Ultrafiltration of inorganic salts in the presence of polyelectrolytes

In the present study ultrafiltration (UF) of inorganic salts in the presence of a polyelectrolyte in the feed solution was investigated. Cellulose acetate membranes completely impermeable to the polyelectrolyte were selected with pore size 5–20 nm. At low concentrations of polyelectrolyte, a gel layer on the membrane surface does not form. At such low polyelectrolyte concentrations the concentration of inorganic salt in the permeate stream can be higher than in the feed solution. This salt concentration effect is the reverse of what is obtained with conventional membrane processes; where the permeate salt concentration is lower, or equal, to the salt concentration in the feed solution. It is shown that when ultra-filtering inorganic salts in the presence of a polyelectrolyte, the ratio of salt concentration in the permeate to feed is improved when the initial salt concentration in the feed solution is low. [Continues.]