Reversible dye extraction from aqueous matrices using ammonium salt-based deep eutectic solvents

Recovery of dyes present in liquid solutions was achieved with efficiencies higher than 99 %, using deep eutectic solvents composed of tetrabutylammonium chloride and decanoic acid. The method produces a totally decolorized water. Both the reuse of the clean water and of the extracted dye is plausible via this treatment, as the colorant can be recovered from the organic phase after the liquid–liquid extraction. The solvent is physically and chemically characterized, in a wide arrange of temperatures, and its behavior in liquid–liquid equilibria with water was also studied. The process works for a broad range of dye concentrations, and with a very low consumption of solvent (optimized volumetric ratio between organic and aqueous phases was 1/16). Optimized processing times set the duration of the treatment at 20 min, including the recovery of the dye from the extracted phase. The capabilities of the solvent were tested against synthetic effluents composed by industrial dyes and auxiliary agents that typically appear on dyeing processes, maintaining efficiencies above 99 %. The deep eutectic solvents also work equally well for extracting mixtures of dyes.