ABSTRACT
Haloacetic acids, formed in drinking water during disinfection by chlorination, pose significant risks to human health. Semiequilibrium dialysis and ultrafiltration experiments were used to examine the partitioning of the five regulated haloacetic acids (HAA(5)) viz. chloro-, dichloro-, trichloro-, bromo-, and dibromoacetic acids into cetylpyridinium chloride (CPC) micelles across a range of micellar mole fraction, surfactant concentration, and added NaCl conditions. The results of these experiments were successfully correlated using a nonlinear three-site equilibrium model, which combines thermodynamic relations with the Oosawa two-state binding theory, incorporates allowances for nonideality, and includes a parameter to account for haloacetate solubilization. Micellar-enhanced ultrafiltration using CPC provided excellent HAA(5) removal efficiencies of over 98%.
Subject(s)
Acetic Acid/isolation & purification , Cetylpyridinium/chemistry , Detergents/chemistry , Micelles , Dialysis/methods , Halogenation , Ultrafiltration/methodsABSTRACT
An application of polyelectrolyte-enhanced ultrafiltration utilizes cationic polyelectrolytes to electrostatically bind anionic species. The colloid and target anion are then concentrated using an ultrafilter, producing a filtrate with a lower concentration of the target. This study compared the performances of poly(4-vinylpyridine) (P4VP) and poly(diallyldimethylammonium) chloride (PDADMAC) for the removal of perchlorate. Potentiometric titration data revealed that the ionization properties of P4VP in aqueous solution vary as functions of titrant utilized, degree of protonation, and counterion concentration. The greater affinity of perchlorate over chloride for the protonated pyridine residues of P4VP provided up to 95.8% retention of perchlorate under the solution conditions investigated. Through ultrafiltration experiments, the effects solution pH, counterion concentration, and polymer concentration were examined for both P4VP and PDADMAC. In addition, the effectiveness of P4VP recovery and reuse was also assessed.
Subject(s)
Perchlorates/chemistry , Perchlorates/isolation & purification , Polyethylenes/chemistry , Polyvinyls/chemistry , Quaternary Ammonium Compounds/chemistry , Ultrafiltration/methods , Hydrogen-Ion ConcentrationABSTRACT
Inorganic ligand-modified, colloid-enhanced ultrafiltration (ILM-CEUF) is as a novel membrane-based separation method for selectively removing target ions from aqueous solution. Traditional colloid-enhanced ultrafiltration (CEUF) is a well-established membrane-based separation technique that can be used to separate metal ions from other aqueous solution components. Ligand-modified, colloid-enhanced ultrafiltration (LM-CEUF) uses organic ligands that selectively complex target ions and also associate with a water-soluble colloid, such as a surfactant micelle or polyelectrolyte. The colloid, associated -ligand, and target ion are then concentrated using an ultrafilter, producing a filtrate with a low concentration of the target ion. While traditional LM-CEUF techniques are able to provide quantitative separations of a variety of ionic pollutants, the high costs of the chelating agents make such techniques nonviable in most remediation schemes. This study investigated the replacement of organic ligands with carbonate for the selective removal of U(VI) from aqueous solution. In slightly to moderately basic solutions containing carbonate, UO(2)(CO(3))(3)(4-) can be made to dominate the U(VI) speciation. Using poly(diallyldimethylammonium) chloride, the effectiveness and efficiency of ILM-CEUF for removing U(VI) from other aqueous solution components was investigated as a function of carbonate concentration, pH, and ionic strength. Uranium separations of greater than 99.6% were achieved; even in the presence of large excesses of competing ions. The specific separation of U(VI) from Sr(2+) was also examined.
Subject(s)
Colloids/chemistry , Uranium/isolation & purification , Water Pollutants, Radioactive/isolation & purification , Water Purification/methods , Algorithms , Hydrogen-Ion Concentration , Inorganic Chemicals/chemistry , Kinetics , Ligands , Models, Chemical , Ultrafiltration/methods , Uranium/chemistry , Water Pollutants, Radioactive/chemistry , Water Pollution, Radioactive/analysis , Water Pollution, Radioactive/prevention & controlABSTRACT
Use of perchlorate salts in military activities and the aerospace industry is widespread. These salts are highly water-soluble and are, to a large extent, kinetically inert as aqueous species. As a groundwater contaminant, perchlorate is now being detected in an increasing number of locations and is believed to interfere with the uptake of iodide by the thyroid, which can result in decreased hormone production. The United States Environmental Protection Agency (US EPA) has established a reference dose for perchlorate of 0.0007 mg/kg/day, which translates to a drinking water equivalent level of 24.5 ppb. This study investigated the application of polyelectrolyte-enhanced ultrafiltration (PEUF) for the selective removal of perchlorate from aqueous solution through equilibrium dialysis and ultrafiltration experiments. Using poly(diallyldimethylammonium) chloride, the effectiveness and efficiency of PEUF in the removal of perchlorate from other aqueous solution components was investigated by testing parameters such as polyelectrolyte concentration, pH, and ionic strength. Removal of perchlorate from synthetic groundwater initially containing 10.3 ppm perchlorate and also containing chloride, sulfate, and carbonate was also examined. Perchlorate separations of greater than 95% were achieved, even in the presence of 10-fold excesses of competing ions.
