**8. Conclusions**

(after 12 h) in the case of wastewater containing Synazol Yellow KHL, SynazolBlue KBR and Synazol Red K3BS (Figure 11 c)). As shown in Figure 11 d), after 3 h of phase contact time the yield of decolourization was 88.3%, the increasing phase contact time to 144 h did not increase

The regeneration step is the key to the implementation of the anion exchange system on the commercial scale. Desorption studies help to evaluate the nature of adsorption process. Desorption experiments were performed using different regenerating agents such as 1 M NaCl, 1 M Na2SO4, 1 M Na2CO3, 1 M NaOH, 1 M HCl and even 1 M KSCN. As previously stated [2, 15, 20, 23, 25–31], the aqueous solutions mentioned above were ineffective for the dyes removal

**Figure 11.** Influence of phase contact time on the purification of raw textile effluents of different compositions using Amberlite IRA 958: a) the absorbance values at max wavelength at 0 h and 1 h were recorded after ten times repeated dilution, b) and c) samples were not diluted before measurements, d) the absorbance values at max wavelength at 0 h

the adsorption efficiency significantly.

**7.5. Desorption studies**

66 Ion Exchange - Studies and Applications

from the resin phase.

was recorded after twice repeated dilution

The possibility of the removal of C.I. Acid Orange 7, C.I. Reactive Black 5 and C.I. Direct Blue 71 using weakly (Amberlite IRA 67, Lewatit MonoPlus MP 62, Amberlyst A 23), intermediate (Lewatit MonoPlus MP 64 and Amberlite IRA 478RF) and strongly (Amberlite IRA 458, Amberlite IRA 958, Amberlite IRA 900, Amberlite IRA 910, Lewatit MonoPlus MP 500, Lewatit MonoPlus M 500 and Lewatit MonoPlus M 600) basic anion exchangers of the polyacrylic, polystyrene and phenol–formaldehyde skeletons and different matrix structure from aqueous solutions and wastewaters were discussed [2, 15, 20, 23, 25–28, 34–36]. Not only the number of sulfonic groups, position of the anionic charges, whole structure of the dyes and their molecular weight but also type of the anion exchangers determined the dyes removal by these sorbents.

Based on the values of the monolayer sorption capacities towards C.I. Acid Orange 7 (1370.4 mg/g), C.I. Reactive Black 5 (1655.2 mg/g) and C.I. Direct Blue 71 (1630.6 mg/g), it seems that the macroporous anion exchanger Amberlite IRA 958 can be a promising adsorbent for the textile wastewater treatment.

The affinity series of the dyes for Amberlite IRA 958 of quaternary ammonium functionality can be presented as follows:

C.I. Reactive Black 5 > C.I. Direct Blue 71 > C.I. Acid Orange 7.

Its advantageous behaviour for the acid, reactive and direct dyes resulted from combination of such properties as positive charge of functional groups and large pores of hydrophilic polyacrylic matrix. The experimental data indicated that the amounts of dyes adsorbed on the anion exchange resins are influenced by many factors such as initial dye concentration, phase contact time, solution pH, auxiliaries presence (NaCl, Na2SO4, Na2CO3, CH3COOH and surfactants) and their concentrations. The reversibility of adsorption depends on whether the predominant mechanism is a strong binding bond such as ionic bonding or weak binding forces such as van der Waals interactions or H-bonding and occurred with high yield using sodium hydroxide or hydrochloric acid (or potassium thiocyanate) in methanol. The adsorp‐ tion behaviour of Amberlite IRA 958 demonstrates that it can be a promising adsorbent for the textile wastewater treatment.
