Uptake of aqueous heavy metal ions (Co2+, Cu2+ and Zn2+) by calcium-aluminium-silicate-hydrate gels

Andre Baldermann*, Veronika Preissegger, Sanja Šimić, Ilse Letofsky-Papst, Florian Mittermayr, Martin Dietzel

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Calcium-aluminium-silicate-hydrate (C-A-S-H) gels containing heavy metal ions (Me: Co2+, Cu2+ or Zn2+) were precipitated at different Me/Si molar ratios to study the uptake mechanism and immobilization capacity. Aqueous solution chemistry and solid-phase characterization using XRD, FTIR, ESEM-EDX, TEM-HAADF and TG-DSC methods reveal threshold values for ion substitution of ~55–60 mol% for Zn, ~30–40 mol% for Co and ~25–30 mol% for Cu in defective tobermorite-type C-A-S-H with (Ca + Me)/(Si + Al) molar ratios from 0.86 to 1.04. At higher aqueous Me concentrations, Me (chloride) hydroxides start to co-precipitate. The uptake mechanism of Me ions by C-A-S-H is based on (i) isomorphous substitution of Me for Ca in the CaO layer, (ii) ion exchange in the interlayer, (iii) tetrahedral substitution (Zn) within the dreierketten chains and (iv) surface adsorption onto the C-A-S-H gel structure. Systematics in crystal-chemistry of Me-bearing C-A-S-H and implications for application and performance in natural and man-made settings are discussed.

Original languageEnglish
Article number106521
JournalCement and Concrete Research
Publication statusPublished - Sept 2021


  • C-A-S-H phase
  • Environment
  • Heavy metals, crystal chemistry
  • Pollution

ASJC Scopus subject areas

  • Building and Construction
  • Materials Science(all)


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