Separation of Anionic Chlorinated Dyes from Polluted Aqueous Streams Using Ionic Liquids and Their Subsequent Recycling

Abstract

The effect of ionic liquids on the separation of chlorinated anionic dyes such as Mordant Blue 9 (MB9) or Acid Yellow 17 (AY17) via ion exchange has been investigated in model aqueous solutions that simulate wastewater from the textile dyeing industry. The effect of ionic liquids chemical nature on the separation efficiency of mentioned dyes has been compared. It was found that especially ionic liquid based on quaternary ammonium salts comprising two or three long alkyl chains bound to the quaternary ammonium nitrogen (typically benzalkonium chloride or Aliquat 336) are very effective for the separation of both studied MB9 and AY17 from aqueous solution. In addition, the innovative technique has been developed for the reactivation of spent ionic liquids which is based on the chemical reduction of the formed ion pairs using NaBH4/NiSO4, NaBH4/Na2S2O5 or Raney Al-Ni alloy/NaOH. Thus, only NaBH4/NiSO4 in co-action with Al-Ni alloy enables both effective reduction of the azo bond and subsequent hydrodechlorination of emerging chlorinated aromatic amines. The efficiency of tested dyes separation or regeneration of ion pairs was evaluated by determination of the absorbance at wavelength of the maximum absorbance, of the Chemical Oxidation Demand (COD), and of the Adsorbables Organically bound Halogens (AOX). The formation of ion pairs or products of reduction and hydrodechlorination of these ion pairs has been studied using the 1H NMR and LC-MS techniques.

Co-Action of Ionic Liquids with Alternative Sorbents for Removal of Reactive Azo Dyes from Polluted Wastewater Streams

“…(b) The rapid formation of less polar ion pairs: The formation of water-insoluble ion pairs was discussed in Section 3.2. Separation of RB8 using ILs above and was also proved in our previous studies [44,45] using analytical techniques such as NMR. (c) (i) In the case of BC application, the better affinity of formed ion pairs to the BC surface: As Gray et al [59] suggested, the biochar-based sorbents show rather the non-polar nature of its surface.…”

“…The better separation of RB8 using BAC can be caused by the better solubility of BAC in water and thus a better contact of BAC and RB8 dissolved in water. Based on these findings, BAC combines both sufficient aqueous solubility and the removal efficiency of acid halogenated pollutants such as RB8 dye; for more information, see our previous studies [32,44,45].…”

“…Our previous works [32,44,45] reported that the addition of appropriate amounts of quaternary ammonium compounds (R 4 NX, ILs) to the aqueous solutions of acidic halogenated compounds (substituted with -COO − or -SO 3 − groups), including dyes or drugs, results in ion exchange and the formation of respective insoluble ion pairs (see Equation ( 1) above and Scheme 1 below) that can be separated from aqueous solutions by simple filtration. The formation of the mentioned ion pairs has been earlier proven by NMR analysis; see refs.…”

“…The formation of the mentioned ion pairs has been earlier proven by NMR analysis; see refs. [32,44,45]. Therefore, the subsequent experiments were focused on the separation of RB8 dye using two ILs-BAC [52] and A336 [53] (for chemical drawings, see Figure 2 above).…”

“…As we previously published, anionic drugs [44] or anionic azo dyes [45] can be effectively separated from aqueous solutions using ILs based on quaternary ammonium salts (R 4 NX). This method consists in the addition of commercially available and inexpensive ILs, which is accompanied by the ion exchange of inorganic anions X − of R 4 NX with anions of acid dyes (according to Equation ( 1)), producing low-polar ion pairs (dye-SO 3 NR 4 ) insoluble in aqueous solution and separable by sedimentation and/or filtration.…”