Application of a New-Generation Complexing Agent in Removal of

Curie-Sklodowska Sq. 2, 20-031 Lublin, Poland. The paper presents the studies on removal of copper(II) and zinc(II) ions from aqueous solutions in the...
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Ind. Eng. Chem. Res. 2008, 47, 3192-3199

Application of a New-Generation Complexing Agent in Removal of Heavy Metal Ions from Aqueous Solutions Dorota Kołodyn´ ska, Zbigniew Hubicki,* and Marzena Ge¸ ca Department of Inorganic Chemistry, Faculty of Chemistry, Maria Curie-Sklodowska UniVersity, Maria Curie-Sklodowska Sq. 2, 20-031 Lublin, Poland

The paper presents the studies on removal of copper(II) and zinc(II) ions from aqueous solutions in the presence of the tetrasodium salt of polyaspartic acid carried out on commercially available, chelating ion exchangers with different functional groups which are widely applied in the recovery of heavy metal ions from industrial effluents. The research results indicate a high affinity of these resins for the zinc(II) and copper(II) ions. The sorption characteristics of each metal ion in the presence of the complexing agent onto the studied chelating ion exchangers with thiourea, aminomethylphosphonate, iminodiacetate, and polyamine groups were represented by the Langmuir isotherms quite well. Introduction In the 1980s, the first attempts were made to utilize biomineralization processes, that is, the building of skeletons or shells of crustaceans in industrial applications. It is wellknown, for example, that oysters produce a special protein-based agent that molds calcium carbonate into the characteristic shape of their shells. It has been proven that such a naturally occurring mechanism of biomineralization is preferably controlled by polyanionic proteins rich in aspartic acids and phosphoserine. Therefore, polyaspartates as inhibiting agents can be used to solve different technical problems such as those based on crystallization processes or the redeposition of minerals like alkaline earth carbonates, sulfates, or phosphates, which commonly cause hardness of water.1 It is worth mentioning that polyaspartic acid sodium salts are anion-active, water-soluble polyaminocarboxylates with a multifunctional property profile. They can be prepared by thermal polymerization of aspartic acid.2-7 Aspartic acid is produced from maleic acid anhydride by a multistep reaction. Starting with maleic acid anhydride, fumaric acid is converted to the ammonium salt of aspartic acid by a chemical or enzymatic reaction step. After hydrolysis and isolation, aspartic acid is polymerized to the primary polymerization product containing polysuccinimide structures:

Different synthetic pathways to polyaspartates described in the literature concerned methods of producing high-molecularweight, soluble, cross-linked polyaspartates from cross-linked polysuccinimide. In one preferred method, polysuccinimide is first reacted with an organic cross-linking agent, preferably an organic base containing at least two primary amine groups, to form a cross-linked polysuccinimide. The cross-linked polysuccinimide is then hydrolyzed to the cross-linked polyaspartate * To whom correspondence should be addressed. Tel.: +48 (81) 5375511.Fax: +48(81)5333348.E-mail: [email protected].

which is soluble in polar solvents, preferably water, alcohol, and so forth. Alternative method aspects are disclosed in which soluble cross-linked polyaspartates are produced in a single reaction by sequentially cross-linking polysuccinimide with the organic cross-linking agent in an aqueous reaction mixture and hydrolyzing the product to the cross-linked polyaspartate. The method of synthesis of polyaspartates determines their chemical structures, described by the molecular weights or molecular geometry. Furthermore, the properties such as dispersing activity, sequestering activity, and biodegradability are determined in the same way. Because of their unique properties they are used in a wide variety of applications such as dispersants (to reduce the deposit of insoluble magnesium and calcium salts or to stabilize oxygen-based bleaching agents), as components of laundry detergents, dishwashing, as well as water-treatment chemicals (to prevent harmful deposits of precipitated salts such as calcium carbonate), and as oil field additives. They can also be used as an alternative to conventional complexing agents. One such agent is Baypure DS 100 produced by Bayer Chemicals AG, Germany. Its typical physicochemical properties are listed in Table 1. Baypure DS 100 is a new dispersing agent having a wide range of applications, for example: • to soften water in both washing machines and dishwashers, • to improve dispersion of pigment particles in the production of paper and paints (Baypure DS 100 displays a dispersing effect comparable with the best dispersing agents in its class), • to produce latex-based coating compounds. The polyaspartic acid sodium salts can be highly effective over long periods of time in the alkaline pH range up to pH 13, and also effective in the acidic pH range. They are also stable in the presence of oxidation agents such as peroxides. Because of the above-mentioned features possessed by this modern chelating agent, it seems that soon it will be an important alternative for the traditional agents of the EDTA type. EDTA and its salts are found not to be readily biodegradable and may be classified as persistent (P) or very persistent (vP). Therefore the products (mainly detergents and fertilizers) containing EDTA and/or its salts cannot qualify for an eco-label.8-10 Large amounts of wastewaters produced from different industries contain the heavy metal ions Cd(II), Cu(II), Ni(II), Pb(II), and Cr(III) at concentrations even up to 50 g/L. Sources of these waste streams include electroplating, metal processing, refining, storage battery manufacturing, as well as pigment, cosmetics,

10.1021/ie701742a CCC: $40.75 © 2008 American Chemical Society Published on Web 04/04/2008

Ind. Eng. Chem. Res., Vol. 47, No. 9, 2008 3193 Table 1. Physicochemical Properties of Baypure DS 100a

a

properties

description

CAS No. summary formula appearance density ionicity pH mean molar mass solubility (water)

181828-06-8 [C4H4NO3Na]x clear reddish liquid approximately 1.3 g/mL strongly anionic 9.5-10.5 approximately 1.3 g/mL in any ratio

Product name is VP.OC 2401; synonym is Baypure DS 100.

and detergents manufacturing.11,12 There are many different methods for treating of such wastewaters. Current methods for wastewater treatment include precipitation, coagulation/flotation, sedimentation, flotation, filtration, membrane processes, electrochemical techniques, ion exchange, biological processes, and chemical reactions.13 Traditional treatment techniques applied for recovery of these hazardous metals produce large volumes of sludges that are difficult to handle. Additionally, the presence of strongly complexing organic agents such as EDTA, NTA, citrate, tartarate, and inorganic ligands Cl-, F-, PO43-, and so forth, makes the precipitation process infeasible and causes significant environmental problems by increasing the mobility of toxic metals to groundwater, surface water, and soil systems. Therefore, sorption is an efficient method for the removal of tracer components from waters in the presence of complexing agents. Synthetic chelating agents such as ethylenediaminetetraacetic acid (EDTA) and nitrilotriacetic acid (NTA) are widely applied in many industries because of their capability of binding and masking metal ions. Though they possess very good complexing properties, in those situations chelating agents disclose some undesirable features such as the remobilization of radionuclides and toxic heavy metals from sediments and soils. They are also resistant in conventional wastewater treatment systems. Successful biodegradation, mainly that of NTA, was observed only under laboratory conditions by special strains. For Fe(III)EDTA and Cr(III)-EDTA the only known natural attenuation is photodegradation. Consequently, there is a need to develop new reagents which should be environmentally friendly and readily biologically degraded. Besides, these modern chelating agents should possess features such as being nontoxic, harmless, with a strong ability to bind calcium and alkaline earth metals, high stability (temperature, pH, oxidants), good water solubility, easy to handle, and high efficiencyslow molecular weight and low cost. These requirements seem to be satisfied by polyaspartates (PAS), a group of acidic polyamides such as Baypure DS 100. Taking into consideration the fact that the number of commercial products including the compounds of this type is increasing, there is a need or even necessity for getting to know the possibility of the removal of heavy metal ions in the presence of biodegradable complexing factors from waters and wastewaters. This is justified by the fact that even if the complexing agents are easily biodegradable, their combinations with heavy metals are not. Although many studies have been done on the biodegradability of the new class of complexing agents,11,14-18 little information is available in the literature on the simultaneous uptake of heavy metal ions in the presence of such ligands from aqueous solutions.19-21 Removal of high concentrations of heavy metal ions is typically achieved by such technologies as precipitation, coagulation, sedimentation, and filtration. Because heavy metal ions are often present in various industrial wastewaters along with complexing agents, the heavy metal complex-bearing wastewaters require special treatment. Removal

of the anionic complexes M(II)-organic ligand is achieved after their decomposition. Also their sorption can be carried out on anion exchangers and chelating ion exchangers. In the investigations the following chelating ion exchangers were used: Lewatit TP 207, Lewatit TP 260, as well as Purolite S-930, Purolite S-940, and Purolite S-950. In order to measure the affinity of Cu(II) and Zn(II), the breakthrough curves were determined by the dynamic method. Batch experiments were also carried out in order to estimate the recovery factors (%R) as well as the concentration of analyzed metal ions at equilibrium (Qe) and at the specific time (Qt) at different metal-ligand ratios, metal concentrations, phase contact times, and pH values. Experimental Methods Materials and Resins. Copper(II) and zinc(II) chlorides (POCh, Poland) of analytical grade were used. Stock solutions (1 × 10-2 M) of the Cu(II) and Zn(II) were prepared by dissolving the exact quantity of respective salts and the required amount of Baypure DS 100 (Bayer Chemicals AG, Germany) in distilled water. The behavior of copper(II) and zinc(II) was investigated at pH values without adjustment. For individual complexes the pH values were the following: 7.0 for Cu(II)DS ) 1:1; 8.0 for Cu(II)-DS ) 1:2; 8.3 for Zn(II)-DS ) 1:1; and 9.0 for Zn(II)-DS ) 1:2. The stock solution was further diluted to the required experimental concentration. The other chemicals used were of analytical grade. The following chelating ion exchangerssLewatit TP 207 and Lewatit TP 260 produced by the Bayer AG, Germany, as well as Purolite S-930, Purolite S-940, and Purolite S-950 produced by Purolite International, Ltd.swere used in the investigations. Brief descriptions of the characteristics of these chelating resins are presented below. Lewatit TP 207 is a high-capacity, weakly acidic, macroporous cation exchange resin with the iminodiacetate functional groups; it is used for the selective extraction of heavy metal cations from aqueous solutions. It has a total ion exchange capacity of 2.0 meq/mL, a particle size of 0.61 ( 0.05 mm, and thermal stability to 313 K. Lewatit TP 260 is a macroporous weak acid cation exchange resin with aminomethylphosphonate functional groups; it is recommended by the manufacturer for the selective removal of alkaline earth metals from industrial effluents. It has a total ion exchange capacity of 2.4 meq/mL, a particle size of 0.63 ( 0.05 mm, and thermal stability to 313 K. Purolite S-930 is a macroporous polystyrene-based resin with iminodiacetate functional groups; it is designed for the removal of cations of heavy metals from industrial effluents and finds use in processes for extraction and recovery of metal ions from ores, galvanic plating solutions, and so forth. It has a total ion exchange capacity of 1.1 meq/mL (in the H+ form), a particle size of 0.3-1.0 mm, and thermal stability to 343 K. Purolite S-940 is a resin of macroporous structure with a polystyrene matrix cross-linked with divinylbenzene substituted and possesses weakly acidic aminophosphonate active groups; it is capable of fixing one or more specific cations from a larger range even from water solutions which are highly concentrated. It has a total ion exchange capacity of 20 g Ca/L at pH 9.5, a particle size of 0.425-0.85 mm, and thermal stability to 363 K. Purolite S-950 is a macroporous aminophosphonate chelating resin, designed for the removal of cations of toxic metals such as lead(II), copper(II), and zinc(II) from industrial effluents at low pH; its use may be recommended where it is necessary to remove calcium(II) or magnesium(II) in order to avoid possible

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precipitation. It has a total ion exchange capacity of 2.0 meq/ mL, a particle size of 0.3-1.3 mm, and thermal stability to 363 K. Prior to use, they were washed with 1 M NaOH and 1 M HCl to remove organic and inorganic impurities and then washed several times with deionized water. The resin was finally converted to the appropriate form. Column Studies. In order to measure the affinity of the above-mentioned Cu(II) and Zn(II) ions, the breakthrough curves were determined using 20 mL of the swollen ion exchanger in the appropriate form. The prepared solutions were passed continuously downward through the resin beds, keeping the flow rate at 0.8 mL cm-2 min-1. The effluent was collected in fractions in which the metal(II) content was determined. The weight (Dg) and bed (Dv) distribution coefficients as well as the total ion exchange capacities (Cr) of M(II) were calculated from the determined breakthrough curves according to the procedure presented earlier.22 Batch Studies. Batch experiments were performed to determine the recovery factors (%R) as well as the concentration of analyzed metal ions at the equilibrium (Qe) and at the specific time (Qt) under different metal-ligand ratios, metal concentrations, phase contact times, and pH values. The sorption of Cu(II) and Zn(II) in the presence of DS was investigated by taking the appropriate amount of chelating resin and a solution of known metal ion concentration. Metal ion concentrations used were in the range (0.1-2) × 10-3 M. The mixture was shaken in a mechanical shaker (ELPHINE type 357, Poland) at the constant temperature 298 K. After equilibrium, the concentrations of metal ions in the aqueous phase were analyzed by an atomic absorption spectrophotometer. The experiment was conducted in two parallel series. The reproducibility of the measurements was within 5%. The concentrations of chloride ions were not determined. The recovery factor was calculated from eq 1:

%R )

C 0 - Ct × 100% C0

(1)

and the resin phase concentrations of metal ions at equilibrium, Qe (mmol/g), were obtained according to eq 2:

Qe )

(C0 - Ce)V m

(2)

where C0 represents the initial concentration of M(II) in the aqueous phase (mmol/L), Ct is the concentration of M(II) in the aqueous phase at time t (mmol/L), Ce is the concentration of M(II) in the aqueous phase at equilibrium (mmol/L), V is the volume of the solution (L), and m is the mass of the ion exchanger (g). The concentration of metal ions at a specific time (Qt) was also analyzed. Sorption Isotherms. The isotherm equilibrium data were analyzed using the Langmuir and Freundlich equilibrium equations. The Langmuir isotherm is represented by eq 3:

Qe )

Q0bCe 1 + bCe

(3)

whereas the Freundlich expression is based on an exponential relationship according to eq 4:23,24

Qe ) KFCebF

(4)

where Q0 represents the Langmuir isotherm constant (mg/g of dry resin), B is the Langmuir constant (L/mg), KF is the Freundlich isotherm constant (mg/g), and bF is the Freundlich exponent (-). The constants Q0 and as well as KF and bF are characteristics of these equations and can be determined from their linearized forms. The constant bF can be expressed as 1/n, where the value of n indicates the degree of favorability of sorption. Analytical Procedure. An atomic absorption spectrometer (Varian Spectr AA-880) was used for quantitative determination of the concentration of Cu(II) and Zn(II). The AAS was equipped with a deuterium lamp, background correction, hollow cathode lamps for Cu and Zn, and an air-acetylene burner. Results and Discussion Selection of the Exchange Materials. In the preliminary studies, different chelating ion exchangers containing such functional groups as iminodiacetate (Lewatit TP 207, Purolite S-930), aminomethylphosphonate (Lewatit TP 260, Purolite S-940, Purolite S-950), thiols (Duolite GT-73), polyamine (Diaion CR 20), thiourea (Lewatit TP 214, Purolite S-920), bispicolylamine group (Dowex M 4195), and so forth were used. As follows from the obtained results, the cationic resins containing S-donor atoms (Lewatit TP-214 or Purolite S-920 as well as Duolite GT-73) with thiourea and thiol functional groups did not achieve high removal percentages for either Cu(II) or Zn(II) ions (the recovery factors less than 10% and 15%, respectively). In the cases of Dowex M-4195 and Diaion CR 20, the obtained results were also not satisfactory. Thus, in the next stages, the following ion exchangers were investigated: Lewatit TP 207 and Purolite S-930 as well as Lewatit TP 260, Purolite S-940, and Purolite S-950. These chelating ion exchangers are cation exchangers, and they can sorb cations from the solution through the exchange of H+ or Na(I). It is wellknown that they can also act as weakly basic anion exchangers. Therefore, in the process of sorption of heavy metal ions in the presence of the complexing agent, it is very important to choose the optimal experimental conditions such as metal ion/ligand ratio, metal ion concentration, and pH, as well as resin form. Effects of Dosage of Chelating Ion Exchangers. In order to find the influence of the initial amount of the chelating ion exchangers on the effectiveness of the sorption of copper(II) and zinc(II) in the presence of DS, batch sorption studies were performed. The obtained data indicate that the removal of copper(II) and zinc(II) complexes for all chelating ion exchangers increases as the amount of resin increases. In order to remove the studied metal ion quantitatively, the optimum amount of resin was found as 0.3 g per 50 mL of solution. Effect of Contact Time. The investigations of copper(II) and zinc(II) sorption by the static method depending on the phase contact time, were carried out in the 0.001 M M(II)-0.001 M DS and 0.001 M M(II)-0.002 M DS systems using the selected ion exchangers. The exemplary values of the recovery factors (%R) of the complexes determined on Lewatit TP 260 and Lewatit TP 207 are presented in Figures1 and 2. These figures indicate that the concentration of the remaining copper(II) and zinc(II) in the solution continuously decreases with time until about 60 min, when the equilibrium is reached. As follows from the comparison of the obtained results, the recovery factors assume the values in the range from 60% to 100% and they are

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Figure 1. Effect of the phase contact time on the sorption of Cu(II) and Zn(II) with DS in the M(II)-DS ) 1:1 and M(II)-DS ) 1:2 systems on Lewatit TP 260.

Figure 2. Effect of the phase contact time on the sorption of Cu(II) and Zn(II) with DS in the M(II)-DS ) 1:1 and M(II)-DS ) 1:2 systems on Lewatit TP 207.

much more differentiated for the ion exchangers in the Lewatit group than for those in the Purolite group. Additionally, it was noticed that the removal of the abovementioned ions decreases as the M(II)-DS ratio increases. Assuming formation of cationic and neutral soluble complexes between metal ions M(II) and polyaspartic acid, the appropriate reactions can be written according to eqs 5 and 6:

M2+ + HL a [ML]+ + H+

(5)

M2+ + 2HL a [ML2] + 2H+

(6)

where M represents the metal ion, and HL represents the neutral form of polyaspartic acid. The zinc(II) complexes exhibit higher affinity than the analogous copper(II) complexes. As follows from the manufacturer data,7 polyaspartic sodium salts exhibit moderately high stability constants only for iron (log K ) 10.0 for Fe(II) and log K ) 18.5 for Fe(III)), whereas for other metal ions they are in the range 1.7-7.5. In the case of studied heavy metal ions, the stability constant for copper(II) complexes with DS is higher than for the zinc(II) ones (log K ) 4.80 for Cu(II) and log K ) 2.2 for Zn(II)). The obtained data indicate that the functional groups of chelating ion exchangers compete for complexes; therefore, the complexes with less stability are sorbed more easily.

Figure 3. Effect of pH on the sorption of Cu(II) with DS in the M(II)DS ) 1:1 and M(II)-DS ) 1:2 systems on Lewatit TP 260.

Figure 4. Effect of pH on the sorption of Cu(II) with DS in the M(II)DS ) 1:1 and M(II)-DS ) 1:2 systems on Lewatit TP 207.

Effect of pH. The effect of pH is an important parameter affecting the ion exchange process. The polyaspartic acid has free carboxylic acid and amine groups. The protonation of secondary amine groups of DS and carboxylic groups occur at pH e 3. At pH > 3, ionization of the carboxylic group is observed and, in the case of bivalent metal ions, double interaction take place. Therefore, the experiments to establish the pH effect on the sorption of copper(II) and zinc(II) ions in the presence of DS using the above-mentioned ion exchangers in the range 3-9 were carried out. The exemplary plots of Cu(II)-DS complex sorption for Lewatit TP 260 and Lewatit TP 207 are presented in Figures3 and 4. It was shown that Cu(II) sorption is almost constant when the pH increases from 3.0 to 6.0. However, in the case of the M(II)-DS ) 1:1 system for the pH above 6.0, the rate of sorption increases. But for the Cu(II) complexes with DS in the M(II)-DS ) 1:2 system, such a pH effect has not been reported. As follows from the literature data, the aminomethylphosphonic acid chelating groups are potentially tridentate ligand, having two bonding sites at a phosphonic acid group and one coordination site at the secondary nitrogen atom.25-28 The sorption of heavy metal ions can proceed by their coordination interaction and then through their ionic interaction. On the other hand, the presence of various functional groups in the polymer phase affects the acid-base equilibrium as well as sorption properties of the ion exchanger. The trend of change caused by the presence of functional groups depends on the quantitative ratio of acid-character groups and base-character ones and their position toward each other. Depending on the pH, aminomethylphosphonic acid chelating groups occur in the following forms:

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The ion exchangers containing such groups are characterized by large selectivity toward heavy metal ions, and their sorptive properties are determined by the extent of phosphonic group ionization. This is due the electron-acceptor effect of the cationic center tN or tPd through the alkyl fragment. As follows from the literature, lengthening of the alkyl fragment of the aminoalkylphosphonic group leads to an insignificant increase of sorption capacity toward heavy metal ions. The presence of a methylene group increases the electron density on the nitrogen atom of the amine group which promotes its protonation:

The most favorable mode of chelation when the pH increases into the weak acid region is formation of a 4-membered ring. In this case, these functional groups can act as tridentate ligands and the structure of formed complexes can be as follows:

In the acidic conditions, because of strong protonation the amino-nitrogen atom does not participate in the bond formation and complexes without amine group contribution can also be formed. The most frequent structure is as follows:

In analyzing ion exchange equilibrium, it is necessary to take into account not only the nature of the resin and the exchanged cation but also the nature of the anion, especially when the simultaneous process of their sorption is carried out. As follows from the studies, in the case of sorption of Cu(II) and Zn(II) ions not only the ion exchange mechanism but also the formation of coordination bonds must be taken into consideration. The percentage of sorption of studied metal ions in the presence of DS depends on the strength of the metalpolyaspartate complexes. As follows from the literature data the strength of complexation decreases in the following order: Cu(II) > Pb(II) ∼ Co(II) > Zn(II) > Mn(II). Because the formed complexes are relatively weak,20 the bond M(II)-DS is broken and then the complex in the ion exchangers phase is formed, as evidenced by high values of distribution coefficients. It is also in agreement with the values of the stability constants of copper(II) and zinc(II) complexes with aminomethylphosphonic acid (log K ) 8.12 for Cu(II) and log K ) 2.88 for Zn(II)).26 In the case of Lewatit TP 207, depending on the pH values the iminodiacetate groups occur in the forms presented below:29,30

In solutions with a pH about 2 (or less), both carboxylic groups and nitrogen atom occur in the protonated form. As a result, the chelating ion exchanger can behave as a weakly basic anion exchanger. At higher pH (∼12), both carboxylic groups are deprotonated and the ion exchanger can behave as a typical cation exchanger. However, at intermediate pH values, the resin behaves in an amphoteric way. Under such conditions, nitrogen is protonated and at least one of the carboxylic groups is dissociated. For Lewatit TP 207, attention should also be paid to the possibility of coordination bond formation. This is enabled by the presence of three donor atoms with a lone pair of electrons. As follows from the obtained results, the complexes of copper(II) and zinc(II) with DS probably participate in the sorption process. Effect of Metal(II) Concentration. In order to establish heavy metal sorption at different concentrations, the batch studies were carried out in the copper(II) and zinc(II) concentration range from 0.25 to 2 × 10-3 M at a pH of 7.0. The results in the M(II)-DS ) 1:1 system for Lewatit TP 260 and Lewatit TP 207 show that the copper(II) and zinc(II) sorption rate slightly increased from 80 to almost 100% with an increase in its initial concentration up to 2 × 10-3 M. For quantitative estimation of the amount of Cu(II) and Zn(II) sorbed, the loading capacities were calculated and are given in Table 2. Sorption Isotherms. The Langmuir and Freundlich isotherms are those most commonly used to describe the sorption characteristics of sorbents and ion exchangers.21,22 While the Freundlich isotherm describes the sorption characteristics of the resin when nonideal sorption on a heterogeneous surface as well as multilayer sorption take place, the Langmuir isotherm is based on the assumptions that sorption can occur only at a fixed number of definite localized sites and that each site can hold only one molecule (monolayer). The values of the Langmuir constants are related to the physical properties of the system: Q0 reflects the solute capability for sorption, and b is related to the energy of sorption. The Freundlich constant KF expresses the sorbent capacity, and bF is the heterogeneity factor. On the basis of the Freundlich constant, bF (expressed also as 1/n), sorption can be classified as favorable or unfavorable. Therefore, the smaller values of this constant can indicate a weak bond between the ion sorbed and the sorbent as well as the heterogeneous nature of the sorbent surface. However, high values of KF indicate a large rate of removal. Examples of the Langmiur isotherm and its linearized form for zinc(II) with DS on Lewatit TP 260 are presented in Figures 5 and 6. The isotherm constants obtained from the linearized plots of the Langmuir and Freundlich equations and the values of correlation coefficients (R2) for the copper(II) and zinc(II) complexes with DS sorbed on Lewatit TP 207 and Lewatit TP 260 are presented in Table 3. For studied metals the experimental data correlated better with the Langmuir model. The calculated sorption capacities from the Langmuir equations for copper(II) and zinc(II) were compared with the measured values. Column Studies Results. In order to determine optimal conditions of sorption of copper(II) and zinc(II) complexes with

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Figure 5. Equilibrium isotherm for loading of Zn(II) in the M(II)-DS ) 1:1 systems on Lewatit TP 260.

Figure 6. Linearized form of the Langmuir isotherm for Zn(II) in the presence of DS in the M(II)-DS ) 1:1 systems on Lewatit TP 260. Table 2. Loading Capacities (mmol/g) of Lewatit TP 260 and Lewatit TP 207 for Cu(II) and Zn(II) system Cu(II)-DS ) 1:1 Zn(II)-DS ) 1:1 Cu(II)-DS ) 1:1 Zn(II)-DS ) 1:1

Figure 7. The breakthrough curves of Cu(II) and Zn(II) with DS in the M(II)-DS ) 1:1 and M(II)-DS ) 1:2 systems on Lewatit TP 260.

Figure 8. The breakthrough curves of Cu(II) and Zn(II) with DS in the M(II)-DS ) 1:1 and M(II)-DS ) 1:2 systems on Lewatit TP 207.

loading capacity Lewatit TP 260 0.18 0.23 Lewatit TP 207 0.17 0.21

Table 3. Values of the Parameters in the Langmuir and Freundlich Equations for Cu(II) and Zn(II) with DS on Lewatit TP 260 and Lewatit TP 207 Langmuir parameters Q0 (mg/g-dry resin)

b (L/mg)

Freundlich constants R2

KF (mg/g)

n (-)

R2

Cu(II) Zn(II)

13.10 14.82

Lewatit TP 260 1.19 0.9838 3.51 0.9547

5.24 10.30

3.34 2.18

0.531 0.9632

Cu(II) Zn(II)

9.83 13.64

Lewatit TP 207 3.09 0.9693 5.23 0.9662

4.83 9.09

4.65 2.61

0.6320 0.9320

DS by the dynamic method, the breakthrough curves in the 0.001 M M(II)-0.001 M DS and 0.001 M M(II)-0.002 M DS systems were determined. The plots of concentration C/C0 versus volume of effluent (mL) (Figures 7-10) show the effect of the molar ratio of copper(II) or zinc(II) concentration to DS on sorption effectiveness on Lewatit TP 260 and Lewatit TP 207 as well as on Purolite S-950 and Purolite S-940. The effect of the form of the ion exchanger was also taken into consideration (not presented). As follows from the obtained results, the zinc(II) complexes with DS exhibit a higher affinity compared to the copper(II)

Figure 9. The breakthrough curves of Cu(II) and Zn(II) with DS in the M(II)-DS ) 1:1 and M(II)-DS ) 1:2 systems on Purolite S-950.

complexes for chelating ion exchangers. This is the reverse tendency of affinity compared with that observed for polystyrene anion exchangers.31 The obtained results were also confirmed by the calculated distribution coefficients as well as by sorption capacities of ion exchangers (Table 4). As follows from the research, the chelating ion exchangers, according to their applicability in sorption of the Cu(II) and Zn(II) complexes with DS in the 0.001 M M(II)-0.001 M DS and 0.001 M M(II)-0.002 M DS systems by the dynamic method, can be put in the following order: Lewatit TP 260 > Lewatit TP 207 > Purolite S-950 > Purolite S-940 > Purolite S-930. Taking into account the effect of the form of ion exchangers, it was found that the Lewatit TP 207 in the H+ form is the more effective in sorption of the zinc(II) complexes with DS

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erodispersive as well as isoporous or macroporous) may affect properties of chelating ion exchangers. Literature Cited

Figure 10. The breakthrough curves of Cu(II) and Zn(II) with DS in the M(II)-DS ) 1:1 and M(II)-DS ) 1:2 systems on on Purolite S-940.

Table 4. Weight (Dg) and Volume (Dv) Distribution Coefficients as Well as the Total (Cr) Ion Exchange Capacities (mg/mL) for Cu(II) and Zn(II) in the Presence of DS on Lewatit TP 260 and Lewatit TP 207 M(II)-DS system

Dv

Cr

Cu(II)-DS ) 1:1 Zn(II)-DS ) 1:1 Cu(II)-DS ) 1:2 Zn(II)-DS ) 1:2

Lewatit TP 260 2006 3920 1308 2982

Dg

770 1504 502 1144

64 107 70 80

Cu(II)-DS ) 1:1 Zn(II)-DS ) 1:1 Cu(II)-DS ) 1:2 Zn(II)-DS ) 1:2

Lewatit TP 207 2317 2968 1726 2382

957 1226 713 984

61 83 40 68

than in the Na+ form, which confirms that the bond M(II)-DS is broken and the complex in the resin phase is formed. In this part of the research, the effect of a regenerating agent was also investigated. The exhausted chelating ion exchangers were completely regenerated by 1 M HCl. In the case of polystyrene anion exchangers such as Lewatit MonoPlus M 500, the regeneration step was achieved by 1 M NaCl.31 In summary, it can be stated that the research results indicate a high affinity of the chelating ion exchangers Lewatit TP 260 and Lewatit TP 207 for zinc(II) and copper(II) in the presence of polyaspartic acid sodium salt. Lewatit TP 260 is the example of the ion exchanger applicable for separation and preconcentration of the d-electron metal cations whose functional groups not only undergo ionization but also carry electron pairs. Sorption of metal ions on these ion exchangers proceeds due to simultaneous formation of coordination and ionic bonds. Differences in the affinity of Zn(II) and Cu(II) complexes with DS for chelating ion exchangers in individual systems are probably due to the structure of these complexes and their stability. As follows from the studies, sorption ability of chelating ion exchangers is also affected by the kind of functional groups and their positions toward each other, the kind of matrix (skeleton), and the form of the functional group. As for the chelating ion exchangers including the same functional groups produced by different manufacturers (for example Lewatit TP 260 and Purolite S-940 or Purolite S-950, etc.), their different behavior toward various metal ions can be explained by the many ways of their synthesis. The manufacturers do not give detailed methods of the synthesis, and often the ion exchangers presented in brochures are described as monofunctional but, in fact, they prove to be polyfunctional. Moreover, different skeleton structures (monodispersive, het-

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ReceiVed for reView December 21, 2007 ReVised manuscript receiVed February 11, 2008 Accepted February 18, 2008 IE701742A