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Synthesis and characterization of a new guar gum 4-hydroxybenzoic acid resin and its use for the separation of heavy metal ions in industrial effluents.

INTRODUCTION

Environmental pollution due to toxic heavy metals in water is a major global problem. Heavy metals cannot be degraded or destroyed; hence they are persistent in all parts of the environment.

The reduction amount of these metals from effluents to a permissible limit before discharging them into streams and rivers is very important for human health and environment. Therefore, separation of these metals in natural water at trace level is of paramount importance both for water purification and analysis. The complete removal of heavy toxic metal ions that is incompatible with the biological system requires expansive treatment to turn again useful as domestic waters. Various methods have been developed for the removal of these metal ions from aqueous systems such as solvent extraction (1), precipitation and coprecipitation (2), electrochemical reduction (3), chemical and biosorption (4), adsorption (5-7), precon-centration (8), reverse osmosis (9), and ion exchange (1013). Most of these processes may be ineffective, extremely expensive, or generate secondary pollution. In recent years, the ion exchange process has received much attention and became one of the more popular methods for the removal of heavy metal ions from the wastewater because of its competitive and effective process. Though numerous adsorbents have been reported for the removal of toxic metal ions, such as chitin (14), chitosan 115). starch (16), cellulose (17-21), tamarind (22), cyclodextrin (23), and activated carbon (24) which are not only eco-friendly and cost-effective but are effective also in remediation of common effluents present in the wastewater. Many studies have shown the functionalization of a polymeric matrix with different chelating functionalities for metal ions removal or separation (25), (26).

Guar gum is a galactomannan biopolymeric material isolated from the endosperms of Cyantopsis tetragonalo-bus, which is native to northwestern parts of India (27). A polysaccharide consisting of linear chains of mannose with 1[beta](right arrow) 4 linkages to which galactose units are attached with 1[alpha] (right arrow) 6 linkages. The ratio of mannose to galactose is 2:1. The structure of guar gum is shown in Fig. 1.

The guar gum may be potentially used as an adsorbent; however, its water solubility does not permit this under aqueous condition. Its stability (28) and solubility as well as its sorption capacity can be altered through functionali-zation by organic group (29) and chelating agent (30).

Chauhan et al. studied the synthesis and characterization of novel guar gum hydrogels and their use as Cu(II) sorbent (31). A hydrophilic polysaccharide matrix of guaran has been used for the preparation of some new chelating resins, i.e., guaran sulfonic acid cation exchanger (32) glycine hydroxamate in guaran (GH-G), acetic acid hydroxamate in guaran (AAH-G), and imino-diacetic acid dihydroxamate in guaran (IDAAH-G) after its crosslinking with epichlorohydrin (33). Water insoluble copolymer of guar gum such as poly(methacrylate) grafted guar gum (34) may be potentially used as adsorbent in the aqueous medium successfully.

The ion exchangers based on guar gum powder is hydrophilic and biodegradable, whereas other ion exchangers prepared from petrochemical product are not hydrophilic and biodegradable. Due to rising prices of petroleum products the guar gum powder has been selected for development of guar gum 4-hydroxybenzoic acid (GHBA) resin, whose cost is very low, because it is locally available in large quantities from agriculture resources and these biopolymers are eco-friendly.

Present work was undertaken to study the synthesis and characterization of GHBA resin and its applications for removal and recovery of toxic metal ions from effluent of Paradise Steel Industry, Jodhpur, India in the form of batch and column process. The effects of various adsorption conditions, such as pH, temperature, treatment time, agitation speed, adsorption dose, and flow rate were also investigated.

MATERIALS AND METHODS

Chemicals and Sample

The chemical used in the present work were, e.g., guar gum powder (Ases Chemical Works, Jodhpur, India), epichlorohydrin (Aldrich, USA), 4-hydroxybenzoic acid (LOBA Chemic Pvt. Ltd., Mumbai, India), sodium hydroxide (Sarabhai M. Chemicals, Baroda, India), and dioxane (E Merk, Mumbai, India). Metal ions solutions were prepared by dissolving appropriate amount of metal salts in double distilled water. The effluent of Paradise Steel Industry, Jodhpur (Rajasthan) has following characteristic features as given in Table 1.

TABLE 1. The characteristic features of effluent of Paradise
Steel Industry. Jodhpur.

Appearance:
Turbid

Color: Dirty
brown

pH: 5.4

Total hardness:
885 ppm

Metal ion        [Fe.sub.2+]  [Cu.sub.2+]  [Zn.sub.2+]


concentration           1.28         0.72         5.12
(in ppm)

Appearance:
Turbid

Color: Dirty
brown

pH: 5.4

Total hardness:
885 ppm

Metal ion        [Pb.sub.2+]  [Cd.sub.2+]  [Mg.sub.2+]


concentration           0.82         0.26        116.3
(in ppm)

Appearance:
Turbid

Color: Dirty
brown

pH: 5.4

Total hardness:
885 ppm

Metal ion        [Ca.sub.2+]

concentration          163.4
(in ppm)

Other anions (ppm): fluoride = 0.78; sulfate = 504; cyanide = 0.05


Apparatus

An atomic absorption spectrophotometer (Perkin--Elmer, MA, model 2380) was used for quantitative determination of trace metals and an FTIR instrument was used (Varian, Palo Alto, CA, model 640) for determination of IR spectra. Thermal stability of the synthesized resin was determined by thermogravimetry (Varian, Palo Alto, CA, model 951). Elemental analysis (CHNO) was performed with an elemental analyzer (Carlo Erba, Stanford, CA, model 1160).

Synthesis of Guar Gum 4-Hydroxyhenzoic Acid Resin

Synthesis of GHBA resin accomplished in the following steps is shown in Fig. 2.

Preparation of Epoxypropyl Ether of Guar Gum. About 162 g of guar gum (1.0 mol) were suspended in dioxane, stirred the reaction mixture on a magnetic stirrer, and 5 ml of 50% aqueous NaOH solution were added followed by 9.25 g (0.1 mol) of epichlorohydrine and the mixture was stirred for at least 5 hr at 60[degrees]C. The product epoxy propyl ether of guar gum was filtered under vacuum and washed with methanol to remove the impurities and dried.

Preparation of 4-Hydroxybenzoic Acid Derivative of Guar Gum. Epoxypropyl ether of guar gum was then allowed to react with 13.8 g (0.1 mol) of 4-hydroxy-benzoic acid with stirring and the reaction was continued for another 4 hr at 60[degrees]C. The product so formed was filtered under vacuum and washed with aqueous methanol, containing few drops of HC1 to remove any inorganic impurities and to neutralize excess of NaOH and finally washed with methanol and dried. The yield of the GHBA resin is 184.14 g. The reaction scheme for the synthesis of GHBA resin is shown in Fig. 2.

Water Washing of lon-Exchange Resin

The resins were washed with diluted HCI to create the hydrogen form, and then the hydrogen form of the resin was washed with double distilled water to remove all the excess acid. The dried material at 378 K was used for further experimental work.

Column Experiment

In the column experiment, a glass tube with 1.6 cm internal diameter and 20 cm height, packed with 8.0 cm of resin (8.5 g) was used. About 50 ml of the sample metal ion solution was passed through the column at a flow rate of 2.0 ml per minute. The flow rate was controlled by a peristaltic pump. The column was washed with 20 ml of deionized water and the washing was rejected. The metal ions were eluted quantitatively with different strength of acids.

Determination of Distribution Coefficient

The distribution coefficients ([K.sub.d]) of metal ions on resin were determined by batch method. In all cases for the determination of [K.sub.d], 50 ml sample solution was taken in a conical flask. The pH was adjusted by different amount of acetic acid and sodium acetate. About 50 mg of GHBA resin were added to the solution and stirred on a magnetic stirrer for 2 hr and the contents were equilibrated. The solution was filtered through Whatman filter paper no. 40. The residue on the filter paper was equilibrated with 4 N HCI and the solution was filtered through Whatman filter paper no. 42.

The toxic metal ion concentration in the filtrate as well as in the residue was estimated using atomic absorption spectrophotometer. The calibration curves for different metal ions were plotted, by analyzing a series of standard solutions of metal ions using atomic absorption spectrophotometer (AAS). The different wavelengths of main resonance line and air acetylene flame were used for the estimation of various metal ions. The concentration of metal ion in filtrate was determined by the calibration curves and the percentage removal of the metal ions and their distribution coefficient (K.sub.d) on GHBA resin was calculated using following formula

[K.sub.d] = Amount of metal ion in resin phase/Amount of metal ion in solution phase x Volume of solution (m1)/Weight of dry resin ml [g.sup.-1] i.e.

[K.sub.d] = [(I - F/F) X V/M](ml [g.sup.(-1)])

where I is the initial amount of the metal ion in solution, F is the final amount of metal ion after equilibrium with resin. V is the volume of metal ion solution (ml), and M is the weight of the resin taken (g).

Determination of Percentage Removal of Metal Ions Concentration

The initial metal ion concentration in solution and filtrate after equilibrium with resin were estimated using atomic absorption spectrophotometer. The percentage removal of metal ions was calculated using this formula.

Percentage removal of metal ions = [(I - F/I) X 100]

I = initial concentration of metal ions in solution, F = final amount of metal ions in solution after equilibrium with resin.

Determination of Ion Exchange Capacity

Resin capacity is usually expressed in terms of equivalents per liter (eq [1.sup.(-1)]) of resin or milli equivalents per dry gram of resin. The ion exchange capacity, which is generally taken as a measure of the hydrogen ion liberated by neutral salt to flow through the composite cation exchanger was determined by standard column process. 0.1 g (dry mass) of the composite ion exchange material in [H.sup.+] form was placed in a glass column with a glass wool support at the bottom. It was washed with demine-ralized water to remove any excess of acid remained on the particles. The hydrogen ions were eluted with 0.1 M solution of different alkali and alkaline earth salts. The flow rate was kept 4 ml [min.sup.(-1)]. The collected effluent was titrated against a standard solution of sodium hydroxide using phenolphthalein as an indicator. The hydrogen ions released were then calculated.

RESULTS AND DISCUSSION

FTIR Characterization of Guar Gum 4-Hydroxybenzoic Acid Resin

The FTIR spectrum of guar gum and synthesized GHBA resin was analyzed using KBr pellets. The FTIR spectrum of guar gum powder shows broad band in the region 3600-3200 [cm.sup.(-1)] characteristic of--OH stretching. The peak at 2945 [cm.sup.(-1)] is attributed to C--H stretching vibrations, strong and sharp peak at 1650 [cm.sup.(-1)] is due to 0--H bending, and variable peak at 1480-1350 [cm.sup.(-1)] is attributed to C--H bending. A strong peak at 1300-1000 [cm.sup.(-1)] denotes C-0 stretching vibration. The spectrum of guar gum is shown in Fig. 3.

The FTIR spectrum of GHBA resin peak at 2950 [cm.sup.(-1)] is attributed is to C--H stretching vibration. A strong peak in the region 1250-1000 [cm.sup.(-1)] denotes C-0 stretching vibrations. The peak at 1700-1680 [cm.sup.(-1)] is attributed to C=0 stretching vibrations of aryl carboxylic acid. The peaks at 1625-1450 [cm.sup.(-1)] are attributed to C=C stretching in aromatic nuclei. The GHBA resin in [H.sup.+] form in the symmetric stretching vibration region 2500-3000 [cm.sup.(-1)] is attributed to --OH group in carboxylic acid. The GHBA resin shows another variable peak at 1600-1500 [cm.sup.(-1)], which is attributed to C--H bending. The spectrum of polysaccharide generally observed in the region 3600-3200 [cm.sup.(-1)] is due to 0--H stretching frequency (35) The FTIR spectrum of GHBA resin is shown in Fig. 4.

Thermogravimetric Analysis

The resin sample was powdered to the same average mesh size and dried carefully in vacuum desiccators. The boat was packed uniformly for analysis. For the dynamic measurement, the system was heated at a constant heating rate of 20[degrees]C per minute under static air atmosphere till the complete decomposition. The degradation of GHBA resin occurred in two stages. The first stage, in the temperature range 340-425[degrees]C, had a weight loss of 74%. The second stage of decomposition from 400 to 600[degrees]C had a weight loss of 17% (36). The obtained thermogravimetric analysis (TGA) curve of GHBA resin is shown in Fig. 5.

Elemental Analysis

The percentage of elements in the synthesized resin was determined by elemental analyzer. Theoretically calculated percentage was 53.78 (C); 5.88 (H); and 40.34 (0). Found percentage was 53.32 (C); 5.22 (H); and 40.05 (0). The results of the elemental analysis are in good agreement with the calculated value.

Distribution Coefficient ([K.sub.d]) of Metal Ions in Effluent of Paradise Steel Industry, Jodhpur

The pH of experimental solution has a strong effect on the distribution coefficient ([K.sub.d]) of the metal ions. Table 2 shows the variation of [K.sub.d] values of different metal ions with ([H.sub.+]), which reveals the increase of the [K.sub.d] values with decreasing acidity of the aqueous solution and optimum results obtained at pH range 4-6. Metal sorption starts when the pH rises to the range where most acidic ion exchange sites start to exchange hydronium ion for metal and the capacity reaches the maximum value in the pH range where all the ion exchange sites take part in the reaction and the functional group is able to form complex with the metal cations (37).

TABLE 2. Distribution coefficient ([K.sub.d]) and percentage
removal of metal ions from effluent of Paradise Steel Industry,
Jodhpur on GHBA resin ([K.sub.d] x [10.sup.2]).

          [Fe.sup.2+]             [Zn.sup.2+]

pH  [ K.sub.d    Removal     [ K.sub.d    Removal     [ K.sub.d
      ] x [    percentage    ] x [    percentage    ] x [
    10.sup.2               10.sup.2               10.sup.2
        ]                      ]                      ]

1        9.86       48.63       8.56       46.11       6.52

2       27.86       73.59      20.67       67.40      13.27

3       71.52       87.73      66.76       86.97      31.13

4      178.23       94.68     162.97       93.02      65.41

5       78.88       88.75      99.40       90.85     121.63

6       25.86       72.11      15.92       61.42      46.56

7        8.60       46.25      12.71       44.64      14.05

 [Cu.sup.2+]         [Cd.sup.2+]             [Pb.sup.2+]

pH    Removal     [ K.sub.d    Removal     [ K.sub.d    Removal
    percentage    ] x [    percentage    ] x [    percentage
                10.sup.2               10.sup.2
                    ]                      ]

1        39.50       3.87       27.92       8.60       46.24

2        57.04       6.35       38.86      21.52       68.28

3        75.69      10.86       52.07      50.29       83.41

4        86.74      23.54       70.18      81.77       89.10

5        92.94      67.94       87.16      62.45       86.19

6        82.32     100.41       90.94      31.09       75.66

7        58.42      26.30       72.45      10.49       51.21


Removal of Metal Ions From Effluent of Paradise Steel Industry. Jodhpur by GHBA Resin

The results of percentage removal of metal ions from effluent of Paradise Steel Industry, Jodhpur by GHBA resin are summarized in Table 2. The adsorption percentage of the metal ions on the GHBA resin increases with pH and reaches its maximum value at pH 4-6 and then decline at higher pH. It has been found that the maximum removal percentage of Fe(II), Zn(II), Cu(II), Cd(II), and Pb(II) are 94.68%, 93.02%, 92.94%, 90.94%, and 89.10% respectively. The relative standard deviation (RSD) values of optimum removal percentage of metal ions are shown in Table 3. All data represent the mean of three independent experiments.

TABLE 3. Optimum results for the removal of metal ions from
the effluent of Paradise Steel Industry, Jodhpur on GHBA
resin.

                Amount        Amount
                of metal     loaded on
                ions in        GHBA        Removal
Metal ions   effluent (mg)   resin (mg)   percentage   RSD %

[Fe.sup.2+]       1.28         1.212        94.68       1.62

[Zn.sup.2+]       5.12         4.824        93.02       1.36

[Cu.sup.2+]      0.724         0.669        92.44       1.46

[Cd.sup.2+]      0.265         0.241        90.94       2.57

[Pb.sup.2+]      0.826         0.736        89.10       2.16


It is clear from the reported table that the percentage removal of metal ions first increases and then deceases with increasing pH. Similar results were obtained with previous study with amberlite IR-120 (38). It suggests that selectivity of metal ion is dependent on pH. The maximum removal of toxic metal ions have been obtained, when strong electric fields are present and electrostatic effect may become the dominant factor, such that small ions, which have a huge charge density are bound more strongly with resin (39). In acidic medium, the H+ ion of GHBA resin easily exchange with metal ions.

Ion Exchange Capacity

The ion exchange capacity was found to be 3.18 meq [g.sub.(-1)] of the dry GHBA resin.

Recovery of Metal Ions and Use of Eluent

The recoveries of adsorbed metal ions were determined in the column experiment. In the column experiment, the metal ions were eluted quantitatively with different strength of acids. The Pb(II) was eluted with 0.1 N HCI; Cd(II) with 0.5 N HCI; Cu(II) with 1.0 N HCI, Zn(II) with 1.5 N HC1, and Fe(II) was eluted with 2.0 N HCI. Then the resin column was washed thoroughly with de-mineralized water. The amounts of metal ions in the filtrate solution were analyzed by using AAS. Recovery of Pb(II), Cd(II), Cu(II), Zn(II), and Fe(II) were obtained 95.38%, 97.56%, 98.05%, 98.48%, and 99.09% respectively. The elution of metal ions were carried out with hydrochloric acid solution taken the advantage that chloride ion is an acceptable matrix for both AAS and spectrophotometric determination of metal ion. Data obtained in Table 4 indicate that different quantity and different strength of hydrochloric acid solution could afford quantitative elution of different metal ions from the resin. Dev and Rao have used modified Amberlite XAD-4 with bis-(N, N-salicylidene)-1,3-propanediamine for the separation of Ni(II), Fe(II), Ni(II), Co(II), Zn(II), Hg(II), Pb(II) and sorbed metals were eluted by 1 M HCI with a recovery of 98-100% (40).

TABLE 4. Quantitative separation of metal ions on GHBA column.

              Amount    Amount                         Eluent
              loaded    found    Recovery     Eluent   volume
Metal ion     (mg)      (mg)     percentage   use      (ml)

[Fe.sup.2+]   1.212     1.201      99.02     2.0 N HCI    60

[Zn.sup.2+]   4.824     4.751      98.48     1.5 N HCI    65

[Cu.sup.2+]   0.669     0.656      98.05     1.0 N HCI    60

[Cd.sup.2+]   0.241     0.234      97.56     0.5 N HCI    55

[pb.sup.2+]   0.736     0.702      95.38     0.1 N HCI    50


Column Reusability

To test the long-term stability of the column containing the GHBA resin, it was subjected to successive adsorption and desorption cycles by passing a metal ion solution through it at the optimum flow rate. The sorbed metal ion is then desorbed from the resin by appropriate eluent. The procedure was carried out several times. The stability of the column was assessed by monitoring the change in the recoveries of the sorbed metal ions. Results of 40 adsorption/desorption cycles in Table 5 indicated that the recovery decreased by 1-2% for metal ions, which reflect the good stability of the organic ligand on the resin.

TABLE 5. The recovery percentage of different metal ions on GHBA
resin (adsorption and desorption).

              Recovery percentage of different metal ions onto GHBA
                                 resin after cycles

Metal ions   1 cycle   10 cycles   20 cycles   30 cycles   40 cycles

[Fe.sup.2+]    94.68      91.83      89.57        89.51      89.50

[Zn.sup.2+]    93.02      90.16      88.04        87.98      87.96

[Cu.sup.2+]    92.44      89.76      87.96        97.53      87.88

[Cd.sup.2+]    90.94      87.63      85.84        85.79      85.78

[Pb.sup.2+]    89.10      86.23      84.45        84.40      84.38


Effect of Initial Metal Ion Concentration

The effect of metal ions concentration on the adsorption by the GHBA resin was investigated by varying the metal concentration from 0 to 150 mg [1.sup.(-1)] at a pH of 5.0 for 30 min equilibrium time (Fig. 6). It was observed that the adsorption percentage of metal ions was increased first with increasing the initial concentration of metal ion then reached a plateau value. It is obvious that for higher initial concentration, more efficient utilization of adsorption sites is expected due to a greater driving force by a higher concentration gradient. These high adsorption efficiencies were attributed to the hydrophilic nature of hydroxyl (--OH) and carboxylate ([COO.sup.-]) groups in GHBA resin, which had an adequate affinity to the metal ions. Similar results were obtained with previous study with chelating resin (41).

Effect of Stirring Time

To determine the rate of sorption of metal ions on the GHBA resin, batch experiments were elaborated by shaking the solution containing the ion with 100 mg of the GHBA resin at room temperature (25[degrees]C). Aliquots of 1.0 ml solution were taken out for analysis at pre-determined intervals. The concentration of metal ion in the supernatant solution was determined and the amount of metal ion sorbed on the GHBA resin was calculated by mass balance. The sorption halftime (612) defined as the time needed to reach 50% of the total sorption capacity was estimated from Fig. 7. From the data obtained, it was observed that the maximum sorption of metal ions with GHBA resin reached its equilibrium time after about 24 min. However, the time required for 50% sorption of metal ions was 11 mm for GHBA resin.

Effect of pH

The pH is an important parameter for adsorption of metal ions from aqueous solution because it affects the solubility of the metal ions, concentration of the counter ions on the functional groups of the adsorbent, and the degree of ionization of the adsorbent during reaction. To examine the adsorption percentage of metal ions with pH, the pH range was varied from 1.0 to 7.0 as given in Table 2. The uptake of free metal ions depends on pH, where optimum adsorption of metal ions occurs at different pH (4-6) and then declining at higher pH. Adsorption of metal ions on GHBA resin increased over pH range from 1.0 to 6.0, then decreases. At lower pH (acidic pH), the adsorbent surface will be completely covered with hydronium ions which compete strongly with metal ions for adsorption sites. With an increase in pH, the concentration of [H.sub.3][0.sup.+] ions decreases, facilitating the adsorption of metal ions by the adsorbent (42).

Effect of Agitation Speed

The effect of agitation speed on adsorption of metal ions was studied by varying the speed of agitation from 0 (without shaking) to 200 rpm, while keeping the optimum temperature (25[degrees]C) and optimum pH as constant. It is clear from Fig. 8 that the adsorption of metal ions on ion exchange resin generally increased with increasing agitation speed. The adsorption of metal ions on GHBA resin increased when agitation speed increased from 0 to 120 rpm. These results can be associated to the fact that the increase of the agitation speed improves the diffusion of metal ions toward the surface of the adsorbents. This also indicates that a shaking rate in the range 120-200 rpm is sufficient to assure that all the surface binding sites are made readily available for metal ions uptake. Then, the effect of external film diffusion on adsorption rate can be assumed not significant. For convenience, agitation speed of 130 rpm was selected as the optimum speed for GHBA resin for removal of metal ions from effluent of Paradise Steel Industry, Jodhpur. These results are in close agreement with that reported by Jeon and Park (43).

Effect of Treatment

Time Treatment time indicates that adsorption percentage of metal ions increased with an increase in contact time before equilibrium is reached. It is clear from Fig. 9 that adsorption of metal ions on GHBA resin increased when contact time was increased from 30 to 210 min, optimum contact time for GHBA adsorbent was found to be 210 min. Other parameters such as pH of solution and agitation speed were kept optimum, while temperature was kept at 25[degrees]C. Greater availability of carboxylic and ether functional groups on the surface of guar gum which are required for interaction with metal ions significantly improved the binding capacity and the process proceeded rapidly. This result is important, as equilibrium time is one of the important parameters for an economical wastewater treatment system.

Effect of Treatment Temperature

Figure 10 shows the effect of treatment temperature on the adsorption percentage of the metal ion on GHBA resin. The adsorption percentage of metal ions decreases by increasing the treatment temperature from 25[degrees]C to 50[degrees]C and then to 75[degrees]C at optimum treatment time of 4 hr. The working capacity of an ion exchanger depends on metal concentrations and temperatures. This observation is in full agreement with the published results by Khalil and Farag (44).

Effect of GHBA Dose on Adsorption of Metal Ions

The resin amount is also an important parameter to obtain the quantitative adsorption of metal ions. The quantitative adsorption is not obtained by smaller amount of resin than the optimum amount. The retention of the metal ions was examined in the relation to the amount of the resin. For this reason, amount of the resins were tested in the range of 20-200 mg and equilibrated for 4 hr. It is apparent that by increasing the resin amount, the adsorption density and the amount adsorbed metal ions per unit mass increases. The maximum adsorption by GHBA resin was achieved with an adsorbent dose of 100 mg and continued decreasing up to 200 mg. On increasing the GHBA resin concentration further, the binding of metal ions steadily decreased. This effect might be attributed to overlapping or aggregation of adsorption sites of resin resulting in a decrease in the total surface area of the adsorbent (45). The results are shown in Fig. 11.

Effect of Flow Rate

In the column experiment, the flow rate of the sample solution was an important parameter not only affecting the recovery of metal ions, but also controlling the time of analysis. Therefore, the effect of flow rate on adsorption of metal ions were investigated under the optimum conditions (pH, eluent, etc.) by passing 100 ml of sample solution through the micro column. The flow rates were adjusted in range of 1.0-5.0 ml [min.sup.(-1)] I controlled by a peristaltic pump. It was found that the optimum flow rate for these metal ions was 3-4 ml [min.sup.(-1)] for maximum loading and thereafter for stripping off from the chelating resin. Flow rates slower than 2 ml [min.sup.(-1)] were not studied to avoid long analysis times. However, at a flow rate greater than 4 ml [min.sup.(-1)], there was a decrease in the percentage of metal ion recovery, as the metal ions probably could not equilibrate properly with the resin bed. Thus, a flow rate of 4.0 ml [min.sup.(-1)] was selected throughout the column experiment.

CONCLUSIONS

The removal of [Fe.sup.2+], [Zn.sup.2+], [Cu.sup.2+], [Cd.sup.2+], and [Pb.sup.2+] ions by GHBA resin is now considered one of the most promising technique due to its cost-effectiveness, eco-friendliness, and rapidness. The optimum conditions for removal of [Fe.sup.2+], [Zn.sup.2+], [Cu.sup.2+], [Cd.sup.2+], and [Pb.sup.2+] ions using GHBA cation exchange resin were found to be pH 4-6 and stirring time ~25 min. The RSDs of the repeatability and the reproducibility are [Less Than Sing] 3.0%. These results indicate that the present method can be used for quantitative analyses and removal of toxic metal ions. Exchange bed could be used more than 40 cycles with little loss of exchange capacity. A concentration of 0.1-2.00 N HC1 as eluent was sufficient to obtain maximum recovery for all metal ions from the obtained results. The selectivity and ion-exchange capacity of these materials toward metals ions can be controlled by pH of the medium, contact time, temperature, adsorbent dose, agitation speed, etc. Therefore, the GHBA resin is applicable for the removal and recovery of heavy metal ions from industrial effluents.

ACKNOWLEDGMENTS

The authors are thankful to the Head, Department of Chemistry, J.N.V. University, Jodhpur, for providing all necessary facilities.

Correspondence to: A.V. Singh; e-mail: areshvikram04@rediffmail.com

DOI 10.1002/pen.23294

Published online in Wiley Online Library (wileyonlinelibrary.com).

[c] 2012 Society of Plastics Engineers

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A.V. Singh, indraj Kumar Kumawat

Department of Chemistry, Jai Narain Vyas University, Jodhpur 342033, Rajasthan, India
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Author:Singh, A.V.; Kumawat, Indraj Kumar
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