LIGAND-MODIFIED POLYELECTROLYTE-ENHANCED ULTRAFILTRATION WITH ELECTROSTATIC ATTACHMENT OF LIGANDS .2. USE OF DIETHYLENETRIAMINEPENTAACETIC ACID CATIONIC POLYELECTROLYTE MIXTURES TO REMOVE BOTH CATIONS AND ANIONS FROM AQUEOUS STREAMS

A mixture of a cationic polyelectrolyte, poly(diallyldimethylammonium chloride) or PDADMAC, and the anionic ligand diethylenetriaminepentaacetic acid (DTPA) can be added to aqueous streams as a water-soluble colloid to bind simultaneously divalent cations, such as Cu2+ and Pb2+, and anions, such as CrO42-. pH values greater than about 4, most of DTPA is attached electrostatically to the PDADMAC, so that the ligand remains in the retentate in ultrafiltration (UF) separations. Equilibrium dialysis studies show the effectiveness of the PDADMAC-DTPA mixture in binding ions of various types; the data also show that cations such as Ca2+, which do not bind to the ligand, are expelled and become concentrated in the permeate solution passing through the membrane. In equilibrium dialysis and UF experiments, with the PDADMAC-DTPA mixture added to a feed stream containing a mixture of Cu2+ and CrO42-, the bound cations and anions become highly concentrated in the retentate solution.