The role of variable surface charge and surface complexation in the adsorption of humic acid on magnetite

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Abstract

The ionic strength dependence of humic acid (HA) adsorption on magnetite (Fe3O4) was investigated at pH ∼5, ∼8 and ∼9, where variable charged magnetite is positive, neutral and negative, respectively. The adsorption studies revealed that HA has high affinity to magnetite surface especially at lower pH, where interacting partners have opposite charges. However, in spite of electrostatic repulsion at pH ∼9 notable amounts of humate are adsorbed. Increasing ionic strength enhances HA adsorption at each pH due to charge screening. The dominant interaction is probably a ligand-exchange reaction, nevertheless the Coulombic contribution to the organic matter accumulation on oxide surface is also significant under acidic condition. The results from size exclusion chromatography demonstrate that the smaller size HA fractions enriched with functional groups are adsorbed preferentially on the surface of magnetite at pH ∼8 in dilute NaCl solution.

Original languageEnglish
Pages (from-to)99-109
Number of pages11
JournalColloids and Surfaces A: Physicochemical and Engineering Aspects
Volume230
Issue number1-3
DOIs
Publication statusPublished - Dec 10 2003

Keywords

  • Humic acid
  • Iron oxide
  • Magnetite
  • Size fractionation
  • Surface complexation

ASJC Scopus subject areas

  • Surfaces and Interfaces
  • Physical and Theoretical Chemistry
  • Colloid and Surface Chemistry

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