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@PHDTHESIS{Khalaf:33181,
      author       = {Khalaf, Moustafa},
      title        = {{E}ffect of the fractionation and immobilization on the
                      sorption properties of humic acid},
      volume       = {4046},
      issn         = {0944-2952},
      school       = {Techn. Hochsch. Aachen},
      type         = {Dr. (FH)},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {PreJuSER-33181, Juel-4046},
      series       = {Berichte des Forschungszentrums Jülich},
      pages        = {114 p.},
      year         = {2003},
      note         = {Record converted from VDB: 12.11.2012; Aachen, Techn.
                      Hochsch., Diss., 2003},
      abstract     = {Humic substances modify the surface of inorganic soil
                      constituents changing the nature and amount of adsorption
                      sites for contaminants and also influencing the
                      particle-particle interactions and thus the mobility and
                      transport behavior of the soil particles. The aim of this
                      PhD work was to investigate the effects of the interactions
                      between two important soil components, aluminum oxide and
                      humic acid, on the sorption behavior of 2,4-dichlorophenol
                      under laboratory conditions selected to model the soil
                      systems. Humic acid is very heterogeneous in terms of
                      physical and chemical properties. To reduce the chemical
                      heterogeneity of the extracted humic acid (from the A$_{p}$
                      horizon of the Orthic Luvisol, Merzenhausen, Germany), a
                      fractionation scheme using the ultrafiltration technique was
                      used to obtain eight size fractions of the humic acid. The
                      extracted humic acid and its fractions were characterized by
                      potentiometric acid-base titration, elemental analysis and
                      different spectroscopic methods (NMR, UV-VIS and FT-IR
                      spectroscopy). Clear chemical differences between the humic
                      acid size fractions were observed. Smaller size fractions of
                      the soil humic acid contained more chargeable functional
                      groups and larger percentage of aromatic carbon than the
                      larger size fractions. Conversely, the percentage of
                      aliphatic carbon increased with increasing apparent
                      molecular weight. Moreover, the solid-state $^{19}$F-NMR was
                      used to study the sorptive uptake of hexafluorobenzene by
                      the humic acid and its fractions. It was found that humic
                      acid molecules have different chemical environments into
                      which organic pollutant such as hexafluorobenzene can sorb.
                      Small humic acid molecules have at least three sorption
                      sites (“rigid”, “soft” and other new domains) that
                      are more clearly defined and homogeneous than the sorption
                      domains found in larger humic acid molecules. The effect of
                      the pH and the electrolyte concentration on the adsorption
                      of the humic acid onto alumina surfaces as well as on the
                      colloidal stability of these systems were studied. To better
                      understand the binding mechanisms these results were also
                      compared to those of polyacrylic acid. The adsorption of
                      humic acid or polyacrylic acid to alumina varied with pH and
                      electrolyte concentration, suggesting that the conformation
                      of the humic acid or polyacrylic acid in solution
                      significantly determines their structures on the mineral
                      surface. At low pH (< point of zero charge (PZC) of
                      alumina), increasing amounts of humic acid or polyacrylic
                      acid are adsorbed on the alumina surface with increasing
                      concentrations of solutes, resulting in a charge reversal
                      from positive to negative net total particle charge whilst
                      at high pH (> PZC), the electrophoretic mobility was shifted
                      to more negative values. The colloidal stability of the
                      alumina dispersions containing increasing amounts of the
                      added humic acid and polyacrylic acid, respectively, was
                      monitored using the dynamic light scattering technique. The
                      maximum aggregate size was observed around the zero
                      electrophoretic mobility, indicating the importance of the
                      charge neutralization mechanism. By comparing the adsorption
                      of the humic acid fractions on alumina surfaces, it was
                      found that the adsorbed amount increases with increasing
                      humic acid molecular size. Furthermore, an increase in the
                      rise of the adsorption isotherm in the plateau regions by
                      increasing the humic acid fraction size was also observed
                      which indicates a higher contribution of the hydrophobic
                      interactions due to the increase in the aliphatic carbon and
                      the decrease in the chargeable groups. The sorption results
                      of 2,4-dichlorophenol on the immobilized humic acid at
                      different pH and salt concentrations revealed that the value
                      of the sorption coefficient decreases as the ionic strength
                      decreases or the pH value increases which gives direct
                      evidence for the importance of the conformation of the
                      immobilized HA. These sorption isotherms can be described as
                      a linear isotherm, which indicates that the sorption of
                      2,4-dichlorophenol is predominantly a partitioning process
                      between the aqueous phase and the immobilized humic acid.},
      cin          = {ICG-IV},
      cid          = {I:(DE-Juel1)VDB50},
      pnm          = {Chemie und Dynamik der Geo-Biosphäre},
      pid          = {G:(DE-Juel1)FUEK257},
      typ          = {PUB:(DE-HGF)11 / PUB:(DE-HGF)3},
      url          = {https://juser.fz-juelich.de/record/33181},
}