Robert Gauthier

Adsorption of copper(II) and chromium(III) ions onto amidoximated cellulose

Chemical modification of cellulose powder is performed by successive reactions with acrylonitrile in an alkaline medium followed by aqueous hydroxylamine to prepare amidoximated cellulose. Due to complexation, the amidoxime groups immobilize heavy cations from buffered solutions at various pH values. The capacity of adsorption for Cu(II) and Cr(III) ions is related to the amount of amidoxime groups in the support and to the metal concentration of the polluted solution. The formation of a 1/1 complex is proved by the adsorption limit values. Desorption of the cations is possible by treatment with a stronger complexing agent such as ethylenediaminetetracetic acid.

Immobilization of residual dyes onto ion-exchanger cellulosic materials

This article reports on the preparation of cationized cotton fiber by treating alkali cellulose cotton fibers with epoxy propyltrimethylammonium chloride (EPTMAC) in a nonaqueous medium and its use as support for the immobilization of pollutant dyes. Evidence of attaching quaternary ammonium groups onto cellulose is provided by IR analysis, nitrogen determination, and weight uptake. Four EPTMAC-Cotton fiber samples with different nitrogen content (0.5-1.85) are tested for the adsorption of four acid dyes (Acid Blue 25, Acid Yellow 99, Reactive Yellow 23, and Acid Blue 74). Adsorption is followed spectrometrically, the capacity of adsorption depending on the nitrogen content and on the number of anionic groups in the dye. The Langmuir and Freundlich isotherms constants are evaluated from the experimental data, but better agreement is obtained by using a composite isotherm of the general form Y e = iC e /(1 + jC e m ), where i, j, and m are constants.

Adsorption of heavy metal ions on virgin and chemically-modified lignocellulosic materials

Amidoximated wood sawdust (Am-WS) and wood flour (Am-WF) were prepared using the same procedure as described recently for amidoximated cellulose (Am-Cell). The modified supports thus obtained were characterized by IR, TGA and DSC methods. In comparison to the untreated material, such treatment led to a considerable increase in adsorption capacity towards heavy metal ions from aqueous solution. The quantity adsorbed increased with pH, initial metal ion concentration and immersion time. The formation of a 1:1 complex between the amidoxime group and Cu(II), Cr(III) and Cd(II) ions and a 2:1 complex with the Ni(II) ion was demonstrated by the adsorption limit values. Overall, Am-WS and Am-WF exhibited similar behaviour to Am-Cell and are suitable for the treatment of wastewaters containing heavy metal ions.

The Use of Eucalyptus Barks for the Adsorption of Heavy Metal Ions and Dyes

Eucalyptus barks harvested in Lebanon were used for the adsorption of pollutants such as heavy metal ions and dyes. Washing with water or pretreatment with formaldehyde was performed on the bark powder. The adsorption capacity of this material towards CuII, CrIII, CdII and NiII was evaluated in a batch process for various parameters. The results obtained showed that the retention capacity increased with contact time, pH and initial metal ion concentration but decreased with temperature. The adsorption capacities were 2.61, 0.71, 2.24 and 0.75 mmol/g adsorbent for CuII, CrIII, CdII and NiII, respectively. Eucalyptus barks are also very efficient for the adsorption of dyes (Acid Blue 25, Erichrome Blue Black B and Calmagite) because of interaction between the hydroxy and amino groups of the dyes and the phenolic moities of bark. This adsorption was modified when metal ions had already been adsorbed on to the barks as a result of the formation of a 1:1 complex between the dye and the metal ion. Desorption was achieved by treating with the sodium salt of ethylenediamine-tetraacetic acid (EDTA) for metal ions and by heating at 75°C in aqueous medium for dyes. After desorption, the recycling of the support was tested for potential use as a means of concentrating pollutants.

The use of amidoximated cellulose for the removalof metal ions and dyes from waste waters

The adsorption of metal ions such as Cu(II), Cr(III), Cd(II) and Ni(II)and dyes such as Acid Blue 25, Calmagite and Eriochrome Blue Black Bis performed onto amidoximated cellulose (Am-Cell). Different ways are possible for theadsorption of these pollutants onto Am-Cell : adsorption of each pollutantaloneon the support, or cumulative adsorption of both metal ions and dyes on the samesupport. In the last case, the pollutants may be adsorbed simultaneously from aunique solution, or successively from two different solutions, whatever theorder. Am-Cell loaded or not with metal ions shows a high capacity for dyeadsorption. Ternary complexes involving metal/dye/amidoxime are formed. Theobserved stoichiometries are 1/1/1 with Cu(II), Cr(III) and Cd(II) ions and1/1/2with Ni(II) ion. A quasi-total and specific desorption of either metal ions (bytreatment with ethylenediaminetetracetic salt) or of dyes (by heating inaqueoussolution) is possible from these ternary complexes. Concerning the dyes, manysuccessive adsorption/desorption cycles are possible without a noticeablechange in the adsorption capacity.

Physicochemical modifications of partially esterified cellulose evidenced by inverse gas chromatography

Partial esterification of cellulose using acyl chlorides having 5 and 16 carbon atoms was performed in a swelling medium to produce cellulosic esters with two different degrees of substitution (DS = 0.15 and 0.45). The effects of this treatment on the surface energy, on the water uptake, and on the acido-basic character of the cellulose were studied by inverse gas chromatography and thermogravimetric analysis. The attaching of alkyl chains to the surface of cellulose reduces its acidic character and its hydrophilicity and the DS required for such an effect depends on the chain length.

Cationized Lignocelluloses as Scavengers for Anionic Surfactants. II. Hydrophobic Interactions

As reported in Part I of this study, anionic surfactants are rapidly adsorbed and strongly retained on cationized lignocellulosic materials as a result of ionic interactions. Consequently, the initially hydrophilic surface of the sorbent is strongly modified by the adsorbed surfactant molecules. Hydrophobic interactions with this modified surface allow a second layer of surfactant molecules to be adsorbed via their alkyl chains. Many combinations are possible with different kinds of surfactants, with the highest adsorption capacity being obtained when zwitterionic surfactants are involved in the second step.

Adsorption of Oleate Anions on to Cationized Lignocelluloses

Oleic acid and its salts are present among the toxic pollutants in olive oil mill wastewaters. Four lignocellulosic materials modified by grafting quaternary ammonium groups have been tested for the adsorption of the oleate anion from aqueous solutions, viz. cotton fibres, viscose fabric, wood sawdust and maize cob powder. As a result of their strong ionic interactions, the carboxylate moities were entrapped at a rate equivalent to the ammonium content of the support. Furthermore, when this charged support was left in contact with the polluted solution without agitation, an additional quantity of pollutant was adsorbed due to associations by the hydrophobic tails of the oleate moities. Partial desorption was achieved in 1 M HCl solution.