**7. Results and discussion**

#### **7.1. Adsorption equilibrium and retention mechanisms**

The equilibrium sorption isotherms are one of the most important data to understand the mechanism of the sorption. They describe the ratio between the quantity of sorbate retained by the sorbent and that remaining in the solution at the constant temperature at equilibrium and are important from both theoretical and practical points of view. The parameters obtained from the isotherm models provide important information not only about the sorption mech‐ anisms but also about the surface properties and affinities of the sorbent. The best known adsorption models in the linearized form for the single-solute systems are:

**a.** the Langmuir isotherm

$$\frac{C\_e}{q\_e} = \frac{1}{Q\_0 b} + \frac{C\_e}{Q\_0} \tag{2}$$

where *Q0* (mg/g) is the Langmuir monolayer sorption capacity, *b* (L/mg) is the Langmuir adsorption constant, calculated from the intercepts and slopes of straight lines of plot of *Ce /qe* vs *Ce*.

The Langmuir isotherm is applied to homogeneous adsorption based on the following assumptions: (a) all the adsorption sites are identical; (b) each site retains one molecule of the given compound; (c) all sites are energetical and sterical independent of the adsorbed quantity [32].

**b.** the Freundlich isotherm

$$
\log q\_{\varepsilon} = \log k\_{\mathbb{F}} + \frac{1}{n} \log \mathbb{C}\_{\varepsilon} \tag{3}
$$

where: *kF* (mg/g) is the Freundlich adsorption capacity, *n* is the Freundlich constant related to the surface heterogeneity, determined from the slope and intercept of the linear plot of *log q*<sup>e</sup> vs *log Ce*.

(sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB)). The dyes concentration after the sorption was measured spectrophotometrically at the maximum

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

The equilibrium sorption isotherms are one of the most important data to understand the mechanism of the sorption. They describe the ratio between the quantity of sorbate retained by the sorbent and that remaining in the solution at the constant temperature at equilibrium and are important from both theoretical and practical points of view. The parameters obtained from the isotherm models provide important information not only about the sorption mech‐ anisms but also about the surface properties and affinities of the sorbent. The best known

0 0

where *Q0* (mg/g) is the Langmuir monolayer sorption capacity, *b* (L/mg) is the Langmuir adsorption constant, calculated from the intercepts and slopes of straight lines of plot of *Ce /qe*

The Langmuir isotherm is applied to homogeneous adsorption based on the following assumptions: (a) all the adsorption sites are identical; (b) each site retains one molecule of the given compound; (c) all sites are energetical and sterical independent of the adsorbed quantity

<sup>1</sup> log log log = + *eF e qk C*

*n*

*q Qb Q* (2)

(3)

1 = + *e e*

*C C*

absorbance wavelength in order to calculate the desorption percentage (%).

adsorption models in the linearized form for the single-solute systems are:

*e*

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

**7.1. Adsorption equilibrium and retention mechanisms**

absorbance wavelengths depending on the system.

**7. Results and discussion**

50 Ion Exchange - Studies and Applications

**a.** the Langmuir isotherm

**b.** the Freundlich isotherm

vs *Ce*.

[32].

The Freundlich isotherm assumes heterogeneous surface with a non-uniform distribution of heat of adsorption [33].

The applicability of isotherm equations was compared in this paper by judging the determi‐ nation coefficients (*R2* ). The calculated constants of these models were largely dependent on the type of the anion exchanger (Tables 7–9). Not only the basicity of the resin but also the matrix composition and structure were the determining factors of sorption. It could be stated generally that the Langmuir isotherm model fits better than the Freundlich one. However, the comparison of the *R2* values indicates that the experimental data of C.I. Direct Blue 71 adsorp‐ tion onto Amberlite IRA 67, Amberlite IRA 900 and Lewatit MonoPlus MP 62 were more appropriate for the Freundlich isotherm model. It could be in agreement with the aggregation tendency of the C.I. Direct Blue 71 dye, especially at high concentrations, and with the possibility of the dye uptake through many types of interactions. Similar observations were described for C.I. Basic Blue 9 sorption onto Purolite C 145 and Purolite C 107E resins by Suteu et al. [34].


**Table 7.** Comparison of the isotherms parameters for C.I. Acid Orange 7 sorption on the studied anion exchangers


**Table 8.** Comparison of the isotherms parameters for C.I. Reactive Black 5 sorption on the studied anion exchangers


Anion Exchange Resins as Effective Sorbents for Removal of Acid, Reactive, and Direct Dyes from Textile Wastewaters http://dx.doi.org/10.5772/60952 53


**Table 9.** Comparison of the isotherms parameters for C.I. Direct Blue 71 sorption on the studied anion exchangers

Based on the values of the monolayer sorption capacities determined from the Langmuir isotherm model, the studied anion exchangers can be arranged in the following sorption effectiveness series as:

**•** for C.I. Acid Orange 7

**Anion exchanger**

52 Ion Exchange - Studies and Applications

Amberlite IRA 478RF

Amberlite IRA 900

MP 500

M 500

M 600

Lewatit MonoPlus

Lewatit MonoPlus

Lewatit MonoPlus

**Anion exchanger**

Amberlite IRA 478RF

Amberlite IRA 900

MP 500

M 500

Lewatit MonoPlus

Lewatit MonoPlus

**Langmuir isotherm model Freundlich isotherm model**

*Q0 (mg/g) b (L/g) R2 kF n R2*

150.4 0.057 0.999 93.0 16.1 0.906 [25]

1351.8 0.039 0.999 179.4 6.92 0.845 [31]

1170.5 0.416 0.996 312.1 3.24 0.955 This study

17.4 0.099 0.998 3.83 3.69 0.789 This study

4.6 0.236 0.896 0.15 1.2 0.629 This study

Lewatit MonoPlus MP 62 796.1 0.049 0.990 183.5 4.96 0.925 [23] Amberlyst A 23 282.1 0.204 0.999 125.6 8.77 0.937 [23] Amberlite IRA 67 66.4 0.503 0.998 26.4 7.10 0.914 [23]

Amberlite IRA 458 1329.5 0.037 0.999 241.3 4.92 0.823 [30] Amberlite IRA 958 1655.2 0.468 0.999 263.2 3.21 0.815 [30] Amberlite IRA 910 1219.9 0.021 0.998 172.4 4.62 0.794 [30]

**Table 8.** Comparison of the isotherms parameters for C.I. Reactive Black 5 sorption on the studied anion exchangers

Lewatit MonoPlus MP 62 470.6 0.0003 0.874 1.47 0.86 0.931 [20]

Amberlite IRA 67 90.9 0.005 0.909 1.02 1.57 0.998 [20] Lewatit MonoPlus MP 64 420.4 0.021 0.997 24.2 2.35 0.510 [20]

Amberlyst A 23 456.2 0.079 0.994 22.2 2.69 0.645 This study

**Langmuir isotherm model Freundlich isotherm model**

*Q0 (mg/g) b (L/g) R2 kF n R2*

41.8 0.0047 0.974 4.67 3.6 0.969 [25]

778.2 0.0001 0.828 0.21 1.18 0.901 [20]

523.6 0.0023 0.959 2.65 1.39 0.874 [20]

2.02 0.165 0.692 0.14 1.06 0.509 [20]

Lewatit MonoPlus MP 64 592.7 0.242 0.999 84.3 3.45 0.717 This study

**Ref.**

**Ref.**

Amberlite IRA 958 > Amberlite IRA 900 > Amberlite IRA 478RF > Amberlite IRA 458 > Amberlite IRA 910 > Lewatit MonoPlus MP 500 > Lewatit MonoPlus MP 64 > Lewatit MonoPlus M 500 > Lewatit MonoPlus M 600 > Amberlite IRA 67 > Amberlyst A 23 ≈ Lewatit MonoPlus MP 62

**•** for C.I. Reactive Black 5

Amberlite IRA 958 > Amberlite IRA 458 > Amberlite IRA 900 > Amberlite IRA 910 > Lewatit MonoPlus MP 500 > Lewatit MonoPlus MP 62 > Lewatit MonoPlus MP 64 > Amberlyst A 23 > Amberlite IRA 478RF > Amberlite IRA 67 > Lewatit MonoPlus M 500 > Lewatit MonoPlus M 600

**•** for C.I. Direct Blue 71

Amberlite IRA 958 > Amberlite IRA 900 > Amberlite IRA 910 > Lewatit MonoPlus MP 500 > Lewatit MonoPlus MP 62 > Amberlyst A 23 > Lewatit MonoPlus MP 64 > Amberlite IRA 67 > Amberlite IRA 458 > Amberlite IRA 478RF > Lewatit MonoPlus M 500 ≈ Lewatit MonoPlus M 600 + *I* − ˉ + *I* − ˉ + *I* ˉ− + *R*1( ) ˉ + *I* ˉ− + *R*1( ) ˉ

as far as their applicability is concerned in removal of these dyes.

Under experimental conditions, sorption of the dyes occurred between the sulphonic groups of dyes (e.g. R1(SO3 - )4(Na+ )4) and the functional groups of the weakly (*RCH*2*NH* (*CH*3) <sup>2</sup> *C* ) or strongly (*RCH*2*N* (*CH*3) <sup>3</sup> *C* ) basic anion exchangers in the chloride form [25]:

$$\begin{aligned} \text{4RCH}\_{2}\text{NH}(\text{CH}\_{3}\text{)}\_{2}\text{"}\text{CI}^{-}+\text{R}\_{1}\text{(}\underset{\text{SO}\_{3}^{\text{-}}}{\text{O}}\_{\text{Na}^{\text{+}}}\text{(}\text{}\_{\text{Na}^{\text{+}}}\text{)} & \rightleftharpoons \text{[RCH}\_{2}\text{NH}(\text{CH}\_{3}\text{)}\_{2}\text{I}\_{4}\text{(}\text{SO}\_{3}^{\text{-}}\text{)}\_{4}\text{R}\_{1} + 4\text{NaCl} \\ \text{4RCH}\_{2}\text{N(CH}\_{3}\text{)}\_{3}\text{'}\text{CI}^{-}+\text{R}\_{1}\text{(}\_{\text{SO}\_{3}^{\text{-}}}\text{(}\_{\text{Na}^{\text{+}}}\text{)} & \rightleftharpoons \text{[RCH}\_{2}\text{N(CH}\_{3}\text{)}\_{3}\text{I}\_{4}\text{(}\text{SO}\_{3}^{\text{-}}\text{)}\_{4}\text{R}\_{1} + 4\text{NaCl} \end{aligned}$$

The dye anions (R1(SO3 - )4) replaced exchangeable chloride anions which compensates posi‐ tive electric charge of the tertiary amine or quaternary ammonium groups of the anion exchanger. The ion pairs are formed between these groups. Such interactions were revealed during the analysis of the ATR FT-IR spectra of the dye loaded anion exchangers, the absorp‐ tion peaks at 1170–1047 nm and 1019 nm were attributed to the presence of –SO3 – and –S=O groups [20]. In the FT-IR spectrum of the weakly basic anion exchanger Purolite A 847 with loaded azo- (Lanasyn Navy M-DNL) and phthalocyanine (C.I. Acid Blue 249) dyes, the vibrations at 1042 nm and 1032 nm related to –SO3 – groups were detected by Kaušpėdienė et al. [35].Althoughionexchange is a significantmechanismindyes sorption, some extentofphysical adsorption can also occur. The attachment through hydrophobic π–π interactions between the aromatic rings of the dye and the matrix of the anion exchanger ('like attracts like') is consid‐ ered. These interactions play a more extensive role in the case of the polyacrylic resins like Amberlite IRA 958, IRA 458 or IRA 67 compared to those of polystyrene-based materials. High affinity of dyes for the anion exchangers can also result from the formation of H-bondings, which can be created between nitrogen of the quaternary ammonium groups of strongly basic anionexchange resins andnitrogenofthe―NH2groupofdyes aswell asoxygenofthe carbonyl group of the resins and the ―NH2 group of dye. Also oxygen atom of the carbonyl group of anion exchangers and oxygen atom of the hydroxyl group or nitrogen atom of the azo group of dyes through the water molecules could interact. Possible interactions between the anions of C.I. Reactive Black 5 and the strongly basic anion exchangers of polyacrylic matrices are shown inFigure 6.Kaušpėdienė et al.[35,36] alsoobservedthatmore thanone interactionwas involved in dyes sorption on Purolite A 847 of polyacrylic matrix: ion exchange and nonelectrostatic interactions. The studies on the sorption of dyes and organic compounds on the ion exchang‐ ers reported so far showed that the size of the sorbate molecules has a considerable effect on the sorption degree. Organic dye molecules of different positions of sulfonic groups as well as the number of other anionic groups and their charges can interact in a different way with anion exchangers. Of significant importance in the removal of dye anions by an anion exchanger is the resin structure. Concerning the exchange of large molecular weight species like dyes, the macroporous property becomes important in providing an easier diffusion path for uptake compared with the gel structure. Amberlite IRA 958 as the anion exchanger with the macropo‐ rous structure possesses significant porosity in comparison with that of gel Amberlite IRA 458 or IRA 67. Therefore, sorption capacity of Amberlite IRA958 is much more bigger than that of Amberlite IRA 458 of the same functional groups in the case of C.I. Direct Blue 71 sorption. Taking into consideration the strongly basic anion exchangers Lewatit MonoPlus M 500 and LewatitMonoPlusM600ofpolystyrenematrixandgelstructure,averylowcapacityisobserved. Additionally, flat structure of the reactive and direct dyes can inhibit the interactions be‐ tween the dyes and the anion exchangers. Also when the dye anions are too large, they are excluded because of resin structure ('sieve effect'). Besides, because large size dyes have the tendency to form aggregates in the solution rather than in the resin phase [25].

#### **7.2. Influence of auxiliaries such as salts and surfactants**

Auxiliaries such as inorganic electrolytes and surfactants are widely used in chemical treat‐ ment of fibers. They remain in wastewaters at a concentration close to the initial one. Depend‐ ing on the class of dye, dyeing process requires application of other auxiliaries. Acid dyes are the most numerous group of those known. They occur in the form of sodium salts of colured compounds containing 1–3 sulfonic or carboxylic groups. They belong to strong electrolytes, undergo complete dissociation in water into coloured anions. The condition of their binding with fibre is forming a sufficient number of the ammonium groups in wool which can be obtained by the addition of acids to dyeing baths, hence it is said 'they dye in the acid bath'. Disposal of the carboxylic acids to the textile sewages in Europe amounts from 15, 000 to 20, 000 tons/year [16]. The condition of their binding with fibre is forming a sufficient number of the ammonium

The dye anions (R1(SO3

54 Ion Exchange - Studies and Applications


vibrations at 1042 nm and 1032 nm related to –SO3

)4) replaced exchangeable chloride anions which compensates posi‐

–

groups were detected by Kaušpėdienė et al.

and –S=O

tive electric charge of the tertiary amine or quaternary ammonium groups of the anion exchanger. The ion pairs are formed between these groups. Such interactions were revealed during the analysis of the ATR FT-IR spectra of the dye loaded anion exchangers, the absorp‐

groups [20]. In the FT-IR spectrum of the weakly basic anion exchanger Purolite A 847 with loaded azo- (Lanasyn Navy M-DNL) and phthalocyanine (C.I. Acid Blue 249) dyes, the

[35].Althoughionexchange is a significantmechanismindyes sorption, some extentofphysical adsorption can also occur. The attachment through hydrophobic π–π interactions between the aromatic rings of the dye and the matrix of the anion exchanger ('like attracts like') is consid‐ ered. These interactions play a more extensive role in the case of the polyacrylic resins like Amberlite IRA 958, IRA 458 or IRA 67 compared to those of polystyrene-based materials. High affinity of dyes for the anion exchangers can also result from the formation of H-bondings, which can be created between nitrogen of the quaternary ammonium groups of strongly basic anionexchange resins andnitrogenofthe―NH2groupofdyes aswell asoxygenofthe carbonyl group of the resins and the ―NH2 group of dye. Also oxygen atom of the carbonyl group of anion exchangers and oxygen atom of the hydroxyl group or nitrogen atom of the azo group of dyes through the water molecules could interact. Possible interactions between the anions of C.I. Reactive Black 5 and the strongly basic anion exchangers of polyacrylic matrices are shown inFigure 6.Kaušpėdienė et al.[35,36] alsoobservedthatmore thanone interactionwas involved in dyes sorption on Purolite A 847 of polyacrylic matrix: ion exchange and nonelectrostatic interactions. The studies on the sorption of dyes and organic compounds on the ion exchang‐ ers reported so far showed that the size of the sorbate molecules has a considerable effect on the sorption degree. Organic dye molecules of different positions of sulfonic groups as well as the number of other anionic groups and their charges can interact in a different way with anion exchangers. Of significant importance in the removal of dye anions by an anion exchanger is the resin structure. Concerning the exchange of large molecular weight species like dyes, the macroporous property becomes important in providing an easier diffusion path for uptake compared with the gel structure. Amberlite IRA 958 as the anion exchanger with the macropo‐ rous structure possesses significant porosity in comparison with that of gel Amberlite IRA 458 or IRA 67. Therefore, sorption capacity of Amberlite IRA958 is much more bigger than that of Amberlite IRA 458 of the same functional groups in the case of C.I. Direct Blue 71 sorption. Taking into consideration the strongly basic anion exchangers Lewatit MonoPlus M 500 and LewatitMonoPlusM600ofpolystyrenematrixandgelstructure,averylowcapacityisobserved. Additionally, flat structure of the reactive and direct dyes can inhibit the interactions be‐ tween the dyes and the anion exchangers. Also when the dye anions are too large, they are excluded because of resin structure ('sieve effect'). Besides, because large size dyes have the

–

tion peaks at 1170–1047 nm and 1019 nm were attributed to the presence of –SO3

tendency to form aggregates in the solution rather than in the resin phase [25].

Auxiliaries such as inorganic electrolytes and surfactants are widely used in chemical treat‐ ment of fibers. They remain in wastewaters at a concentration close to the initial one. Depend‐

**7.2. Influence of auxiliaries such as salts and surfactants**

Acid dyes are divided into three groups differing in dyeing conditions. The first group includes so-called well equalizing dyes that is providing uniform level dyeing of a relatively small molecular mass. They are used for dyeing in acid bath of pH 2–2.5 with the addition of strong acids, e.g. H2SO4. groups in wool which can be obtained by the addition of acids to dyeing baths, hence it is said 'they dye in the acid bath'. Disposal of the carboxylic acids to the textile sewages in Europe amounts from 15,000 to 20,000 tons/year [16]. Acid dyes are divided into three groups differing in dyeing conditions. The first group includes so-called well equalizing dyes that is providing uniform level dyeing of a

relatively small molecular mass. They are used for dyeing in acid bath of pH 2–2.5 with the

addition of strong acids, e.g. H2SO4.

Figure 6. Mechanism of interactions between C.I. Reactive Black 5 and strongly basic anion exchanger of the polyacrylic matrix **Figure 6.** Mechanism of interactions between C.I. Reactive Black 5 and strongly basic anion exchanger of the polyacryl‐ ic matrix

The second group includes dyes of more developed molecules and greater affinity for wool. They are used for dyeing in the baths of pH 4.5–5 acidified with acetic acid. The third group has badly equalizing dyes of largely expended molecules and great affinity for wool. They are applied for dyeing in the baths of pH 5.5–6.5 in the presence of ammonium salts (sulfate, acetate), which decompose only at increased temperature acidifying the bath. Usually, sodium sulfate is added to the dyeing bath in the amount 10–20% in the proportion

to the fibre and 1–2% of formic, acetic or sulfuric acid.

The second group includes dyes of more developed molecules and greater affinity for wool. They are used for dyeing in the baths of pH 4.5–5 acidified with acetic acid. The third group has badly equalizing dyes of largely expended molecules and great affinity for wool. They are applied for dyeing in the baths of pH 5.5–6.5 in the presence of ammonium salts (sulfate, acetate), which decompose only at increased temperature acidifying the bath. Usually, sodium sulfate is added to the dyeing bath in the amount 10–20% in the proportion to the fibre and 1– 2% of formic, acetic or sulfuric acid.

The influence of inorganic salts such as NaCl and Na2SO4 on the sorption of C.I. Acid Orange 7 from the solution of the initial concentration 100 mg/L was studied. The results indicate that the presence of these salts in the whole examination concentration of 1–25 g/L does not affect the dye adsorption significantly. In the case of the increasing amount of sodium sulfate in the solution from 1 to 25 g/L, the anion exchange capacities of the polyacrylic anion exchangers of the weakly basic functional groups Amberlite IRA 67 and of the intermediate base Amberlite IRA 478RF dropped from 9.98 mg/g to 9.2 mg/g and from 9.98 to 8.9 mg/g, respectively. The effect of Na2SO4 concentration on C.I. Acid Orange 7 removal using the strongly basic anion exchangers of the polyacrylic skeleton (Amberlite IRA 458 and Amberlite IRA 958) was insignificant. Similar observation of the effect of salts addition such as Na2HPO4 and NaH2PO4 was observed by Greluk and Hubicki [29]. In the presence of NaH2PO4 and Na2HPO4, the C.I. Acid Orange 7 retention by Amberlite IRA 958, in the system 200 mg/L dye and 0.1–2.0 g/L salts was not affected. Using weakly (Lewatit MonoPlus MP 62), intermediate (Lewatit MonoPlus MP 64) and strongly (Lewatit MonoPlus MP 500, Lewatit MonoPlus M 500, Lewatit MonoPlus M 600, Amberlite IRA 900 and Amberlite IRA 910) basic anion exchangers of the polystyrene–divinylbenzene matrix negligible influence of Na2SO4 addition in the range of 1–25 g/L on C.I. Acid Orange 7 uptake was observed. Quantitative removal of C.I. Acid Orange 7 of the initial concentration 200 mg/L from the system containing 0.1–2.0 g/L of NaH2PO4 and Na2HPO4 using strongly basic anion exchangers of type 1 Amberlite IRA 900 and of type 2 Amberlite IRA 910 was reported by Greluk [30].

The removal of C.I. Acid Orange 7 in the presence of sodium chloride even at relatively high concentration of 50 g/L was quantitative using all applied anion exchangers.

The removal of C.I. Acid Orange 7 from the solutions containing from 0.5 to 2.0 g/L of acetic acid was also studied. As shown in Figures 7 and 8, the amounts of the dye retained by the polystyrene and polyacrylic anion exchangers of various basicity decrease with the increasing amount of CH3COOH in the system. The differences between the sorption capacities deter‐ mined in the systems without the acetic acid and in the systems containing this acid do not exceed 15%. The same behaviour of the phenol–formaldehyde anion exchanger Amberlyst A 23 towards C.I. Acid Orange 7 was observed in the presence of the acid.

Direct dyes like the acid ones belong to strong electrolytes and are completely dissociated in water baths into coloured anions and sodium cations:

$$D^{Z^-} (Na^+)\_Z \leftrightarrow D^{Z^-} + zNa^+$$

The second group includes dyes of more developed molecules and greater affinity for wool. They are used for dyeing in the baths of pH 4.5–5 acidified with acetic acid. The third group has badly equalizing dyes of largely expended molecules and great affinity for wool. They are applied for dyeing in the baths of pH 5.5–6.5 in the presence of ammonium salts (sulfate, acetate), which decompose only at increased temperature acidifying the bath. Usually, sodium sulfate is added to the dyeing bath in the amount 10–20% in the proportion to the fibre and 1–

The influence of inorganic salts such as NaCl and Na2SO4 on the sorption of C.I. Acid Orange 7 from the solution of the initial concentration 100 mg/L was studied. The results indicate that the presence of these salts in the whole examination concentration of 1–25 g/L does not affect the dye adsorption significantly. In the case of the increasing amount of sodium sulfate in the solution from 1 to 25 g/L, the anion exchange capacities of the polyacrylic anion exchangers of the weakly basic functional groups Amberlite IRA 67 and of the intermediate base Amberlite IRA 478RF dropped from 9.98 mg/g to 9.2 mg/g and from 9.98 to 8.9 mg/g, respectively. The effect of Na2SO4 concentration on C.I. Acid Orange 7 removal using the strongly basic anion exchangers of the polyacrylic skeleton (Amberlite IRA 458 and Amberlite IRA 958) was insignificant. Similar observation of the effect of salts addition such as Na2HPO4 and NaH2PO4 was observed by Greluk and Hubicki [29]. In the presence of NaH2PO4 and Na2HPO4, the C.I. Acid Orange 7 retention by Amberlite IRA 958, in the system 200 mg/L dye and 0.1–2.0 g/L salts was not affected. Using weakly (Lewatit MonoPlus MP 62), intermediate (Lewatit MonoPlus MP 64) and strongly (Lewatit MonoPlus MP 500, Lewatit MonoPlus M 500, Lewatit MonoPlus M 600, Amberlite IRA 900 and Amberlite IRA 910) basic anion exchangers of the polystyrene–divinylbenzene matrix negligible influence of Na2SO4 addition in the range of 1–25 g/L on C.I. Acid Orange 7 uptake was observed. Quantitative removal of C.I. Acid Orange 7 of the initial concentration 200 mg/L from the system containing 0.1–2.0 g/L of NaH2PO4 and Na2HPO4 using strongly basic anion exchangers of type 1 Amberlite IRA 900

The removal of C.I. Acid Orange 7 in the presence of sodium chloride even at relatively high

The removal of C.I. Acid Orange 7 from the solutions containing from 0.5 to 2.0 g/L of acetic acid was also studied. As shown in Figures 7 and 8, the amounts of the dye retained by the polystyrene and polyacrylic anion exchangers of various basicity decrease with the increasing amount of CH3COOH in the system. The differences between the sorption capacities deter‐ mined in the systems without the acetic acid and in the systems containing this acid do not exceed 15%. The same behaviour of the phenol–formaldehyde anion exchanger Amberlyst A

Direct dyes like the acid ones belong to strong electrolytes and are completely dissociated in

( ) -+ - + « + *Z Z D Na D zNa <sup>Z</sup>*

2% of formic, acetic or sulfuric acid.

56 Ion Exchange - Studies and Applications

and of type 2 Amberlite IRA 910 was reported by Greluk [30].

concentration of 50 g/L was quantitative using all applied anion exchangers.

23 towards C.I. Acid Orange 7 was observed in the presence of the acid.

water baths into coloured anions and sodium cations:

**Figure 7.** Influence of acetic acid concentration on C.I. Acid Orange 7 uptake by the anion exchangers of the polystyr‐ ene matrix

**Figure 8.** Influence of acetic acid concentration on C.I. Acid Orange 7 uptake by the anion exchangers of the polyacrylic matrix

where *Dz*– – the dye anion, *z* – the numer of sulfonic groups.

Flat structure and large molecular mass (usually 600-1000) of direct dyes make their tendency to form associated ions (colloidal electrolytes):

$$nD^{Z^{-}} \leftrightarrow (D^{Z^{-}})\_{\pi}$$

where *n* – the association degree [14].

Association degree decreases with the increasing temperature. Alkalizing bath also promotes decomposition of associates; therefore, sodium carbonate is often added to the dyeing bath. Large negative charge of direct dye anions (2–4 sulfonic groups) causes that in the water bath they are repelled by the fibre surfaces of the negative electrokinetic potential dzeta. The addition of electrolyte, most frequently sodium sulfate or sodium chloride, decreases the negative potential dzeta facilitating the access of dye anions to the fibre surface. The dyeing bath contains (in the percentage of the dyeing product amount) from 0.5% to 2% Na2CO3 and 4–30% Na2SO4 depending on the method of dyeing and intensity of colour [14]. Removal of C.I. Direct Blue 71 from the systems containing 100 mg/L of dye and 1–25 g/L of NaCl and Na2SO4 on the weakly, intermediate and strongly basic anion exchangers was broadly described in the papers [20] and [25]. For the intermediate (Amberlite IRA 478RF) and strongly basic (Amberlite IRA 958 and IRA 458) anion exchangers of the polyacrylic matrix, the presence of NaCl and Na2SO4 in the whole examined concentration range of 1–25 g/L did not influence the adsorption capacities. The dye sorption was quantitative. The above mentioned anion exchangers have the same constitution of matrix, but different structure (gel or macroporous). Amberlite IRA 67 being of the same constitution of matrix and gel structure but of the tertiary amine functionalities exhibited insignificant drop of the sorption capacity with the increasing amount of electrolytes [20, 25]. It can be concluded that in the case of the polyacrylic anion exchange resins of different basicity, no significant influence of matrix structure was observed. Insignificant drop of the anion exchange capacities of Amberlyst A 23 towards C.I. Direct Blue 71 with the increasing amount of electrolytes was noticed, too.

The effect of the presence of NaCl and Na2SO4 on C.I. Direct Blue 71 sorption on the gelular polystyrene strongly basic anion exchangers of type I (Lewatit MonoPlus M 500) and type II (Lewatit MonoPlus M 600) was rather negligible. For Lewatit MonoPlus M 500, the increase in the amount of dye adsorbed at the equilibrium from 2.2 to 3.0 mg/g and from 2.2 to 2.8 mg/ g was observed with the increasing NaCl and Na2SO4 concentration from 1 to 25 g/L, respec‐ tively. In the systems of the composition 100 mg/L – 1–25 g/L electrolyte – Lewatit MonoPlus M 600, the values of *qe* ranged from 1.3 to 2.6 mg/g and from 1.3 to 2.4 mg/g with ranging concentrations of NaCl and Na2SO4, respectively. Gel structure of both anion exchangers hindered diffusion of C.I. Direct Blue 71 anions to the pores and interactions with the -N+ (CH3)3 or -N+ (CH3)2C2H4OH functional groups. The type of the functional groups of these strongly basic anion exchangers is of no significance as far as the removal of C.I. Direct Blue 71 is concerned.

A remarkable increase of adsorption capacities was observed during the dye uptake by the polystyrene anion exchangers of macroporous structure and different basicity of functional groups. The dye uptake by the weakly basic anion exchanger Lewatit MonoPlus MP 62 was increased in the presence of salts, the values of *qe* increase from 5.86 mg/g to 9.9 mg/g with the increasing concentration of both electrolytes. The sorption enhancement of Lewatit MonoPlus MP 64 was observed from 1.9 to 9.97 mg/g and from 1.9 to 9.95 mg/g with the increasing concentration of NaCl and Na2SO4, respectively. At the equilibrium, the sorption capacities of Lewatit MonoPlus MP500 increase from 1.89 to 9.98 mg/g and from 1.89 to 9.95 mg/g with the increasing amount of NaCl and Na2SO4 in the range of 1–25 g/L, respectively. For Amberlite IRA 900 of the -N+ (CH3)3 functional groups and Amberlite IRA 910 of the -N+ (CH3)2C2H4OH functional groups, sorption capacities increased from 6.9 to 9.9 mg/g and from 5.9 to 9.2 mg/g with the increasing amount of NaCl in the solution. Similar dependences were noticed in the presence of Na2SO4, the addition of 25 g/L Na2SO4 enhanced the sorption yield of Amberlite IRA 900 and IRA 910 by about 36% and 30% compared with the systems without this salt.

Reactive dyes contain in their structure a system of atoms which can form covalent bonds with hydroxyl groups of cellulose. Hydroxyl groups of cellulose react with reactive systems in dye molecules according to the nucleophilic substitution mechanism (e.g. dyes with the symmetric triazine system) or nucleophilic attachment (residue of ethylsulfone sulfates). The alkaline medium (5–20 g/L Na2CO3) is the condition for the dye reaction with a fibre. To enhance it, the electrolyte in the form of sodium sulfate in the amount from 15 to 100 g/L depending on a dye is added to the bath [14]. The effect of sodium sulfate and sodium carbonate on the reactive dye adsorption on the anion exchangers was investigated in the salts concentration range 1– 25 g/L with the constant initial C.I. Reactive Black 5 concentration of 100 mg/L.

Increasing amount of sodium sulfate and sodium carbonate in the system, insignificant decrease of the sorption capacities of Amberlite IRA 67, Amberlyst A 23, Lewatit MonoPlus MP 62 and Lewatit MonoPlus MP 64 were observed. Our previous studies revealed that in the 1000 mg/L C.I. Reactive Black 5 – 50-100 g/L Na2SO4 (or Na2CO3) system uptake of the reactive dye slightly increased by Amberlite IRA 67 [23]. C.I. Reactive Black 5 retention by the Amberlite IRA 478 RF, Amberlite IRA 458, Amberlite IRA 958 of the polyacrylic matrix and by Amberlite IRA 900 and IRA 910, Lewatit MonoPlus MP 500 of the polystyrene matrix was not affected in the presence of Na2SO4 and Na2CO3. It was reported by Greluk [30, 31] that the sorption capacities of Amberlites IRA 458 and IRA 958 devaluate about 2% in the presence of 100 mg/L of Na2CO3. The presence of NaCl in the range 25–100 g/L in the solution containing 200 mg/L of C.I. Reactive Black 5 caused significant decrease in the amount of the dye retained by Amberlite IRA 478RF according to Wawrzkiewicz [20]. The addition of Na2SO4 and Na2CO3 in the amount of 25 g/L enhanced adsorption capacities of Lewatit MonoPlus M 500 to C.I. Reactive Black 5 from 1.3 to 1.69 mg/g and from 1.3 to 1.72 mg/g, respectively. There was also noticed the increase of the amount of dye sorbed by Lewatit MonoPlus M 600 from the values 0.87 to 1.1 mg/g and from 0.87 to 1.2 mg/g with the increasing amount of sodium sulfate and sodium carbonate from 1 to 25 g/L, respectively.

Summing up, it could be stated that:

where *Dz*–

58 Ion Exchange - Studies and Applications

or -N+

concerned.

– the dye anion, *z* – the numer of sulfonic groups.

71 with the increasing amount of electrolytes was noticed, too.

to form associated ions (colloidal electrolytes):

where *n* – the association degree [14].

Flat structure and large molecular mass (usually 600-1000) of direct dyes make their tendency

( ) *Z Z* - - « *<sup>n</sup> nD D*

Association degree decreases with the increasing temperature. Alkalizing bath also promotes decomposition of associates; therefore, sodium carbonate is often added to the dyeing bath. Large negative charge of direct dye anions (2–4 sulfonic groups) causes that in the water bath they are repelled by the fibre surfaces of the negative electrokinetic potential dzeta. The addition of electrolyte, most frequently sodium sulfate or sodium chloride, decreases the negative potential dzeta facilitating the access of dye anions to the fibre surface. The dyeing bath contains (in the percentage of the dyeing product amount) from 0.5% to 2% Na2CO3 and 4–30% Na2SO4 depending on the method of dyeing and intensity of colour [14]. Removal of C.I. Direct Blue 71 from the systems containing 100 mg/L of dye and 1–25 g/L of NaCl and Na2SO4 on the weakly, intermediate and strongly basic anion exchangers was broadly described in the papers [20] and [25]. For the intermediate (Amberlite IRA 478RF) and strongly basic (Amberlite IRA 958 and IRA 458) anion exchangers of the polyacrylic matrix, the presence of NaCl and Na2SO4 in the whole examined concentration range of 1–25 g/L did not influence the adsorption capacities. The dye sorption was quantitative. The above mentioned anion exchangers have the same constitution of matrix, but different structure (gel or macroporous). Amberlite IRA 67 being of the same constitution of matrix and gel structure but of the tertiary amine functionalities exhibited insignificant drop of the sorption capacity with the increasing amount of electrolytes [20, 25]. It can be concluded that in the case of the polyacrylic anion exchange resins of different basicity, no significant influence of matrix structure was observed. Insignificant drop of the anion exchange capacities of Amberlyst A 23 towards C.I. Direct Blue

The effect of the presence of NaCl and Na2SO4 on C.I. Direct Blue 71 sorption on the gelular polystyrene strongly basic anion exchangers of type I (Lewatit MonoPlus M 500) and type II (Lewatit MonoPlus M 600) was rather negligible. For Lewatit MonoPlus M 500, the increase in the amount of dye adsorbed at the equilibrium from 2.2 to 3.0 mg/g and from 2.2 to 2.8 mg/ g was observed with the increasing NaCl and Na2SO4 concentration from 1 to 25 g/L, respec‐ tively. In the systems of the composition 100 mg/L – 1–25 g/L electrolyte – Lewatit MonoPlus M 600, the values of *qe* ranged from 1.3 to 2.6 mg/g and from 1.3 to 2.4 mg/g with ranging concentrations of NaCl and Na2SO4, respectively. Gel structure of both anion exchangers hindered diffusion of C.I. Direct Blue 71 anions to the pores and interactions with the -N+

(CH3)2C2H4OH functional groups. The type of the functional groups of these strongly basic anion exchangers is of no significance as far as the removal of C.I. Direct Blue 71 is

(CH3)3


F– < ClO3 – < BrO3 – < HCOO– < IO3 – <CH3COO– < H2PO4 – < HCO3 – < Cl– < CN– < NO2 – < Br– < NO3 – < HPO4 2– < SO3 2– < SO4 2– < C2O4 2– < CrO4 2– < MoO4 2– < WO4 2– < S2O3 2– < I– < SCN– < ClO4 – < salicylate < citrate < OH–

and towards the strongly basic anion exchangers:

OH– < F– < ClO3 – < BrO3 – < HCOO– < IO3 – <CH3COO– < H2PO4 – < HCO3 – < Cl– < CN– < NO2 – < Br– < NO3 – < HPO4 2– < SO3 2– < SO4 2– < C2O4 2– < CrO4 2– < MoO4 2– < WO4 2– < S2O3 2– < I– < SCN– < ClO4 – < salicylate < citrate


Wastewater and after-process water from textile plants can contain surface-active substances. Surfactants are often applied as wetting, penetrating, dispersing and leveling agents in dyeing processes. They increase the solubility of dyes in water, in order to improve the dye uptake and dye fastness. Many articles published recently about the treatment of textile wastewaters focused on dyes removal and often neglected the influence of surfactant. Effect of the addition of such surfactants as sodium dodecyl sulfate (SDS) or cetyltrimethylammonium bromide (CTAB) on the dye removal by the used anion exchangers was studied from the systems containing 100 mg/L of dye in the presence of 0.1–1 g/L SDS or CTAB.

Investigating the uptake of C.I. Acid Orange 7, C.I. Reactive Black 5 and C.I. Direct Blue 71 by the applied weak, intermediate and strong base anion exchangers from the systems containing 100 mg/L of the dye in the presence of the cationic surfactant CTAB, major decrease in the sorption capacities with the increasing concentration of CTAB from 0.1 to 1 g/L was observed. The attractive interactions between the dyes anions and positively charged head group of CTAB caused the formation of different types of aggregates (micelles) depending on the ratio of the dye to surfactant and decreasing concentrations of "free" dye anions in the aqueous phase at the same time. In case of anion exchangers' interaction with dyes, these observations were described by Greluk and Hubicki [29, 31], Greluk [30] and Wawrzkiewicz [15, 20, 23]. Sorption of basic and acid dyes on different low-cost sorbents like chemically treated wood shavings, iron humate as well as oxihumolite in the presence of different surfactants was explained in detail by Janoš [37] and Janoš et al. [38-40].

The anionic surfactant SDS affected the dye sorption in three ways: no impact on the dyes uptake, decrease in the dyes uptake or enhanced dyes uptake as shown in Figure 9. The first mentioned behavior was observed during the sorption of C.I. Acid Orange 7 (100 mg/L) from the solutions containing 0.1–2 g/L SDS not only for the polystyrene anion exchangers but also for the polyacrylic ones (Figure 9 a) and b)).

Decreasing of the anion exchange capacities with the increasing amounts of SDS can be explained as a competition of adsorption sites between these species compared with dyes anions causing reduction of the dye uptake. For example, the sorption of C.I. Reactive Black 5 (Figure 9 c) and d)) was slightly reduced with the increasing amount of SDS in the system for the most of weakly and strongly basic anion exchangers of the polystyrene matrix. Both C.I. Reactive Black 5 and SDS are negatively charged and the interactions between the anionic SDS and the dye anions must be repulsive, independent of the surfactant concentration. Competi‐ tion between these species of adsorption sites caused reduction of the dye uptake.

For the polystyrene anion exchangers of macroporous structure, i.e. Lewatit MonoPlus MP 62, MP 64, MP 500 and Amberlite IRA 900 a diverse trend was found (Figure 9 e) and f)) in the case of C.I. Direct Blue 71 sorption. Increasing the concentration of SDS in the range 0.1–1 g/L, enhancement of the dye anions sorption was observed. The surfactant can be adsorbed on the active sites or on the hydrophobic parts of the matrix of the anion exchangers in the form of relatively small poor ordered surface aggregates and interact with the aromatic rings or anionic groups of the dye.
