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Purification of Effluents by Two-Aqueous Phase Extraction

The goal of this work is the two-aqueous phase extraction of solutes representing a soluble or dispersed pollution. This is made possible thanks to the phase separation occurring with polyefhoxylated surfactants above the so-called cloud point curve and the solubilization properties of nonionic micelles mainly present in the more concentrated surfactant phase (coacervate). The surfactants used are commercial alcohol ethoxylates ( n -C 12 E 4 , n -C 12 E 6 , Oxo-C 10 E 3 and Oxo-C 13 E 9 ). The phase diagrams of binary water/surfactant, pseudo-binary (in the presence of solute) and ternary water/surfactant/solute systems were drawn. The last three surfactants were used for the ‘cloud point’ extraction of phenol and benzyl alcohol from their 0.15 wt% aqueous solutions (soluble pollution). The polluted aqueous phase and the surfactant solution were mixed together and separated at room temperature or after heating, according to the cloud point curve of the surfactant. The results are expressed by the four following responses: percentage of solute extracted ( E ); residual concentrations of solute and surfactant in the dilute phase; and volume fraction of coacervate ( O C ) at equilibrium. For each parameter, whose values were determined by an experimental design, these results were the subject of an empirical curve fitting procedure. The best compromise was sought between E , which can be higher than 95%, and ( O C ), which must be kept to a minimum (more concentrated pollutant, easier to process). Finally, we applied this extraction technique to two types of mineral cutting oils, used in granite sawing operations. The results are then expressed as chemical oxygen demand (COD) of the dilute phase before and after extraction, and volume fraction of coacervate. For instance, COD can be reduced from 55 to 1.5 g O 2 1 –1 . Empirical modelling gives a satisfactory agreement between experimental and calculated values.