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 Cu[sup 2+] and Pb[sup 2+]. In equilibrium dialysis experiments, the PDADMAC-Tiron mixture is shown to be effective in binding Cu[sup 2+] and Pb[sup 2+] in the retentate, while enhancing the concentration of the noncomplexed cation, Ca[sup 2+], 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 (Ca[sup 2+]), and added NaCl on the retention of Cu[sup 2+] and Pb[sup 2+] are discussed. 25 refs., 4 figs., 2 tabs.