**6. Experimental**

Ion exchange is a very versatile and effective tool for treatment of aqueous hazardous wastes. The role of ion exchange in dye effluents treatment is to reduce the magnitude of hazardous load by converting them into a form in which they can be reused, leaving behind less toxic substances in their places or to facilitate ultimate disposal by reducing the hydraulic flow of the stream bearing toxic substances. Another significant feature of the ion exchange process is

Ion exchange resins known as reactive polymers are highly ionic, covalently cross-linked, insoluble polyelectrolytes, usually supplied as beads. Ion exchange resins have been classified based on the charge of the exchangeable counter-ion (cation exchanger or anion exchanger) and the ionic strength of the bound ion (strong exchanger or weak exchanger). Thus, there are four primary types of ion exchange resins: (a) strong cation exchange resins, containing —

secondary (=NH) or tertiary-amine (≡N) functional groups in the chloride or hydroxide form.

The resin beads have either a dense internal structure with no discrete pores (gel resins, also called microporous) or a porous, multichannelled structure (macroporous or macroreticular resins). They are commonly prepared from styrene and various levels of the cross-linking agent – divinylbenzene, which controls the particles' porosity. Popular ion exchangers available on the market are those of acrylic, epoxy-amine and phenol-formaldehyde matrices. The common choice is between styrene-divinylbenzene or acrylic-divinylbenzene copolymer. Disregarding structural features (gel or macroporous) for the time being, the acrylic matrix is more elastic than the rigid styrene-based copolymer. However, the elastic resilience of acrylic matrix could

be of concern where the columns of resin operate under a high net compression force.

The internal structure of the resin beads, i.e. whether microporous (gel-type) or macropo‐ rous, is important in the selection of an ion exchanger. Macroporous resins, with their high effective surface area, facilitate the ion exchange process. They also give access to the exchange sites for larger ions, can be used with almost any solvent, irrespective of whether it is a good one forthe uncross-linked polymer, and take up the solvent with little or no change in volume. They make more rigid beads, facilitating the ease of removal from the reaction system. In the case of the microporous resins, since they have no discrete pores, solute ions diffuse through the particle to interact with the exchange sites. Despite diffusion limitations on the reaction rates, these resins offer certain advantages: they are less fragile, requiring less care in handling, react faster in functionalization and application reactions as well as possess higher

Taking into account high capacity and selectivity of ion exchange resins for different dyes, they seem to be proper materials for dyes sorption from textile effluents. Applicability of the anion exchange resins in the removal of acid, reactive, direct dyes widely used in the textile industry, from aqueous solutions and wastewaters, was confirmed in some papers [2, 15, 20, 23, 25–28].

groups or the corresponding salts, (b) weak cation exchange resins, containing —

groups or the corresponding salts, (c) strong anion exchange resins of quaternary

+

groups), (d) weak anion exchange resins of primary (-NH2),

Cl– groups and type II resins contain

that it has the ability to separate as well as to concentrate pollutants.

ammonium groups (type I resins contain —CH2N(CH3)3

Cl–

SO3 - H+

COO-H+

—CH2N(CH3)2(CH2CH2OH)+

46 Ion Exchange - Studies and Applications

loading capacities [25].

In the paper, the results of the sorption of three textile dyes such as C.I. Acid Orange 7, C.I. Reactive Black 5 and C.I. Direct Blue 71 on the commercially available anion exchangers are summarized and discussed based on the data presented in papers [2, 15, 20, 23, 25–31].

The essential physicochemical properties of these resins (produced by Lanxess, Germany or Dow Chemical Company, USA) are given in Table 6 and Figure 4. The resins were washed with both 1 M HCl and distilled water in order to remove impurities and change the ionic form to the chloride one. The resins were dried at room temperature to the constant mass.

Molecular structures of the above mentioned dyes are presented in Figure 5. The dyes were purchased from Sigma-Aldrich (Germany) and used without further purification. These dyes were selected for the studies because they are extensively used in the textile industry. C.I. Acid Orange 7 is applied for fibers such as silk, wool and nylon using neutral to acid dye baths. Direct Blue 71 is used for cotton, paper, leather, wool, silk and nylon dyeing. Reactive dyes, e.g. RB5, are by far the best choice for dyeing of cotton and other cellulose fibers.


The other chemicals used were produced by Sigma-Aldrich (Germany) and were of analytical grade.

where: - weakly basic anion exchangers, - intermediate base anion exchangers, - strongly basic anion exchangers, S-DVB – styrene-divinylbenzene, A-DVB – acrylic-divinylbenzene, PF- phenol-formaldehyde, m – macro‐ porous, g - gel

**Table 6.** Properties of applied anion exchangers

macroporous, e) gel

Lewatit MonoPlus

Lewatit MonoPlus

Lewatit MonoPlus

M 500

M 600

MP 500 — N+

Amberlite IRA 910 — N+

(CH3)3

Table 6. Properties of applied anion exchangers

Amberlite IRA 458 A-DVB, g 1.25 35 0.6–0.9 Amberlite IRA 958 A-DVB, g >0.8 80 0.63–0.85

where: - weakly basic anion exchangers, - intermediate base anion exchangers, -

**Figure 4.** Composition of resin matrices: a) styrene-divinylbenzene skeleton, b) acrylic-divinylbenzene skeleton, c) phe‐ nol-formaldehyde skeleton, and their structure: d) macroporous, e) gel

The sorption studies were performed by the batch method. The dye solutions (50 mL) were shaken with the dry anion exchanger (0.5 g) in conical flasks using a thermostated laboratory shaker Elphin (Poland) at 20<sup>ο</sup> C. The experiments were conducted in the two parallel series with the reproducibility 5%. The amount of dye adsorbed after time *t*, *qt* (mg/g), was calculated from Equation 1:

Figure 4. Composition of resin matrices: a) styrene-divinylbenzene skeleton, b) acrylic-

$$q\_t = \frac{(\mathbf{C}\_0 - \mathbf{C}\_t)}{w} \times V \tag{1}$$

S-DVB, m >1.1 45 0.63

S-DVB, g 1.1 70 0.64

S-DVB, g 1.3 30 0.62

(CH3)2C2H4OH S-DVB, m 1.1 60 0.53–0.8

where: *C0* and *Ct* (mg/L) are the liquid-phase concentrations of dye at the time *t=0* and after time *t*, respectively, *V* (L) is the volume of solution and *w* (g) is the mass of dry anion exchanger.

C.I. Acid Orange 7; C.I. No 15510; MW = 350.32 g/mol

To test the influence of shaking speed on dye removal, preliminary experiments were carried out by varying the shaking speed from 140 to 200 rpm. The best results were obtained for the shaking speed 180 rpm. Therefore, 180 rpm was used in all batch experiments. To evaluate the kinetics of the sorption process, 50 mL solutions of 100 mg/L (or 500 mg/L or 1000 mg/L) dye concentration and 0.5 g of the anion exchanger samples were used. The shaking time was varied from 1 to 12 h, respectively (e.g. up to equilibrium). All the kinetic studies were carried out at the natural pHs (pH 4.98–5.83) of solutions (pH-meter; CX-742 Elmetron, Poland). The dyes concentration after the sorption was measured spectrophotometrically at the maximum absorbance wavelengths. Absorption spectra of raw textile wastewaters of different compo‐ sition were recorded for the predetermined time interval of decolourization using a spectro‐ photometer Specord M-42 (Carl Zeiss, Germany).

Anion Exchange Resins as Effective Sorbents for Removal of Acid, Reactive, and Direct Dyes from Textile Wastewaters http://dx.doi.org/10.5772/60952 49

> C.I. Acid Orange 7; C.I. No 15510; MW = 350.32 g/mol sodium salt of 4‐(2‐hydroxynaphthylazo)benzenesulfonic acid

C.I. Reactive Black 5; C.I. No 20505; MW = 991.82 g/mol tetrasodium salt of 4‐amino‐5‐hydroxy‐3,6‐bis((4‐((2‐(sulfooxy) ethyl)sulfonyl)phenyl)azo)‐2,7‐ naphthalenedisulfonic acid

C.I. Direct Blue 71; C.I. No 34140; MW = 1029.88 g/mol tetrasodium 3‐[(E)‐{4‐[(E)‐{4‐[2‐(6‐amino‐1‐oxo‐3‐sulfonatonaphthalen‐2(1H) ylidene)hydrazino]‐6‐ sulfonatonaphthalen‐1‐yl}diazenyl]naphthalen‐1‐yl}diazenyl]naphthalene‐1,5‐disulfonate

Figure 5. Dyes characteristics **Figure 5.** Dyes characteristics

Lewatit MonoPlus

Lewatit MonoPlus

Lewatit MonoPlus

48 Ion Exchange - Studies and Applications

M 500

M 600

macroporous, e) gel

from Equation 1:

where: *C0* and *Ct*

shaker Elphin (Poland) at 20<sup>ο</sup>

MP 500 — N+

Amberlite IRA 910 — N+

phenol-formaldehyde, m – macroporous, g - gel

CH2 CH CH2 CH CH2 CH

CH2 CH CH2 CH CH2

CH2

nol-formaldehyde skeleton, and their structure: d) macroporous, e) gel

photometer Specord M-42 (Carl Zeiss, Germany).

Table 6. Properties of applied anion exchangers

(CH3)3

Amberlite IRA 458 A-DVB, g 1.25 35 0.6–0.9 Amberlite IRA 958 A-DVB, g >0.8 80 0.63–0.85

where: - weakly basic anion exchangers, - intermediate base anion exchangers, strongly basic anion exchangers, S-DVB – styrene-divinylbenzene, A-DVB – acrylic-divinylbenzene, PF-

> CH2 CH COOCH3 <sup>n</sup>

> > CH2 CH COOCH3 <sup>n</sup>

CH2 CH

CH CH2

CH CH2

 **a) b) c)** 

CH2 CH

Figure 4. Composition of resin matrices: a) styrene-divinylbenzene skeleton, b) acrylicdivinylbenzene skeleton, c) phenol-formaldehyde skeleton, and their structure: d)

C. The experiments were conducted in the two parallel series

 **d) e)**

**Figure 4.** Composition of resin matrices: a) styrene-divinylbenzene skeleton, b) acrylic-divinylbenzene skeleton, c) phe‐

The sorption studies were performed by the batch method. The dye solutions (50 mL) were shaken with the dry anion exchanger (0.5 g) in conical flasks using a thermostated laboratory

with the reproducibility 5%. The amount of dye adsorbed after time *t*, *qt* (mg/g), was calculated

<sup>0</sup> ( ) - = ´ *<sup>t</sup>*

*C C q V w*

*t*

C.I. Acid Orange 7; C.I. No 15510; MW = 350.32 g/mol

time *t*, respectively, *V* (L) is the volume of solution and *w* (g) is the mass of dry anion exchanger.

To test the influence of shaking speed on dye removal, preliminary experiments were carried out by varying the shaking speed from 140 to 200 rpm. The best results were obtained for the shaking speed 180 rpm. Therefore, 180 rpm was used in all batch experiments. To evaluate the kinetics of the sorption process, 50 mL solutions of 100 mg/L (or 500 mg/L or 1000 mg/L) dye concentration and 0.5 g of the anion exchanger samples were used. The shaking time was varied from 1 to 12 h, respectively (e.g. up to equilibrium). All the kinetic studies were carried out at the natural pHs (pH 4.98–5.83) of solutions (pH-meter; CX-742 Elmetron, Poland). The dyes concentration after the sorption was measured spectrophotometrically at the maximum absorbance wavelengths. Absorption spectra of raw textile wastewaters of different compo‐ sition were recorded for the predetermined time interval of decolourization using a spectro‐

(mg/L) are the liquid-phase concentrations of dye at the time *t=0* and after

S-DVB, m >1.1 45 0.63

S-DVB, g 1.1 70 0.64

S-DVB, g 1.3 30 0.62

H2C HO CH

H2C HO CH

CH2

CH2

HO C H O

<sup>n</sup> <sup>n</sup>

(1)

<sup>n</sup> <sup>n</sup>

N OH HO C H O

N OH

(CH3)2C2H4OH S-DVB, m 1.1 60 0.53–0.8

Sorption isotherm studies were carried out analogously using dyes solutions of the increasing initial concentration at 20<sup>ο</sup> C for 24 h. The effects of salts and surfactant additions on dyes' uptake at equilibrium were studied by shaking the anion exchanger (0.5 g) with the 100 mg/L dye solution containing different amounts of salts (Na2SO4, Na2CO3, NaCl) or surfactants The sorption studies were performed by the batch method. The dye solutions (50 mL) were shaken with the dry anion exchanger (0.5 g) in conical flasks using a thermostated laboratory shaker Elphin (Poland) at 20 C. The experiments were conducted in the two (sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB)). The dyes concentration after the sorption was measured spectrophotometrically at the maximum absorbance wavelengths depending on the system.

Regeneration tests for the anion exchange resin were conducted with different regeneration agents (1 M HCl, 1 M NaOH, 1 M KSCN, 1 M NaCl, 1 M Na2SO4, 1 M Na2CO3, 90% methanol, 1 M KSCN or 1 M NaOH or 1 M HCl in 90% methanol). The loaded resin containing 10 mg/g of dye was put into flasks in contact with 50 mL of different eluting agents. The flasks were agitated for 3 h and the dye concentrations in the solution were determined at the maximum absorbance wavelength in order to calculate the desorption percentage (%).

The above methods were described in detail in [2, 15, 20, 23, 25–31].
