Fast removal of Cu(II) and Hg(II) from aqueous solutions using

Desalination and Water Treatment

30 (2011) 254–265 June

www.deswater.com 1944-3994/1944-3986 # 2011 Desalination Publications. All rights reserved doi: 10.5004/dwt.2011.2082

Fast removal of Cu(II) and Hg(II) from aqueous solutions using kaolinite containing glycidyl methacrylate resin Ahmed M. Doniaa , Asem A. Atiab, Rama T. Rashadb a

Department of Chemistry, Faculty of Science, Menoufia University, Egypt Tel.: þ20176130046; Fax: þ238356313; email: [email protected], [email protected] b Soil, Water and Environment Research Institute, Agricultural Research Center: Giza, Egypt Received 8 June 2010; accepted 9 January 2011

ABSTRACT

A clay-polymer chelating resin was prepared through copolymerization of glycidyl methacrylate (GMA) with N,N’–methylene bis-acrylamide (MBA) as a cross-linker in the presence of 5% kaolinite mineral. The resin obtained was chemically modified through the reaction with tetraethylenepentamine (TEP). A comparison study was held between the modified clay-containing resin and a clay-free one. The prepared resins were characterized by FT-IR, XRF, TGA, BET–surface area and SEM techniques. The adsorption behavior of both resins towards Cu (II) and Hg (II) at different conditions was studied. Kinetics, isotherms and thermodynamic parameters of the adsorption process were also investigated. The clay-containing resin exhibited a higher thermal stability, greater surface area and higher uptake values than the clay-free one. Uptake values up to 2.38 mmol/g (479.57 mg/g) for Hg (II) and 1.95 mmol/g (124.02 mg/g) for Cu (II) were reported on the clay-containing resin. The adsorption process of both metal ions followed Langmuir and Freundlich isotherms and is dominated by enthalpic rather than entropic changes. The regeneration of the loaded resin was carried out using KI and HCl for elution of Hg (II) and Cu (II), respectively. Keywords: Adsorption: Kaolinite; Glycidyl methacrylate resin; Removal; Metal ions

1. Introduction Heavy metal ions represent a serious environmental problem because they contaminate both the soil and water resources. Heavy metals convert into highly toxic forms by some aquatic living organisms causing different renal and nervous system problems [1–6]. Several methods have been developed for the removal of the heavy metals from wastewater, e.g., liquid– liquid extraction (LLE), electro-deposition, coagulation, ion-exchange, membrane filtration, flotation,

Corresponding author

precipitation, electrochemical separation and reverse osmosis. But most of them suffer from economical and technical problems, such as excessive time requirements, high costs and production of highly toxic sludge. The solid-phase extraction (SPE) has gained a rapid progress in the field of pollution removal [7–9]. Chelating resins are increasingly used as efficient adsorbents for various metal ions. They display a high adsorption capacity, greater selectivity and durability compared with the conventional types of ionexchangers [7,10–13]. Divinylbenzene (DVB) resins loaded by different functionalities like iminodiacetate, amines, ethylenediamine (en), tetraethylenepentamine

A.M. Donia et al. / Desalination and Water Treatment 30 (2011) 254–265

(TEP), thiourea, hydroxamic acid, amidoxime, thiol and thiazole, were used as chelating resins towards different metal ions. Modified glycidyl methacrylate (GMA) resins with different hydrophilic/hydrophobic cross-linkers, different functionalities, and different embedded metal oxide were prepared and investigated towards the removal of various metal ions from aqueous solution [10,11,14–20]. Clay-containing polymers are very attractive due to the fact that a small amount of clay can lead to a great improvement in the properties of the polymer. Such as, thermal stability, corrosion resistance, ionic conductivities, surface area, fire and mechanical properties of the polymer [21–26]. Removal of copper and mercury from aqueous medium using chelating resins as adsorbents was in the scope of many studies [27–29]. Amine chelating resins have shown adsorption capacities of 25.6 and 103.16 mg/g for copper and 344.8 mg/g for mercury. Batch and column experiments are widely used for assigning the adsorption behavior and calculating the adsorption parameters of metal ions by chelating resins [30]. In the present study, a kaolinite clay-containing glycidyl methacrylate resin will be prepared and loaded with tetraethylenepentamine (TEP) functionality. The adsorption behavior of the resin obtained towards Cu (II) and Hg (II) ions will be investigated using batch and column methods at different experimental conditions. The kinetic and thermodynamic characteristics of the adsorption reaction will also be studied.

2. Experimental 2.1. Materials Glycidyl methacrylate (GMA), N,N’-methylene bis-acrylamide (MBA), benzoyl peroxide (Bz2O2) were Aldrich products. Bz2O2 was purified through crystallization from ethanol/methanol mixture. Tetraethylenepentamine (TEP) was Fluka product. Kaolinite mineral (*Al2Si2O5(OH)4) and CuSO45H2O were Merck. HgCl2 was P.G.VI product (VEB BERLIN.CHEMIE). All other chemicals were Prolabo products and were used as received. 2.2. Preparation of the resins 2.2.1. Preparation of kaolinite-containing GMA/MBA resin The resin was prepared through the polymerization of GMA in the presence of MBA as a cross-linking agent at a weight ratio 9.5:0.5. A 0.5 g kaolinite and a 0.1 g Bz2O2 (initiator) were added to the mixture of GMA/MBA with stirring. One milliliter isopropyl

255

alcohol and 12.6 mL cyclohexane were mixed and then added to the former solution. All the contents were poured into a flask containing 73 mL (1%) polyvinyl alcohol and heated on a water bath at 75–80 C with continuous stirring for 3 h. A brittle white precipitate was formed, filtered off then washed repeatedly with methanol to remove the unreacted materials and dried in air. The resin obtained was referred as R1. The kaolinite free resin (R2) was obtained following the same method, except the use of kaolinite. 2.2.2. Immobilization of R1 and R2 by tetraethylenepentamine (TEP) The resins (R1 and R2) were loaded by TEP as follows: One gram of the resin was added to 4 g TEP dissolved in 12 mL DMF. The reaction mixture was heated at 75–80 C for 72 h in an oil bath. The products obtained were filtered off, washed with methanol and dried in air. The resins obtained were referred as R1A and R2A, respectively.

2.3. Characterization and estimation of amino groups’ concentration of the resins IR spectra of both resins were performed using FT-IR Nexeus-Nicolite-Model 640-MSA. X-ray fluorescent (XRF) measurements were carried out using Philips X-ray generator model PW 3710/31 with Cu Ka radiation. Thermo-gravimetric analysis (TGA) was performed using Shimadzu TGA 50H instrument. Experiments were performed with 2–3 mg of the sample under N2 atmosphere at a flow rate of 30 mL/min and a heating rate of 10 C/min. Surface area and total ˚ diameter pore volume for the pores smaller than 25.6 A were measured by N2 adsorption isotherm using Quanta chrome NOVA Automated Gas Sorption System and by Brunauer-Emmett-Teller (BET) method. The surface morphology of the resin was examined using JEOL, JEM-100S (Japan) model scanning electron microscopy. The stability of both resins in aqueous medium at high temperature (up to 70 C) and at low temperature (room temperature 28 C) was tested. In addition, the stability over a pH range (2–10) and in organic solvents (methanol and benzene) was also tested. A 0.5 g of R1A or R2A was immersed in a 50 mL of the selected medium for 24 h. Then; the resin was filtered, washed out thoroughly by distilled water, dried at 40 C and weighed. No loss of resin weight was recorded for all tested medium types. The concentration of amino groups on R1A and R2A was estimated using a volumetric method [16]. Fifty milliliters of HCl (0.05 M) was added to 0.5 g resin and conditioned for 24 h on a shaker. The residual


256

concentration of HCl was measured through titration against 0.05 M NaOH and phenolphthaline as an indicator. The number of moles of HCl interacted with the amino groups and consequently the amino groups’ concentration was calculated.

concentration and natural pH. The flasks were conditioned at 300 rpm while keeping the temperature at 28, 40 or 50 C for 1 h. Later on, the residual concentration was determined and the metal ion uptake was estimated. 2.4.3. Effect of pH

2.4. Adsorption of metal ions by the resins using batch method A stock solution (5 103 M) of Cu (II) or Hg (II) was prepared in distilled water. A stock solution of EDTA di-sodium salt (5 103 M) was also prepared and standardized against MgSO47H2O using Eriochrome Black-T (EBT) as an indicator [16]. The pH of titration was adjusted using ammonia/ammonium chloride (pH 9–10) and acetic acid/sodium acetate (pH 3.8–5.8) buffers. The concentration of metal ion was determined via titration against 5 103 M EDTA using Mureoxide and PAR as indicators for Cu (II) and Hg (II), respectively [15,16]. Each data point was taken as the average of three measurements with standard deviation of 1% +0.5. The adsorption study using batch method was performed as follows: For each experiment, a set of flasks was used. A 0.1 g of R1A or R2A resin was placed in each flask containing 100 mL Cu (II) or Hg (II) solution at initial concentration of 5 103 M and natural pH [5.5 for Cu (II) and 5 for Hg (II)]. The contents of the flask were equilibrated on a Vibromatic-384 shaker at 300 rpm and at 28 C. Five milliliters of the solution were taken at the end of the experiment and then filtered off. The residual concentration of metal ion was determined and the uptake (mmol/g) was calculated according to the equation [31] ðC Ce Þ qe ¼ V; m

Uptake experiments at different pH values were carried out. The pH of the contents of the flask was adjusted using HCl, NaOH and NH4OH. Five milliliters of the solution were taken and then filtered off. The residual concentration of metal ion was determined and the uptake (mmol/g) was calculated. 2.5. Column method 2.5.1. Effect of flow rate A 0.1 g resin was packed in a plastic column of 3 cm length and 1 cm diameter to obtain 0.3 cm bed height. A small amount of glass wool was placed at the bottom of the column to keep the contents. Solution of Cu (II) or Hg (II) at an initial concentration (Co) of 5 103 M was allowed to flow downward under the force of gravity at flow rates of 0.2, 0.5 or 1 mL/min. Five milliliters of the underflow solution were removed at constant time intervals where the residual concentration of metal ion was determined through titration against EDTA. The process was continued until the outlet concentration matches the initial concentration of the metal ion. The outlet metal ion concentration was plotted against the flow time to determine the breakthrough for different flow rates. 2.5.2. Effect of bed height

ð1Þ

where Co and Ce is the initial and equilibrium concentration of metal ion (mmol/L), respectively, V is the volume of solution (mL) and m is the mass of the resin (g). 2.4.1. Effect of time Metal ion uptake as a function of time was carried out by taking 5 ml of the solution at different time intervals and then filtering them off. The residual concentration of metal ion was determined and the uptake (mmol/g) was calculated according to Eq. (1).

The effect of bed height was studied at a flow rate of 1 mL/min. A 0.05, 0.1 or 0.2 g resin was packed in a plastic column of 3 cm length and 1 cm diameter to obtain bed heights of 0.15, 0.3 or 0.6 cm, respectively. Solution of Cu (II) or Hg (II) at an initial concentration of 5 103 M was allowed to flow downward the column under the force of gravity. Five milliliters of the underflow solution were removed at constant time intervals where the residual concentration of metal ion was determined through titration against EDTA. The process was continued until the initial concentration of the metal ion matches the outlet one. The outlet metal ion concentration was plotted against flow time to give the breakthrough for different bed heights.

2.4.2. Adsorption isotherms Complete adsorption isotherms were obtained using a series of flasks. Each flask contains 0.1 g resin and 100 mL of metal ion solution at the desired initial

2.6. Elution experiments The column was packed by 0.1 g of resin then loaded with Cu (II) or Hg (II) at a flow rate of 1 mL/


min. The loaded resin was washed thoroughly by distilled water and then subjected to elution using 1 M HCl for Cu (II) and 0.5 M KI for Hg (II). The concentration of the released metal ion in the down-flow was determined. The process of loading/elution was repeated for three times. The efficiency of the elution was calculated according to the following equation [18] Efficiency of elution ð%Þ Total uptake in the second run ¼ 100: Total uptake in the first run

(R1A) is characterized by a higher uptake capacity as well as faster kinetics than that of the clay free one (R2A). Maximum uptake capacity was achieved within the initial 10 min for R1A but more than 60 min for R2A. This may be attributed to the formation of stretched film of the resin over the clay particles which characterized by a larger surface area as well as a higher concentration of exposed active sites. The concentration of amino groups was 3.5 and 1.8 mmol/g for R1A and R2A, respectively. The data presented in Fig. 3 were treated according to the pseudo-first (Eq. (2)) and pseudo-second (Eq. (3)) order kinetics [34]

3. Results and discussion 3.1. Characterization of resins FT-IR spectra of R1A and R2A are shown in Fig. 1. Characteristic bands for kaolinite at 3694.94, 1008.59, 937.24, 647.97, 540.94, 472.74 and 423.3 cm1 appear with low intensity in the spectrum of R1A [32]. These peaks are completely absent in the spectrum of R2A. The observed sharp and intense peak at 1661.37 cm1 may be related to the H-bonded C¼O group of the resin with the silanol SiOH group of the clay (C¼O. . ..H. . ..OSi) [33]. On the other hand, the XRF spectrum of R1A confirms the presence of clay through the appearance of peaks related to the –Si– and –Al– moieties at 2y ¼ 109 and 145 , respectively. Such peaks were completely absent in the XRF spectrum of R2A. Thermal analysis of R1A and R2A is shown in Fig. 2. R1A resin was thermally stable up to 330.91 C. The first weight loss point was observed at 330.91 C followed by another at 389.48 C. For R2A resin, four weight loss points were observed at 52.04, 192.27, 410.54 and 709.71 C. The results of BET analysis for both R1A and R2A resins are listed in Table 1. An increased surface ˚ diameter area and total pore volume for pores < 25.6 A was observed for R1A resin compared with that of R2A one. It may be an indication of the enhanced arrangement of functional groups of the polymer around the encapsulated clay particles. This has lead to more exposed active sites available for adsorption in R1A. Both resins were found to be stable in aqueous medium over a temperature range 28–70 C, stable in acidic and basic medium over a pH range of 2–10 and in methanol and benzene as examples of organic solvents. 3.2. Batch method 3.2.1. Kinetics studies Fig. 3 shows the uptake of both Cu (II) and Hg (II) by resins R1A and R2A as a function of time at 28 C and natural pH (pH 5.3). The clay-containing resin

257

log ðqe qt Þ ¼ log qe

t ¼ qt

1 k2 q2e

k1 t 2:303

t þ ; qe

ð2Þ

ð3Þ

where qe and qt refer to the amount (mmol/g) of metal ion adsorbed at equilibrium and at time t (min), respectively; k1 and k2 (g/mmol min) are the overall rate constant of pseudo-first and pseudo-second order reaction, respectively. The values of k1, k2 and qe were obtained from the straight line plots of log (qe – qt) or (t/qt) vs t (min) and reported in Tables 2 and 3. As shown in Table 2, the qe values of pseudo-second order model are more comparable to the experimental ones. This indicates the validity of this model to describe the adsorption kinetics and the effect of the textural properties of both R1A and R2A on the adsorption process.

3.2.2. Adsorption isotherms Fig. 4 shows the uptake of both Cu (II) and Hg (II) on R1A and R2A at the natural pH and 28 C. For both metal ions, the uptake increases as the initial concentration increases tell reaches a plateau. At the plateau region, the maximum uptake values of R1A are 1.95 and 2.38 mmol/g for Cu(II) and Hg(II), respectively. Whilst R2A displays a relatively lower uptake values of 1.07 and 1.3 mmol/g for Cu(II) and for Hg(II), respectively. According to Giles classification system, the isotherms obtained can be classified as L2-type with a monolayer adsorption. The uptake data were treated according to the Freundlich (Eq. (4)) and Langmuir (Eq. (5)) isotherms [15,35–37] log qe ¼ 1=b log Ce þ log a

ð4Þ


258

Fig. 1. FT-IR spectra for R1A and R2A.

Ce ¼ qe

Ce 1 þ KL Qmax Qmax

ð5Þ

where qe is the amount adsorbed of metal ions at equilibrium concentration (mmol/g), Ce is the equilibrium concentration of metal ions in solution

(mmol/L), a (L/g) and b are parameters related to the favor – ability and adsorption capacity. These parameters were obtained from the intercept and slope of the straight line plotted between log qe against log Ce and reported in Table 4. The data indicates that the adsorption process is not restricted to one specific class of sites and assumes surface heterogeneity.


259

Fig. 2. Thermo-gravimetric analysis (TGA) of R1A and R2A.

Values of b > 1 represent favorable adsorption conditions [37]. KL is the Langmuir binding constant which is related to the strength of adsorbent/adsorbate interaction (L/mmol). Plotting of Ce/qe against Ce gives a straight line with a slope and an intercept equal to 1/ Qmax and 1/KLQmax, respectively. The values obtained of Qmax and KL is given in Table 5. Generally, the KL values of R2A are lower than those of R1A which indicates a better binding of adsorbed metal ions by R1A than R2A. Fig. 5 shows the effect of temperature on the uptake of Cu (II) or Hg (II) by R1A. For Cu (II), the uptake decreases as the temperature increases. But for Hg(II),

the uptake increases as the temperature increases. The different behavior of adsorption/temperature process may be attributed to the different nature of interaction and/or the type of complex formed between metal ion and active sites [35]. Table 1 The results of BET analysis for both R1A and R2A resins Resin

Surface area (m2/g)

Total pore volume (cm2/g), ˚ diameter pores < 25.6 A

R1A R2A

117.88 59.37

0.02910 0.01487


260 2.8

Cu(II)

constant called separation factor (RL) which is defined by the following relationship [38,39]

R1A R2A

2.4

RL ¼

Uptake, mmol/g

2.0

1.2 0.8 0.4

0

50

100

150 200 Time, min

250

300

350

lnKL ¼

3.2

Hg(II)

H S þ : RT R

ð7Þ

2.0

The values of H and S were calculated from the slope and intercept of the straight line of plotting ln KL versus 1/T and reported in Table 7. The Gibbs free energy of adsorption (G ) was also calculated from the relation [35]

1.6

G ¼ H TS

1.2

The observed decrease in the negative values of G with increasing temperature (Table 7) implies that the sorption becomes less favorable at higher temperatures. The negative value of H indicates an exothermic nature for the adsorption process. It is also seen that, at all temperatures |H | > |TS |. This indicates that the adsorption process is dominated by enthalpic rather than entropic changes [35].

2.8

R1A R2A

2.4 Uptake, mmol/g

ð6Þ

The RL value indicates whether the adsorption is irreversible (RL ¼ 0), favorable (0 < RL < 1) or unfavorable (RL ¼ 1). The values of RL (Tables 5 and 6) were found to lie between zero and one. This implies that the adsorption of both Cu (II) and Hg (II) on R1A from aqueous solution is favorable under the conditions used in this study [38]. The thermodynamic parameters of adsorption process were calculated from the following Van’t Hoff relation [35]

1.6

0.0

1 : 1 þ KL C

0.8 0.4 0.0

0

50

100

150 200 Time, min

250

300

350

Fig. 3. Effect of contact time on the uptake of Cu(II) and Hg(II) by R1A and R2A at 28 C and natural pH.

The adsorption data of isotherms at different temperatures were treated according to Langmuir adsorption model (Eq. (5)). The data obtained for Qmax and binding constants KL are reported in Table 6. The essential features of Langmuir adsorption isotherm can be expressed in terms of a dimensionless

ð8Þ

3.2.3. Effect of pH Fig. 6 shows the uptake of both Cu (II) and Hg (II) by R1A as a function of pH. At natural pH, the uptake could be attributed to the formation of resin–metal ion complex as follows [15] RNH2 þ M2þ $ RNH2 ! M2þ

ð9Þ

Table 2 Kinetic parameters for the adsorption of Hg(II) by R1A and R2A Pseudo-first order model Resin

qeexp (mmol g1)

qecal (mmol g1)

k1 (min )

R1A R2A

2.38 1.295

1.126 0.985

0.253 0.012

1

Pseudo-second order model

R

qecal (mmol g1)

h (mmol g1 min1)

k2 (g mmol1 min1)

R2

0.9770 0.9983

2.39 1.295

3.78 0.049

0.661 0.0293

0.9999 0.9875

2


261

Table 3 Kinetic parameters for the adsorption of Cu(II) by R1A and R2A Pseudo-first order model

Pseudo-second order model

Resin

qeexp (mmol g1)

qecal (mmol g1)

k1 (min1)

R2

qecal (mmol g1)

h (mmol g1 min1)

k2 (g mmol1 min1)

R2

R1A R2A

1.95 1.07

0.706 0.91

0.188 0.0348

0.8995 0.9977

1.97 1.14

3.84 0.0769

0.989 0.0592

0.9999 0.9997

where M2þ is the metal cation (Hg2þ or Cu2þ). The observed decrease in the uptake of Cu (II) as the pH decreases may be attributed to the partial protonation of the amino groups, which hinders the resin/metal 3.0 Cu(II)

Uptake, mmol/g

2.5

2.0

1.5

1.0

þ RNHþ 3 Cl þ HgCl3 ! RNH3 HgCl3 þ Cl

R1A R2A

0.5

0.0

ion interaction. At pH < 2 no appreciable uptake on resin was detected. This may be due to the complete blocking of active sites by protonation. The observed lower uptake at pH 10, may be attributed to the partial desorption of Cu (II) from the resin in the form of soluble Cu (II)–amine complex [16]. For Hg (II), high uptake value was recorded at the pH 5 (natural). It may be attributed to the presence of free lone pair of electrons on nitrogen suitable for coordination with the metal ion to give the corresponding resin–metal complex. The higher uptake value observed at pH ¼ 3 may be attributed to the complex formation along with the exchange between formed HgCl3– (in excess of Cl–) anion and protonated –NH3þ groups [35] which may be represented as follows:

0

2

4 6 8 Equilibrium concentration, mM

10

3.0

ð10Þ

It is seen that R1A resin is generally more selective for the removal of Hg2þ than Cu2þ especially in strong acidic medium. For example, the mixture of both metal ions gives uptake values 2.1 and 1.3 mmol/g for Hg (II) and Cu (II), respectively, at pH 5.3. Whilst at pH 3, the uptake values were 2.4 and 1.1 mmol/g for Hg (II) and Cu (II), respectively.

Hg(II)

Uptake, mmol/g

2.5

3.3. Column method 3.3.1. Effect of flow rate

2.0

The breakthrough curves of the R1A resin towards Cu (II) and Hg (II) at flow rates of (0.2, 0.5 and 1.0 mL/min) and a fixed bed height of 0.3 cm are shown in Fig. 7. It is noticed that the breakthrough

1.5

1.0 R1A R2A

0.5

0.0

Table 4 Freundlich parameters for the adsorption of Cu(II) and Hg(II) by R1A and R2A Cu(II)

0

2

4 6 8 Equilibrium concentration, mM

10

Fig. 4. Adsorption isotherms for Cu(II) and Hg(II) adsorption on R1A and R2A at 28 C and natural pH.

Hg(II)

Resin

a (L/g)

b

R2

a (L/g)

b

R2

R1A R2A

24.02 3.66

1.61 1.53

0.9784 1.0000

20.97 28.61

1.37 2.11

0.9502 0.9919


262

Table 5 Langmuir parameters for the adsorption of Cu(II) and Hg(II) by R1A and R2A Cu(II)

Hg(II)

Resin

qeexp (mmol g1)

Qmax (mmol g1)

KL (L mmol1)

RL

R2

qeexp (mmol g1)

Qmax (mmol g1)

KL (L mmol1)

RL

R2

R1A R2A

1.95 1.07

1.95 0.97

7.76 0.598

0.026 0.997

0.9828 1.0000

2.38 1.295

2.49 1.495

5.25 1.76

0.019 0.994

0.9892 0.9350

obtained are shown in Fig. 8. The influence of bed height was tested in terms of breakthrough time (tb) and saturation time (ts). The uptake value of Hg (II) on the resin was found to be directly proportional with bed height. Bed depth service time model (BDST) is a simple model, which states that bed height (Z) and saturation time (ts) of the column gives a linear relationship, as given in the following equation [35] N Z 1 C ts ¼ ln 1 ð11Þ C Ka C Ct

4

Uptake, mmol/g

Cu(II) Hg(II)

3

2

1

20

30

40 50 Temperature, °C

60

70

Fig. 5. Effect of temperature on the uptake of Cu(II) and Hg(II) on R1A at 28 C and at natural pH.

points occur faster at higher flow rates. This behavior may be attributed to the insufficient residence time, which negatively affects the interaction as well as the diffusion of metal ions through the pores of the resin. 3.3.2. Effect of bed height The effect of bed height on the metal ion uptake was studied at 0.15, 0.3 and 0.6 cm bed heights while the flow rate was held constant at 1 mL/min. The data

where Ct is the concentration of the metal ion (mmol/ L) at the saturation time just prior the initial concentration, Co (i.e. Co/Ct ¼ 100/99), No is the total adsorption capacity (mmol of solute/L of sorbent bed), is the linear velocity (cm/min) and Ka is the rate constant of adsorption (L/mmol min). Fig. 9 shows the plot of Z against ts. The values of No and Ka were calculated from the slope and intercept of the BDST plots, respectively. If Ka is large, even a short resin bed will avoid the breakthrough limit. In the case of small values of Ka a progressively longer bed would be required to extend the breakthrough point. The values of Ka for sorption of Cu (II) and Hg (II) by the investigated resin are 0.665 and 0.074 L/mmolmin, respectively. The critical bed height (Z0) can be calculated by setting ts ¼ 0 in Eq. (10) and rearranging to get [35] C Z ¼ ln 1 ð12Þ Ka N Cb

Table 6 Langmuir parameters at different temperatures for the adsorption of Cu(II) and Hg(II) by R1A Cu(II)

Hg(II)

Temp., ( K)

qeexp

KL (mmol g1) Qmax(mmol g1) (L mmol1) RL

R2

301 313 323 333

1.95 1.59 1.11 1.47

0.9828 0.9919 0.9987 0.9889

1.95 1.73 1.24 1.68

7.76 4.20 4.52 2.29

0.026 0.045 0.045 0.080

qeexp

KL (mmol g1) Qmax(mmol g1) (L mmol1) RL

R2

2.38 2.66 2.97 2.98

0.9892 0.9985 0.9796 0.9681

2.49 2.93 3.01 3.099

5.25 3.74 2.46 1.67

0.019 0.045 0.039 0.059


263

Table 7 Thermodynamic parameters for the adsorption of Cu(II) and Hg(II) by R1A Cu(II)

Hg(II)

Temp., ( K)

Go (kJ mol1)

TSo (kJ mol1)

Ho (kJ mol1)

So (J mol1 K1)

Go (kJ mol1)

TSo (kJ mol1)

Ho (kJ mol1)

So (kJ mol1)

301 313 323 333

4.99 4.10 3.57 2.40

15.95 16.85 17.38 18.55

20.95

52.69

4.30 3.29 2.43 1.58

25.68 26.69 27.55 28.40

29.98

85.31

where Cb is the breakthrough metal ions concentration (mmol/L). The critical bed heights of the resin towards Cu (II) and Hg (II) are found to be 1.7 and 17.32 cm, respectively.

GMA/MBA resin with TEP. The uptake of Cu (II) and Hg (II) by the resin obtained was investigated and compared with a clay-free resin using the batch and 1.0

3.4. Resin regeneration

Cu (II) 0.8

0.6 Ct/Co

For the repeated use, elution of Cu (II) and Hg (II) from the resin packed in the column was carried out at a flow rate of 1 mL/min using 1 M HCl or 0.5 M KI, respectively. Loading and elution of the studied metal ions on the resin was repeated for three cycles. Elution of Hg (II) using HCl was avoided due to the possibility of formation of HgCl3– which interacts with the resin via ion-exchange mechanism. Up to 90–93% elution efficiency was achieved for Cu (II) and Hg (II) from the resin R1A.

0.4

0.2 mL/min 0.5 mL/min 1.0 mL/min

0.2

4. Conclusion

0.0

A kaolinite clay-embedded chelating resin was prepared by subsequent treatment of kaolinite containing

0

50

100

150 200 Flow time, min

250

300

1.0

3.5

Hg (II)

Cu(II)

3.0

0.8

Hg(II) 0.6 Ct/Co

Uptake, mmol/g

2.5 2.0

0.4

1.5

0.5 0.0

0.2 mL/min 0.5 mL/min 1.0 mL/min

0.2

1.0

0.0

0

2

4

6

8

10

12

14

pH

Fig. 6. Effect of pH on the uptake of Cu(II) and Hg(II) by R1A at 28 C.

0

50

100

150 200 Flow rate, min

250

300

Fig. 7. Breakthrough curves at different flow rates for the adsorption process of Cu(II) and Hg(II) on R1A by column method at bed height 0.3 cm and initial concentration of 5 103 M.


264

400

1.0 Cu(II)

Cu(II) Hg(II)

0.8 300

Ct/Co

ts (min)

0.6

0.4

0.0

100

0.15 cm 0.30 cm 0.50 cm

0.2

0

10

20

30

40 50 60 Flow time, min

70

80

90

200

100

1.0 Hg(II) 0.8

0 0.0

0.1

0.2

0.3 0.4 Z (cm)

0.5

0.6

0.7

Fig. 9. The critical bed height for the adsorption of Cu(II) and Hg(II) on R1A by column method at 28 C.

obtained for the removal of the studied metal ions from their aqueous solutions.

0.6 Ct/Co

References 0.4

0.2

0.0

0.15 cm 0.30 cm 0.50 cm 0

40

80

120

160 200 240 Flow time, min

280

320

360

Fig. 8. Breakthrough curves at different bed heights for the adsorption process of Cu(II) and Hg(II) on R1A by column method at bed height 0.3 cm and initial concentration of 5 103 M.

column methods. The R1A showed higher uptake values as well as a higher binding of the studied metal ions compared with the R2A. Uptake values up to 2.38 and 1.95 mmol/g were reported for Hg (II) and Cu (II) on R1A, respectively. Application of the Langmuir model to the adsorption data indicated a higher binding of Cu (II) to the R1A compared to Hg (II) at natural pH and that the binding decreases as the temperature increases. It was found that embedding of clay particles (5% by wt.) in the resin during the polymerization process enhanced the distribution of active sites on the resin surface. Consequently, an enhancement in the kinetic and thermodynamic behavior of the resin was

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