LIGAND-MODIFIED POLYELECTROLYTE-ENHANCED ULTRAFILTRATION WITH ELECTROSTATIC ATTACHMENT OF LIGANDS .1. REMOVAL OF CU(II) AND PB(II) WITH EXPULSION OF CA(II)

A water-soluble mixture of a cationic polyelectrolyte, poly(diallyldimethylammonium chloride) or PDADMAC, and an anionic ligand, 4,5-dihydroxy-1,3-benzenedisulfonic acid, or Tiron, is used as an agent for binding divalent cations, such as Cu2+ and Pb2+. In equilibrium dialysis experiments, the PDADMACT-Tiron mixture is shown to be effective in binding Cu2+ and Pb2+ in the retentate, while enhancing the concentration of the noncomplexed cation, Ca2+, in the permeate. In the pH range employed, the uncomplexed and complexed forms of Tiron exist primarily as divalent anions. As a consequence they are bound electrostatically to the cationic polyelectrolyte, and little of the ligand is lost through the membrane. The effects of pH, cation concentration, and presence of a competing cation (Ca2+), and added NaCl on the retention of Cu2+ and Pb2+ are discussed

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