COMPLEX DERIVED FROM THE MEDIUM ANIONIC POLYELECTROLYTE AND MEDIUM CATIONIC SURFACTANT - A NEW COAGULANT USED FOR WASTEWATER TREATEMENT

This paper aims at studying some complex coagulants derived from the medium anionic polymer and medium cationic surfactant in order to evaluate the opportunity to use them in destabilizing and removing the colloidal systems from water and wastewater. In this respect, medium anionic copolymers of acrylamide and sodium acrylate with commercial Preastol 2540, and a medium cationic surfactant derived from triethanolamine with commercial name of Tetranyl AT-7590 were used in order to obtain these complex coagulants. The formation of the complex coagulants was revealed based on a comparative analysis of some critical concentrations such as critical aggregation concentration and critical micellar concentration corresponding to both polyelectrolyte and surfactant solutions and critical aggregation concentration and critical saturation concentration corresponding to the complex solution. The values of these critical concentrations were determined from experimental data regarding the variation of the surface tension of solutions as function of their concentration. The experimental data revealed that for a constant polyelectrolyte concentration lower than the critical micellar concentration and a variable surfactant concentration, the surface tension of the complex solutions remains constant up to a surfactant concentration corresponding to its critical aggregation concentration. After this value of the surfactant concentration, the surface tension of the complex solutions significantly decreases up to a value of the surfactant solution concentration close to its critical micellar concentration and corresponding to the critical saturation concentration of the complex solutions. These results suggest the formation mechanism of the complex by grafting of surfactant micelles on the chain of the polyelectrolyte. Decreasing the surface tension of complex solutions as compared to pure polyelectrolyte solutions leads to a better development of solid-liquid interface processes that occur during coagulation-flocculation. Interactions between surfactant micelles and polyelectrolyte lead to a change in rheological properties of the solution. To get more insights concerning the flow behaviour of complex resulted from these interactions, a rheological study was performed. In this respect, both polyelectrolyte and complex solutions were characterized by determining their rheograms. The experimental results suggested that the Praestol 2540 solution is of Bingham pseudoplastic type. These rheological properties of complex solutions confer a beneficial effect on the interaction between colloidal particles and complex coagulant and subsequently, on the entire coagulation-flocculation process.