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.