EFFECT OF POLYELECTROLYTE CHARGE-DENSITY AND MOLECULAR-WEIGHT ON THE FLOTATION OF OIL-IN-WATER EMULSIONS

The effect of polyelectrolyte charge density and molecular weight on t he flotation of oil emulsified in aqueous electrolyte was investigated . Flotation performance improved with increasing polyelectrolyte charg e density, while polyelectrolyte intrinsic viscosity (molecular weight ) had no effect on flotation over the range 6-12 dl g(-1). Turbidity r emoval improved as flee size increased, indicating that polyelectrolyt e enhanced flotation by increasing the floc size. The trends in the fl otation and flocculation behaviour of the emulsion with changing polye lectrolyte intrinsic viscosity (molecular weight) were consistent with electrostatic patch flocculation. Raising the charge density of the o il increased the amount of polyelectrolyte required for optimal flotat ion and led to improved performance, while raising the background KNO3 concentration from 10(-3) to 10(-1) M decreased flotation performance . The effect of electrolyte concentration was greatest at low oil char ge density (pH 5) and low polyelectrolyte charge density. It is propos ed that the reduction in flotation performance with rising electrolyte concentration was due to increased electrostatic shielding leading to smaller floc sizes, as electrostatic attraction between charged patch es on the oil was thought to be the flocculation mechanism. The flotat ion process was more robust towards changes in polyelectrolyte dose wh en polyelectrolytes of lower charge density were used. (C) 1997 Elsevi er Science B.V.