Study on the extraction of dyes into a room-temperature ionic liquid and their mechanisms

The investigation of liquid-liquid extraction of dyes is carried out by using ionic liquid - 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF₆]) - as extraction phase. The effects of its process parameters are studied in detail, such as extraction phase ratio, pH of the aqueous phase, and concentration of dicyclohexyl-18-crown-6 (DCH-18C6) in the organic phase. Important results are obtained as follows: acid dyes can be extracted with [BMIM][PF₆] quantitatively; the removal of reactive dyes is low; however, it can be greatly increased by the addition of DCH-18C6. The pH value has a great impact on the removal of the acid dye and the reactive dye. However, it does not influence the extraction of the weak acid dye. It is found that the extraction process of acid dyes adopts the form of anion exchange and the soluble part of the ionic liquid plays an important role as counter-ions.