Ligand-Modified Colloid Enhanced Ultrafiltration. Use of Nitrilotriacetic Acid Derivatives for the Selective Removal of Lead from Aqueous Solution

Abstract

In ligand-modified, colloid-enhanced ultrafiltration (LM-CEUF), a ligand that selectively complexes target ions (e.g., lead) also associates with a water-soluble colloid, such as a surfactant micelle or polyelectrolyte. The colloid, associated ligand, and target ion are then concentrated using ultrafiltration, producing a filtrate with a low concentration of the target ion. Dialysis, ultrafiltration, and potentiometric titration experiments have been used to investigate the effectiveness of four nitrilotriacetic acid (NTA) derivatives in the removal of lead from aqueous solution through LM-CEUF. The ligands are 2-phenyl nitrilotriacetic acid (PNTA), 2-[N, N-di-(carboxymethyl)]amino-octanoic acid (HNTA), 2-[N,N-di-(carboxymethyl)]amino-dodecanoic acid (DNTA), and 2-[N,N-di-(carboxymethyl)]amino-3-sulfopropionic acid (SNTA). The colloids used were the cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDADMAC) and the cationic surfactant cetylpyridinium nitrate (CPNO₃). In equilibrium dialysis and ultrafiltration (UF) experiments, SNTA and PDADMAC systems provided effective lead removal. In semiequilibrium dialysis and UF experiments, DNTA and CPNO₃ systems also provided effective lead removal. The effects of pH, ionic strength, competing ions, and colloid concentration were investigated for each ligand system. Ligand protonation constants and ligand–metal stability constants were obtained for SNTA in both water and solutions of PDADMAC and for DNTA in solutions of CPNO₃. Ligand regeneration through pH adjustment and metal precipitation with various anions was also demonstrated.

Acknowledgments

Financial support for this work was provided by the Department of Energy Office of Basic Energy Sciences, Grant No. DE-FG05-87ER13678; Department of Energy Environmental Management Science Program, Grant No. DE-FG07-97ER14825; the National Science Foundation, Grant No. CTS 9123388; and by the sponsors of the Institute for Applied Surfactant Research at the University of Oklahoma including Akzo Nobel Chemicals Inc., Albemarle Corporation, Amway Corporation, Clorox Company, Colgate-Palmolive, Dial Corporation, Dow Chemical Company, DowElanco, E. I. DuPont de Nemours & Co., Halliburton Services Corp., Henkel Corporation, Huntsman Corporation, ICI Americas Inc., Kerr-McGee Corporation, Lubrizol Corporation, Nikko Chemicals, Phillips Petroleum Company, Pilot Chemical Company, Procter & Gamble Company, Reckitt Benckiser North America, Schlumberger Technology Corp., Shell Chemical Company, Sun Chemical Corporation, Unilever Inc., and Witco Corporation. John Scamehorn holds the Asahi Glass Chair in chemical engineering at the University of Oklahoma.