2.2 cm, F = 1.0 mL min−1) 360 630 270 0.94 180 360 180 1.1 120 290 170 1.29

bed height (cm) 2.2 4.4 6.6 flow rate (mL min−1) 1.0 2.0 3.0 concentration (mmol L−1) 5 10 15

Table 7. Kinetics Model Parameters and Comparison between Thomas and Yoon−Nelson Models column conditions Z (cm) F (mL min−1) 2.2 4.4 6.6 2.2 2.2 2.2 2.2

1 1 1 2.0 3.0 1 1

Thomas model

Yoon−Nelson model

Co (mmol L−1)

KTh × 10−3 (L mmol−1 min−1)

qTh (mmol g−1)

R2

KYN × 10−3 (min−1)

τ(cal) (min)

τ(exp) (min)

R2

5 5 5 5 5 10 15

4.82 2.36 1.98 6.36 7.86 2.43 2.26

2.43 1.72 1.66 2.02 1.76 3.07 3.2

0.981 0.994 0.992 0.986 0.984 0.985 0.981

24.1 11.8 9.9 31 39.2 24.3 38.5

485 691 996 201 118 277 203

481 690 997 200 119 275 198

0.981 0.994 0.992 0.986 0.984 0.985 0.981

to apply the experimental data for investigating the metal ions interaction behavior and to estimate the breakthrough curves. Thomas Model. Thomas’s kinetic model, derived from a Langmuir sorption isotherm and a second order sorption kinetics, is appropriate for a sorption process where external and internal diffusion limitations are not present. Thomas’s kinetic model was used to expect the dynamic behavior of metal ion adsorption. The linearized form of Thomas model is expressed by eq 27.52

(Table 6) because metal ions left the column before saturation is reached. Alternatively, small difference between Zm values under various flow rates which could be due to the same reason for both the breakthrough time (tb) and exhaustion time (te) decreased with increasing flow rate.36,50 Accordingly, the flow rate of 1.0 mL min−1 with the highest qe will be used in the next studies. 3.3.3. Effect of Initial Concentration. The effect of Cu(II) concentration on the adsorption process was studied using different concentrations of 5, 10, and 15 mmol L−1 at a constant flow rate of 1.0 mL min−1 and bed height of 2.2 cm. The results are given in Figure 11c and Table 6. As indicated in Figure 11c the shape of the breakthrough curves changed drastically with an increase in Cu(II) concentration. The higher initial metal concentration resulted in the faster saturation and the sharper breakthrough curves shifted to the left. This earlier exhaustion may be due to greater concentration gradient and smaller resistance of mass transfer at a higher Cu(II) concentration. The breakthrough time and exhaustion time decreased by increasing Cu(II) concentration from 5 to 15 mmol L−1 with a small increase in mass transfer zone (Zm). An increase in Cu(II) concentration from 5 to 15 mmol L−1 gave an earlier saturation time from 630 to 290. Also, a lower adsorption capacity (qe) and lower removal percentage (R%) was obtained by increasing Cu(II) concentration from 5 to 15 mmol L−1, which could be due to the higher driving force for diffusion and improved metal ions loading rate with increased in initial Cu(II) concentration. Similar results have been published previously.51,52 As a result of the adsorption capacity (qe), 5 mmol L−1 initial metal concentration was selected for subsequent studies. 3.3.4. Kinetic Modeling of Breakthrough Curves. Two theoretical models in column sorption technique namely Thomas model and Yoon Nelson model52,53 were examined

⎛C ⎞ KThqThW K C ln⎜ o − 1⎟ = − Th o Veff F F ⎝ Ceff ⎠

(27)

where KTh (L mmol−1min−1) is the Thomas rate constant. Constants of the Thomas model at different column adsorption parameters were listed in Table 7. From Table 7, it was observed that this model fit well with the present experimental results (R2 ≥ 0.981). When the bed length was increased the (qe) and (KTh) values decreased, which may be attributed to increase in mass transfer resistance with increasing bed length in columns. With increasing flow rate, the value of KTh increased and qTh decreased, which might be due to the lesser contact time resulting in insufficient contact between metal ion with the accessible active sites on the surface of the chelating resin. By increasing influent concentration, the qe value increased and KTh value decreased due to larger driving force of concentration gradient generated between metal ions on MIDA chelating resin and metal ions in the solution. Furthermore, qTh obtained from the Thomas model were close to the column adsorption capacity (qe) calculated in all experimental conditions. The obtained results are in agreement with the previous observations.36 Yoon−Nelson Model. Yoon−Nelson model is a quite simpler model than Thomas model because it does not need L



Article

full data about the type of adsorbate.53 The Yoon−Nelson model suggests that the rate of reduction in the possibility of sorption for each adsorbate is directly proportional to the possibility of adsorbate sorption and the probability of adsorbate breakthrough on the resin. The linear equation of the model is expressed by eq 28. ln

Ceff = KYNt − τKYN Co − Ceff

4. CONCLUSIONS A new magnetic chelating resin (MIDA) was synthesized successfully based on the modification of magnetic polyvinylamine resin with IDA. MIDA showed strong affinity toward Cu(II), Pb(II), Zn(II) and Cd(III) and the adsorption capacity is greatly dependent on pH of solution, concentration of metal ions, shaking time and temperature of solution. The adsorption of metal ions using MIDA could be well described by the pseudo-second-order kinetic model, and the adsorption is a Langmuir monolayer chemical adsorption. The obtained thermodynamic parameters reveal that the adsorption of metal ions is an endothermic and spontaneous process derived by entropy. The column adsorption study was performed for the removal of Cu(II), and the results reveal that the adsorption of Cu(II) using MIDA is dependent on bed height, flow rate, and influent concentration. The column adsorption experimental data were fitted well with Thomas and Yoon−Nelson models. Regeneration experiments showed the good potential of the MIDA chelating resin for reuse, although a small decrease in adsorption capacity was found in subsequent cycles.

(28)

−1

where KYN (min ) is the Yoon−Nelson rate constant, τ (min) is the time required for 50% exchange breakthrough and t (min) is the breakthrough time. The values of KYN and τ were estimated from the slopes and intercepts of the linear plots at different bed lengths, flow rates, and influent concentration, and the results are given in Table 7. The τ value increased and the rate constant (KYN) value decreased with increasing bed height. The τ value decreased and KYN value increased with increasing the flow rate and influent concentration due to the fast saturation of MIDA in the column. Furthermore, the data indicate that the values of (τcal) which was estimated from the Yoon−Nelson plot were approximately comparable to the experimental values (τexp), which reveals that the experimental results fitted well with Yoon−Nelson model. The linearized equations of the above models reveal that both kinetic models give the same R2 values resulting in both the Thomas and Yoon−Nelson models could be used to illustrate the behavior of metal ions adsorption. With respect to the Thomas model, it analyzes the effect of sorption capacity; on the other hand, the Yoon−Nelson model accurately predicts the time required for 50% breakthrough. These parameters help to better explain the effectiveness of each individual model. 3.3.5. Column Regeneration. For using the chelating resin for the maximum efficiency, for repeated use of chelating resin and for minimizing the operation cost, the regeneration and reuse of the chelating resin in the treatment plant is necessary. The most favorable eluting agent should be efficient, nonpolluting, nondamaging to MIDA chelating resin and cheap. In this study, 0.1 M HNO3 solution can successfully desorb Cu(II) ion from loaded MIDA with higher desorption efficiency. In the present work, MIDA was reused for six successive adsorption− desorption cycles at 2.2 cm bed height, flow rate of 1.0 mL min−1 and 5 mmol L−1 of Cu(II). After each column regeneration by 0.1 M HNO3, the regenerated resin was washed with deionized water followed by neutralization by 0.1 M NaOH to obtain the salt form (−COONa) which was reused in consecutive adsorption experiments. Figure 12 shows

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected], [email protected]. Tel: +966531559921, +201005031728. ORCID

Salah M. El-Bahy: 0000-0002-1652-3522 Funding

This study was funded by the Academic Research Center at Taif University, Project No. 1-438-5609. Notes

The author declares no competing financial interest.

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REFERENCES

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Figure 12. Adsorption−desorption cycles of MIDA.

the adsorption−desorption cycles. The adsorption capacity was observed to decrease slightly from 100% to 86% after six adsorptions−desorption cycles. Generally, MIDA is a competent adsorbent for adsorption of metal ions from aqueous solution. M



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