ELSEVIER Desalination 180 (2005) 271-276

DESALINATION

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Removal of metal ions in aqueous solutions by organic polymers: use of a polydiphenylamine resin

E1 Mostapha Jouad a, Fr6d6rique Jourjon b, Georges Le Guillanton a*, Driss Elothmani b ~Electrochimie et Environnement, Centre d'Etude et de Recherche sur les Ecosystdmes Aquatiques (CEREA),

Universit~ Catholique de l'Ouest, BP 10808, 49008 Angers Cedex 0I, France Tel. +33 (2) 41 81 66 58; Fax: +33 (2) 41 81 65 37; email: gleguill@uco.fr

bLaboratoire GRAPPE, Ecole Sup~rieure d'Agriculture d 'Angers, BP 30748, 49007 Angers Cedex 01, France

Received 29 September 2004; accepted 27 December 2004

Abstract

Adsorption ofNi(II), Cu(II), Zn(II), Pb(II) and Cd(II) ions on a polydiphenylamine resin prepared at a strongly oxidizing controlled potential of 3.2 V (vs. ECS) was studied in aqueous solutions. The optimum sorption conditions were determined. The optimum pH for the removal of metal ions was between 4 and 6 for Ni(II), 6 for Cu(II) and Pb(II) and 5 for Zn(II) and Cd(II). The total sorption capacity of the resin was 57.3 mg g-1 for Ni(II), 23 mg g-~ for Cu(II), 36.9 mg g-~ for Zn(II), 19 mg g-t for Pb(II) and 24.5 mg g-l for Cd(II). The sorption capacity was compared with other conventional chelating polymers. The sorption kinetics was fairly rapid, as apparent from the loading half time (t~/2) values, indicating a better accessibility of the chelating sites. The study of the selectivity of the metal ions in the binary solutions shows that the resin presents a higher affinity for the ions of nickel (II).

Keywords: Polydiphenylamine resin; Sorption capacity; Sorption kinetics; Selective property; Removal; Metallic trace elements

1. Introduction

With growing pressures on water resources and the increase in toxic pollutants entering reservoirs, rivers and groundwater, the supply of high-quality potable water and treatment of wastewater to regulatory standards present unique challenges for water authorities during the corn-

*Corresponding author.

ing years. A specific concern is the presence of toxic transition and heavy metals such as copper, zinc, cadmium, lead and mercury. These metals can be introduced into aquatic systems through effluent discharges from various industrial opera- tions including mining, chemicals manufacture, electroplating and distilling and brewing [1,2]. Although source reduction and efficient waste management programmes are the preferred long-

0011-9164/05/$- See front matter © 2005 Elsevier B.V. All rights reserved

doi: 10.1016/j.desal.2004.12.039

272 E.M. Jouad et al. / Desalination 180 (2005) 271-276

term solutions, upgrading existing treatment systems and the implementation of new and novel technologies will continue to play an important role.

Numerous processes exist for removing dis- solved metals, such as coagulation and chemical precipitation [3], slow sand filters [4,5], mem- brane technologies [6,7], adsorbing natural pro- ducts [8-13] and adsorbing resins [14-16]. With regard to this latter process, several studies were devoted to the formation of polydiphenylamine and their conducting properties [17-20]. How- ever, till now no studies have been reported concerning there adsorbing properties.

Given the significant quantity of this polymer resin formed according to experimental condi- tions as reported by Elothmani et al. [20], we have continued this study and herein report the results of adsorbent and selective properties on Ni(II), Cu(II), Zn(II), Pb(II) and Cd(II) in aque- ous solution.

2. Experimental

2.1. Apparatus and reagents

The concentration of metal ions Ni(II), Cu(II), Zn(II), Pb(II), and Cd(II) in solution was deter- mined by flame atomic absorption spectroscopy (AAS) (Perkin Elmer, model 3100). The ope- rating conditions of the AAS instrument (pre- viously standardised) for the determination of metals are presented in Table 1. The pH measure- ments were made with a Tacussel pH meter (model PHN 81) with a glass electrode (Tacussel) calibrated with Metrohm Herisau buffers. Batch equilibration studies were carried out using a mechanical shaker (Bioblock).

The diphenylamine, 1,2-dichloroethane, tri- chloroacetic acid, triethylamine and supporting electrolyte tetraethylammonium perchlorate were used as received (Fluka). All other chemicals used in the present work were of analytical grade from E. Merck or Sigma-Aldrich.

Table 1 Operating parameters used for recording AAS for dif- ferent metal ions with a flame type of air-acetylene (oxidizing)

Metal ion HC lamp (mA) Wavelength (nm)

Ni(II) 4.0 351.5 Cu(II) 15.0 324.7 Zn(II) 15.0 213.9 Pb(II) 8.0 283.3 Cd(II) 5.0 228.8

Nickel (II) (1000 #g ml~), copper (II) (1000/zg ml-~), zinc (II) (1000 #g ml-~), lead (II) (1000 #g ml -~) and cadmium (II) (1000/zg ml -~) standard stock solutions were prepared by dissolving nickel (II) nitrate, copper (tI) bromide and sulfate salts of zinc (II), lead (II) and cadmium (II) in deionized water. Deionized water was also used in all dilutions and in the preparation of standards used in calibration.

The buffer solutions for pH 1-3 using hydro- chloric acid (0.2 M), glycine (0.2 M) for pH values between 3-5 using acetic acid (0.2 N); sodium acetate (0.2 N) and for pH between 5-8 using disodium hydrogen phosphate (0.06 M), potassium dihydrogen phosphate (0.06) were prepared and used [20].

2.2. Preparation o f the sorbent

The black polydiphenylamine resin PDPA was obtained as previously described [20] by elec- trolysis of the diphenylamine at a strongly oxi- dizing controlled potential of 3.2 V (vs. ECS) in 0.2 M (CzHs) 4 C104-1,2-dichloroethane in the presence of trichloroacetic acid on a platinum electrode. This type of electrolysis allows the formation of significant quantities of PDPA (the yield is practically quantitative compared to the monomeride mass present in solution). The polymer obtained (5 g) was dedoped to eliminate perchlorate ions using a treatment with a large

E.M. Jouad et al. / Desalination 180 (2005) 271-276 273

amount oftriethylamine (25 ml) during 2 h; then it was filtered, washed with deionized water and finally dried in vacuum over silica gel for 24 h. In order to increase adsorbing specific surface, the matrix obtained was milled and sifted. Only the particles which were smaller in size than 150 #m were retained for this study.

2.3. Procedure

The batch equilibration technique was used to determine the optimum sorption conditions such as pH, adsorption time, capacity of the sorbent and its selective property. The chelating resin was equilibrated with a suitable amount of metal ions, and the unextracted metal ions were determined by AAS.

The amount of metal ions adsorbed on the solid phase was determined by the equation

X - Y NI: Z

whereXis the initial amount of metal ion, Yis the amount of metal ions in the supernatant, Niis the amount of metal ion adsorbed and Z is the amount of chelating resin. The sorbed metal ions were eluted with 1 N HC1/HNO 3, and the metal con- centration in the eluent was determined by AAS.

2.4. Optimum p H o f metal ion uptake

The optimum pH of metal ion uptake was determined by the batch equilibration technique. An excess metal ion (50 ml, 50 /zg m1-1) was shaken with 100 mg of resin for 2 h. The pH of metal ion solution was adjusted prior to equili- bration over a range of 2-8 with buffer solution. The resin was filtered off and the amount of metal ion remaining in the filtrate was determined using AAS. Adsorption experiments were carried out in triplicate to determine the precision of the method.

2.5. Resin capacity

The total sorption capacity of the resin was determined by shaking an excess of metal ion solution (100 ml, 50 #g m1-1) with 100 mg resin for 24 h at optimum adsorption pH at room temperature (24°C) in a mechanical shaker to ensure complete equilibrium. The resin was filtered off and the concentration of metal ion in the filtrate was determined using AAS.

2.6. Sorption kinetics

The rate of loading of metal ions on the resin was determined under the conditions described below. 50 ml of metal ion solution (100/,tg ml-1) was stirred with 100 mg of the resin at 24°C in a mechanical shaker. An aliquot of 5 ml solution was removed at predetermined intervals for analysis by AAS, and the amount of metal ions loaded on the resin phase was calculated. The loading half time, tv2, i.e., the time required to reach 50% of the resin total loading capacity, was estimated from the resulting isotherm.

2.7. Resin stability test

The following conditions were used for the resin stability study: 100 mg of the resin was stirred with 100 ml of a 50 ppm metal solution for 6 h at 24°C. The elution operation was carried out by shaking the resin with 20 ml of the eluent for 4 h to ensure complete equilibration. The metal content in the eluent was determined by AAS.

2.8. Selective property

The study of this property was carried out on the Ni-Cu, Ni-Pb and Cu-Pb binary solutions at pH 6 and on the Ni-Zn, Ni-Cd and Zn-Cd binary solutions at pH 5, under the following conditions. The concentration of each metal in the binary solution was 50 #g ml -~. The binary solution was stirred with 100 mg of the resin at room

274 E.M. Jouad et al. / Desalination 180 (2005) 271-276

temperature in a mechanical shaker for 24 h. The resin was filtered off and the concentration of each metal ion in the filtrate was determined using AAS.

3. Results and discussion

3.1. Sorption o f metal ions as a function o f p H

The sorption of metal ions viz Ni(II), Cu(II), Zn(II), Pb(II) and Cd(II), on the polydiphenyl- amine resin was carried out at different pH by batch equilibration and is shown in Fig. 1. The degree or percentage of metal sorption was calculated by measuring the metal content before and after the chelation. The adsorption of metal ions increases with increasing pH, reaching a limiting value in each instance followed by a decrease in adsorption beyond the limiting value. Optimal adsorption is noted at pH 5 for Zn and Cd and at pH 6 for Cu and Pb. On the other hand, the adsorption of Ni is effective between pH 4 and 6. This is explained by the stability of the complexes formed between metal and amino groups of the resin at these pH values. For the explanation of the pH effect, see Eiden et al. [9] and Sturm and Hesse [22].

3.2. Resin stability tests

The resin stability was tested by subjecting the resin to several loading and elution batch operations. The sorbent is highly stable and does not undergo degradation to any significant extent and, therefore, can be used repeatedly. There was no decrease in sorption capacity under static conditions, even after ten cycles of operation.

3.3. Total sorption capacity

The capacity of the resin is an important factor to determine the amount of resin required to remove a specific metal ion quantitatively from the solution. The loading capacity was deter-

Table 2 Loading capacity of the resin

Metal Optimum Capacity Capacity ion pH (mg g-1 resin) (mmol g-1 resin)

Ni(II) 4-6 57.3 0.976 Cu(II) 6 23.0 0.362 Zn(II) 5 36.9 0.564 Pb(II) 6 19.0 0.178 Cd(II) 5 24.5 0.217

mined at optimum pH and the results expressed in mg g-1 and mmol g-1 of the resin are presented in Table 2. The observed sorption capacity during the present investigation for Cu(II), Zn(II), Pb(II) and Cd(II) is limited in comparison with usual amberlite XAD resins such as XAD-4 (styrene- divinylbenzene copolymer) [21]. In the case of Ni(II) this capacity is relatively higher than the values given in the literature [21 ].

3.4. Sorption kinetics

The kinetics of resin metal interaction is of considerable importance if the resin is to be used in a dynamic system such as a packed column and a flowing stream. To determine the rate of load- ing ofNi(II), Cu(II), Zn(II), Pb(II) and Cd(II) on the resin, batch experiments were carried out at optimum pH for the respective metal ions at room temperature. The results are reported in Fig. 2. The loading half-time, defined as the time required to reach 50% of the resins total loading capacity, was estimated from the curves and the results are reported in Table 3. In spite of the limited capacity of adsorption on this resin, the latter showed remarkable kinetics of adsorption as compared to kinetics of other materials as reported in the literature.

The polydiphenylamine resin developed dur- ing the present investigation was found to be very effective for the trace removal of heavy metals, with fast kinetics as compared to other chelating

E.M. Jouad et al. / Desalination 180 (2005) 271-276 275

bb

o

&

0

%

70

60

50

40

30

20

t0

0 - -

1

BNi

GCu

BZn

EPb

g C d

2 3 4 5 6 7 8 pH

Fig. 1. Effect of pH on metal sorption.

110

loo

~ 90

~ 80 ~

70-

60-

.g ~ 40-

I 30.

~ 20-

10-

ol

/ f / / / --,--=,i) / / / /

t / / / / -40-- Ni(II)

5 10 15 20 25 30

Time (min)

Fig. 2. Effect of shaking time on metal sorption.

resins. With the exception of Pb (II), it appears that there is a relation between the kinetic of adsorption and ionic radius of the metallic ion. Which is simply that the uptake of metal increases with increasing of ionic radius. This can be observed in Table 3. However, at the moment there is no clear explanation of this phenomenon.

3.5. Selective property

The selectivity by the resin was studied when two metals present a maximum of adsorption at

the same pH. For this study, batch experiments were carried out at pH 6 for Cu-Pb, Cu-Ni and Pb-Ni binary solutions and at pH 5 for Zn-Cd, Zn-Ni and Cd-Ni binary solutions. These opti- mal pH values were selected in accordance with the results reported in Table 3. Table 4 shows the percentage of metal ions adsorbed on the resin in each binary solution.

At both of these values of pH, the resin exhibited a strong affinity for Ni compared to the rest of the metals. This can be explained by stability of complexes formed between nickel (II)

276 E.M. Jouad et al. / Desalination 180 (2005) 271-276

Table 3 Loading half-time and ionic radius for metal ions

Metal ion Load half-time Ionic radius (min) (/~)

Nickel (II) 8.8 0.69 Copper (II) 7.9 0.73 Zinc (II) 7.5 0.74 Lead (II) 4.7 0.64 Cadmium (II) 3.1 0.95

Table 4 Percentage of metal ion adsorbed in different binary solutions

pH Binary solution Ions adsorbed (%)

5 Ni-Zn Ni(II) 92.11

Zn(II) 25.70

Ni-Cd Ni(II) 95.05

Cd(II) 15.80

Zn-Cd Zn(II) 93.87

Cd(II) 74.44

Ni-Cu Ni(II) 89.70

Cu(II) 34.20

Ni-Pb Ni(II) 95.32

Vb(II) 19.50

Cu-Pb Cu(II) 87.78

Pb(II) 29.94

and the resin at these pH. Considering the Cu-Pb binary solution, a better selectivity is noted be- tween Cu and Pb than between Cd and Zn in the Cd-Zn binary solution.

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