Speciation of heavy metal ions as influenced by interactions with montmorillonite, Al hydroxide polymers and citrate

R.P.T. Janssen

Research output: Thesisinternal PhD, WU


<p>Clay minerals, metal-hydroxides and organic matter can bind metal ions; moreover they also interact with each other. These mutual interactions influence the metal binding to a significant extent. In this study, the speciation of the heavy metal ions Zn and Ph was investigated in model systems consisting of various combinations of the clay mineral montmorillonite (Na saturated), Al hydroxide polymers and citric acid at pH 5.0, 6.0 and 6.6. A speciation model was developed to determine the distribution of Zn and Pb in these systems. pH had a pronounced effect on Zn and Pb binding. Zn and Pb binding to the clay/Al hydroxide polymer systems decreased with decreasing pH. The decrease of the pH led to a decrease of the cation exchange capacity and to a decrease of the affinity of the Al hydroxide polymers for metal ions. The decrease in metal ion binding was also influenced by increasing competition of Al <sup><font size="-2">3+</font></SUP>. The effect of the Al:clay ratio on metal binding was influenced by the pH. This is because the nature of the Al hydroxide is dependent on the Al:clay ratio at pH 5.0 and independent at pH 6.6. The available binding sites on the Al hydroxide polymers have a high affinity for Zn and Pb ions. Zn and Pb binding on the siloxane surface became relatively more important when the binding sites on the Al hydroxide polymers were nearly all occupied. Citrate sorption to clay/Al hydroxide polymer systems was strongly dependent on the conditions of formation of the systems. Citrate adsorbed to the edge faces of the clay platelets of aged clay/Al hydroxide systems. When citrate is present during the formation of clay/Al hydroxide systems, it was found that citrate was incorporated in the Al hydroxide polymers. At increased citrate:Al ratios, citric acid can perturb the formation or dissolve the Al hydroxide polymers. The distribution of Zn over the various species in a clay/Al hydroxide polymer/citrate system was calculated by using the speciation model. Only slightly less Zn was sorbed to the Al hydroxide polymers compared to the same systems without citrate. For high molar fractions of Zn bound to the exchange sites, binding of Zn to the Al hydroxide increased strongly in the presence of citrate, suggesting the formation of a coprecipitate or solid solution between Al- and Zn hydroxide and citrate. At increasing citrate:Al ratios, Zn sorption decreased strongly, due to Zn and Al complexation by citrate.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • van Riemsdijk, W.H., Promotor
  • Bruggenwert, M.G.M., Promotor, External person
Award date16 Jun 1995
Place of PublicationS.l.
Print ISBNs9789054853992
Publication statusPublished - 1995


  • soil
  • heavy metals
  • absorption
  • adsorption
  • clay minerals
  • chemical speciation
  • metal ions
  • montmorillonite
  • aluminium hydroxide
  • polymers
  • citric acid

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