Dye-salt separations by nanofiltration using weak acid polyelectrolyte membranes

Separation of a dye, Cibacron blue, from a salt, NaNO3, with a common counterion by nanofiltration of dilute salt solutions containing trace concentrations of the dye using dynamically-formed weak acid polyelectrolyte membranes, was investigated. The separation factor increased with decreasing flux and ionic strength, and with increasing pH, cross flow velocity and dye-to-salt concentration ratio. The separation behavior over broad ranges of the operating parameters was described by a model requiring filtration experiments with the two electrolytes in single-solute solutions and two experiments with mixed-solute experiments to evaluate the model parameters.