TY - JOUR

T1 - Organic cation exchanged montmorillonite and vermiculite as adsorbents for Cr(VI)

T2 - Effect of layer charge on adsorption properties

AU - Dultz, Stefan

AU - An, Jong Hyok

AU - Riebe, Beate

N1 - Funding information: The work was supported by the Federal Ministry for Economic Affairs and Employment (BMWA) under contract number 02E9481 and the Gottlieb Daimler- and Karl Benz-Foundation through their fellowship program (J.-H. An).

PY - 2012/10

Y1 - 2012/10

N2 - The binding of anions at interlayer sites of organo-clay minerals is supposed to be stronger and more specific than on the external surfaces. In this study the Cr(VI) adsorption properties of two hydrous phyllosilicates, a montmorillonite and a vermiculite modified with Hexadecylpyridinium (HDPy), Hexadecyltrimethylammonium (HDTMA) and Benzethonium (BE) were investigated at pH 3-9. Structural features were determined by X-ray diffraction. The surface charge of the organo-clays at different pH was analyzed by polyelectrolyte titration in the cell of a particle charge detector. The effect of competing anions Cl-, NO3- and SO42- on Cr(VI) adsorption was determined. The interlayer space structures of the organo-vermiculites were paraffin-type, whereas it was pseudotrimolecular for the organo-montmorillonites. Besides organic cations also considerable amounts of inorganic cations were present in the interlayer space. As a consequence of organic cation treatment the surface charge of the clays shifted from negative to positive values up to 269mmolckg-1; it was highly affected by the specific surface area, layer charge and pH. Depending on the kind of organic cation, organo-vermiculites and -bentonites showed comparable adsorption capacity for Cr(VI), which was at pH 4.5 0.38 and 0.30molkg-1 for HDPy- and HDTMA-vermiculites, respectively and 0.37 and 0.26molkg-1 for the corresponding bentonites. For all organo-clays the adsorbed amount of Cr(VI) decreased with increasing pH. The effect of competing anions, Cl-, NO3- and SO42- on Cr(VI) adsorption appeared to be small. For organo-vermiculites a higher portion of anion adsorption sites was located in the interlayer space. In context with the high share of adsorption sites in the interlayer space it is suggested that both organo-vermiculites and organo-bentonites are promising adsorbents of Cr(VI) in water purification methods.

AB - The binding of anions at interlayer sites of organo-clay minerals is supposed to be stronger and more specific than on the external surfaces. In this study the Cr(VI) adsorption properties of two hydrous phyllosilicates, a montmorillonite and a vermiculite modified with Hexadecylpyridinium (HDPy), Hexadecyltrimethylammonium (HDTMA) and Benzethonium (BE) were investigated at pH 3-9. Structural features were determined by X-ray diffraction. The surface charge of the organo-clays at different pH was analyzed by polyelectrolyte titration in the cell of a particle charge detector. The effect of competing anions Cl-, NO3- and SO42- on Cr(VI) adsorption was determined. The interlayer space structures of the organo-vermiculites were paraffin-type, whereas it was pseudotrimolecular for the organo-montmorillonites. Besides organic cations also considerable amounts of inorganic cations were present in the interlayer space. As a consequence of organic cation treatment the surface charge of the clays shifted from negative to positive values up to 269mmolckg-1; it was highly affected by the specific surface area, layer charge and pH. Depending on the kind of organic cation, organo-vermiculites and -bentonites showed comparable adsorption capacity for Cr(VI), which was at pH 4.5 0.38 and 0.30molkg-1 for HDPy- and HDTMA-vermiculites, respectively and 0.37 and 0.26molkg-1 for the corresponding bentonites. For all organo-clays the adsorbed amount of Cr(VI) decreased with increasing pH. The effect of competing anions, Cl-, NO3- and SO42- on Cr(VI) adsorption appeared to be small. For organo-vermiculites a higher portion of anion adsorption sites was located in the interlayer space. In context with the high share of adsorption sites in the interlayer space it is suggested that both organo-vermiculites and organo-bentonites are promising adsorbents of Cr(VI) in water purification methods.

KW - Anion exchange

KW - Cr(VI)

KW - Layer charge

KW - Organo-clay minerals

KW - Selectivity

UR - http://www.scopus.com/inward/record.url?scp=84869163876&partnerID=8YFLogxK

U2 - 10.1016/j.clay.2012.05.004

DO - 10.1016/j.clay.2012.05.004

M3 - Article

AN - SCOPUS:84869163876

VL - 67-68

SP - 125

EP - 133

JO - Applied clay science

JF - Applied clay science

SN - 0169-1317

ER -