Interactions of nitrates with cationic polyelectrolytes in chelation/ultrafiltration systems for water treatment

The interaction between poly(dimethylamine-co-epichlorohydrin-co-ethylene-diamine) with positive charges and nitrate ions in synthetic water was investigated during ultrafiltration (UF). The adsorption behaviour of nitrate onto cationic polyelectrolyte was evaluated with Langmuir and Freundlich isotherms in dilute polyelectrolyte solutions. During UF, ionic strength, Debye–Hückel screening length, average electric potentials at the polyelectrolyte interface, and the amount of nitrates adsorbed per mole of polymeric functional groups were estimated at different concentration factors. The results indicated that polyelectrolyte skeletons tended to coil at a higher concentration factor. It was also discovered that adsorbed nitrate was released from the polyelectrolytes while making their surface charge more positive at high concentration factors. The coiling of polyelectrolyte chains caused negative effects on the lateral interactions of nitrate with the polyelectrolyte.