Research paper
Adsorption by goethite (α-FeOOH) of humic substances from three different lakes

https://doi.org/10.1016/0009-2541(81)90086-3Get rights and content

Abstract

The adsorption to a sample of goethite of humic substances from three different lakes has been studied. The humics differ with respect to molecular weight and content of ionisable groups. Each humic preparation shows essentially the same dependence of adsorption on pH, and adsorption isotherms determined in 0.01 M NaCl in equilibrium with air at pH 7 obey the Langmuir equation. The adsorption capacity [(weight of humics adsorbed)/(weight of goethite), at saturation] increases with increasing humic molecular weight and decreases with increasing extent of ionisation (charges per gram of humics at pH 7). However, if the adsorption capacity is expressed in molar units (i.e. mol humics per gram of goethite) the values for the three preparations are similar and bear no relationship to either molecular weight or charge. Adsorption capacities are too large to be consistent with the humic molecules being adsorbed as close-packed spheres. The free energies of adsorption of the three preparations are approximately equal.

On the basis of data reported for the adsorption of small molecules to goethite, it is inferred that humic adsorption takes place by the interaction with the oxide surface of a fraction of the humic carboxyl groups. The similar free energies of adsorption suggest that the actual number of carboxyl groups involved in the interaction is about the same for each humic preparation. The part of the humic molecule not involved in adsorption probably extends away from the surface towards or into the bulk solution.

References (22)

  • R.F.C. Mantoura et al.

    The analytical concentration of humic substances from natural waters

    Anal. Chim. Acta

    (1975)
  • E. Tipping

    The adsorption of aquatic humic substances by iron oxides

    Geochim. Cosmochim. Acta

    (1981)
  • R.J. Atkinson et al.

    Adsorption of potential-determining ions at the ferric oxide-aqueous electrolyte interface

    J. Phys. Chem.

    (1967)
  • R.J. Atkinson et al.

    Infra-red study of phosphate adsorption on goethite

    J. Chem. Soc., Faraday Trans I

    (1974)
  • L.T. Evans et al.

    The adsorption of humic and fulvic acids by clays

    J. Soil Sci.

    (1959)
  • W. Flaig et al.

    Chemical composition and physical properties of humic substances

  • E.T. Gjessing

    Physical and Chemical Characteristics of Aquatic Humus

  • D.J. Greenland

    Interaction between clays and organic compounds in soils, I. Mechanisms of interaction between clays and defined organic compounds

    Soils Fert.

    (1965)
  • D.J. Greenland

    Interaction between clays and organic compounds in soils, II. Adsorption of soil organic compounds and its effect on soil properties

    Soils Fert.

    (1965)
  • F.J. Hingston et al.

    Specific adsorption of anions on goethite

  • T.A. Jackson

    Humic matter in natural waters and sediments

    Soil Sci.

    (1975)
  • Cited by (98)

    • Iron-mediated mineralogical control of organic matter accumulation in tropical soils

      2017, Geoderma
      Citation Excerpt :

      The C:Fe values > 1 observed for PP fractions suggests the liberation of low-density organic-dominated structures, in addition to lower C:Fe monolayer structures. The low C:Fe values of < 1 for observed in HH and DH fractions indicate that surficial reactions dominate (Fig. 5), although the C:Fe ratios of the OM sorbed on FeDH were lower than those observed involving SRO Fe phases and dispersable/chelated Fe (Kaiser and Zech, 1997; Tipping, 1981). Because DOCHH and DOCDH only represent small fractions of total soil C, we suggest that simple surface adsorption to SRO and pedogenic Fe phases is a minor mechanism of total soil C accumulation in these soils.

    • Specific ion effect on the point of zero charge of α-alumina and on the adsorption of 3,4-dihydroxybenzoic acid onto α-alumina surface

      2014, Colloids and Surfaces A: Physicochemical and Engineering Aspects
      Citation Excerpt :

      Nevertheless, a similar reversibility in specific ion effects series in pH of buffer solution is reported and at the interface (glass/water) and the modulation of water structure at the interface is responsible for the reversibility of specific ion effects series [51]. We suggest that the polarizability of ions is not the primary parameter for the specific ion effects sequence but most probably the different solvation environments or more specifically the magnitude of surface hydration below and above the PZC in conjunction with different interactions (ion-surface potentials, ion-solvent, hydrophobic interactions, ion-surface, dispersion force) are the governing factors for the specific ion effect and its reversibility [13,30,49,51–53]. For understanding this aspect both theoretical and experimental justifications have appeared in the literatures [12,13,30,31,34,50,54–57] but still needs details examination of a system of interest.

    View all citing articles on Scopus

    This work was supported by the Natural Environment Research Council.

    View full text