Margot A. Llosa Tanco

ADSORPTION CHARACTERISTICS AND REMOVAL OF OXO-ANIONS OF ARSENIC AND SELENIUM ON THE POROUS POLYMERS LOADED WITH MONOCLINIC HYDROUS ZIRCONIUM OXIDE

Adsorption properties for oxoanions of Se(IV), Se(VI), As(III), As(V), and methyl derivatives of As(V) have been examined by the porous polymer beads loaded with monoclinic hydrous zirconium oxide (Zr-resin). The retention of these ions on the Zr-resin has been analyzed using Langmuir model of adsorption. The equilibrium constants and the capacities for above ions have been determined. The equilibrium constants for monomethyl arsinic acid and dimethyl arsinic acid are similar to that of As(V) but the adsorption capacity depends on the number of methyl groups. As(V) and Se(IV) are effectively retained on the Zr-resin from an aqueous solution of acidic to neutral pH region, whereas As(III) is removed from neutral to alkaline solution. The column system packed with the present Zr-resin can quantitatively remove low levels of As(V) and Se(IV) from aqueous solution.

Adsorption and removal of oxo-anions of arsenic and selenium on the zirconium(IV) loaded polymer resin functionalized with diethylenetriamine-N,N,N′,N′-polyacetic acid

A polymer adsorbent in which a Zr(IV)-edta complex analogue is immobilized has been prepared and applied to the removal of oxo-anions of As(III), As(V) and Se(IV). Effective retention of these anions has been demonstrated with the proposed polymer complex system. The adsorption mechanism of oxo-anions onto the Zr(IV)-chelated polymer complex has been investigated using Zr(IV)-edta as the model compound. The formation of mixed complexes with oxo-anions has been exemplified by the isolation of the carbonato complex K2[Zr(CO3)edta].3H2O, the structure of which has been confirmed by X-ray crystallography. NMR study suggests that oxo-anions that form weak or moderate conjugate acids, including those of As(III), As(V) and Se(IV), can form mixed complexes with Zr(IV)-edta using the unsaturated coordination site. However, oxo-anions of strong conjugate acids did not show any appreciable interaction with this complex. According to these observations, retention of oxo-anions on the Zr(IV)-chelated polymer complex has been interpreted by a ligand substitution reaction. The adsorption characteristics of As(III), As(V) and Se(IV) on the Zr(IV)-loaded resin have been examined with respect to the equilibrium adsorption, percentage extraction and the effect of co-existing ions. The adsorption and desorption cycles of the oxo-anions have been demonstrated using a column packed with the proposed resin without any loss of column performance, which indicates the possibility for repeated use.

Preparation of porous chelating resin containing linear polymer ligand and the adsorption characteristics for harmful metal ions

Abstract A linear copolymer consisting of maleic anhydride and methylvinylether has been immobilized on the interior surface of porous polymer beads. The modified polymer beads thus obtained have formed the starting material for the preparation of metal selective chelating resins by the reaction of the maleic anhydride moiety with appropriate ligands. Cysteamine has been grafted as the pendant ligand and the resulting chelating resin (cysteamine resin) maintains a high porosity and large specific surface area. On the basis of scanning electron microscopy (SEM) and electron dispersion X-ray (EDX) analyses, the linear polymer is distributed from the outer layer to the inner pores of the resin beads. The adsorption characteristics of the cysteamine resin for Cd 2+ and Pb 2+ have been examined with respect to the percentage extraction, adsorption isotherm and reproducibility upon adsorption–regeneration cycles. The chelating resin shows a remarkably high adsorption rate, which has been attributed to the porous nature of the resin and geometrical flexibility of the ligand. Quantitative removal of Cd 2+ and Pb 2+ from aqueous solution has been demonstrated by the column procedure packed with the cysteamine resin.

Adsorption of fluoride ion on the zirconium(IV) complexes of the chelating resins functionalized with amine-N-acetate ligands

The reaction of fluoride ion with Zr(IV)-ethylenediamine-N,N,N′,N′-tetraacetate (EDTA) complexes has been examined by 19F and 1H NMR spectroscopies and potentiometry using [Zr(H2O)2EDTA] and K2[Zr(CO3)EDTA] as the model compounds. Ternary complex formation has been suggested as the most plausible mechanism for the retention of fluoride ion on the Zr(IV) complexes. Removal of fluoride ion has been attempted by the use of polymer homologues of Zr(IV)–EDTA complexes. Adsorption characteristics of fluoride ion on Zr(IV) complexes of the chelating resins [CMA (carboxymethylamine) and IDA (iminodiacetic acid) resins] have been investigated. The adsorption capacities and the binding constants for fluoride ion on the Zr(IV) loaded resins have been analyzed using Langmuir model of adsorption. Common anions including chloride, nitrate, acetate, and sulfate ions did not interfere significantly with the adsorption of fluoride ion, whereas the presence of phosphate ion reduced the fluoride capacity markedly. The adsorption rate of fluoride ion uptake by Zr-CMA resin is much faster than that of the Zr-IDA resin. A column process including adsorption, desorption, and regeneration cycles has been demonstrated for the removal of fluoride ion to depict a practical application.

Solution and co-ordination enthalpies (solid state) of lithium and sodium macrocycle (ethyl p-tert-butylcalix(4)arene tetraethanoate, cryptand 222 and crown ethers) systems

A series of lithium and sodium ethyl p-tert-butylcalix(4)arene tetraethanoate and cryptand 222 salts has been isolated and thermochemically characterised in acetonitrile at 298.15 K. Also reported are the standard enthalpies of solution of common sodium salts (tetrafluoroborate, trifluoromethanesulfonate, iodide and bromide) in this solvent at the same temperature. Solution data for the free and the complexed salts and for the ligand are combined with complexation data for the appropriate cation and macrocycle in acetonitrile to derive the enthalpies of co-ordination of these systems for the process where the product and the reactants are in the solid state. Comparison of data involving lithium and the calix(4)arene ester and the cryptand 222 with those for crown ethers reflects considerable weakening of cation–anion interactions in the former ligands relative to crown ethers. It is concluded that for a given ligand and metal cation, the anion effect is reflected in the co-ordination enthalpies. On the other hand, for systems containing the same ligand and anion, there is a decrease in enthalpic stability in moving from lithium to sodium. The need to obtain experimental data on crystal lattice enthalpies of these ligands and their metal ion complex salts is emphasised.