The role of anionic substances in removal of textile dyes from solutions using cationic flocculant

The mechanism of dye removal from textile waste water using polyquaternary ammonium salt as a flocculant has been proposed. It was shown that the cationic polymer tends to react with anionic textile finishing chemicals and auxiliaries (anionic detergents, dispersing agents, thickeners), forming intermolecular complexes of different stoichiometry. Under controlled conditions these complexes are able to incorporate the dye ions or molecules and precipitate together. Formation of triple complexes is postulated to be the only possible way for non-ionic dyes to be precipitated. The nature of forces causing the transfer of the dyes to a polymeric matrix has been revealed. The necessity of an anionic polyfunctional compound with a proper chemical structure to play the role of disperse dye carrier is emphasised. The mechanism of incorporation of dye ions into triple complexes, the possibility of competitive reactions, and the problems of stability and reduced cationic functionality of nonstoichiometric complexes are discussed. (C) 2002 Elsevier Science B.V. All rights reserved.