Water-based fractionation of a commercial humic acid. Solid-state and colloidal characterization of the solubility fractions

Weronika M. Swiech, Ian Hamerton, Huang Zeng, David J. Watson, Eleanore Mason, Spencer E. Taylor*

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

10 Citations (Scopus)
287 Downloads (Pure)


Background and hypothesis: Humic acid (HA) is of considerable environmental significance, being a major component of soil, as well as being considered for application in other technological areas. However, its structure and colloidal properties continue to be the subject of debate, largely owing to its molecular complexity and association with other humic substances and mineral matter. As a class, HA is considered to comprise supramolecular assemblies of heterogeneous species, and herein we consider a simple route for the separation of some HA sub-fractions.
Experiments: A commercial HA sample from Sigma-Aldrich has been fractionated into two soluble (S1, S2) and two insoluble (I1, I2) fractions by successive dissolution in deionized water at near-neutral pH. These sub-fractions have been characterized by solution and solid-state approaches.
Findings: Using this simple approach, the HA has been shown to contain non-covalently bonded species with different polarity and water solubility. The soluble and insoluble fractions have very different chemical structures, as revealed particularly by their solid-state properties (13C NMR and IR spectroscopy, and TGA); in particular, S1 and S2 are characterized by higher carbonyl and aromatic contents, compared with I1 and I2. As shown by solution SAXS measurements and AFM, the soluble fractions behave as hydrophilic colloidal aggregates of at least 50 nm diameter.
Original languageEnglish
Pages (from-to)28-38
Number of pages11
JournalJournal of Colloid and Interface Science
Early online date12 Aug 2017
Publication statusPublished - 15 Dec 2017


  • AFM
  • Colloidal properties
  • Humic acid fractionation
  • IR spectroscopy
  • Solid-state NMR
  • Surface tension
  • SAXS
  • TGA
  • Zeta potential


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