Dynamics of nonionic surfactant-rich phase separation and recovery of dyes.

Abstract

Cloud point separation of selected dyes was studied. The use of dyes made possible observation of the dynamics of surfactant-rich phase separation by color video. The pictures were interpreted by means of ImageC software and degrees of whiteness were calculated. It was found that separation was slow and equilibrium was not achieved even after a period of more than 10 h. The separated surfactant-rich phase had a heterogeneous structure. The globules of the surfactant-rich phase were also observed in the micellar aqueous phase. The surfactant concentration could be as high as one or two orders of magnitude above the expected cmc values and was not decreased to critical micelle concentration by centrifugation. The presence of sodium chloride was important and improved separation. Separation of dyes was in the range 73-98% and depended upon the surfactant, the temperature, the electrolyte content, and the dye. In each system considered, appropriate conditions had to be selected to obtain high recovery of the dye. The presence of the electrolyte was the most important parameter and it improved the separation of dyes. However, addition of the electrolyte could also account for precipitation of the dyes, as observed for the systems containing Direct Pink. The best recoveries were observed for Direct Yellow and oxyethylated nonylphenol (98% at 55 degrees C in the presence of NaCl). Centrifugation gave recoveries similar to those for prolonged heating but it shortened the time of phase separation.