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Uptake of aqueous heavy metal ions (Co2+, Cu2+ and Zn2+) by calcium-aluminium-silicate-hydrate gels
Abstract 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.
Highlights C-A-S-H gels containing metal ions (Co2+, Cu2+ or Zn2+) were precipitated by a sol-gel technique. Uptake mechanism and immobilization capacity of divalent metal ions by C-A-S-H are elucidated. Up to ~55–60 mol% of Zn can be incorporated in defective tobermorite-type C-A-S-H. Metal uptake by C-A-S-H is controlled mainly by isomorphous substitution for Ca ions. Crystal-chemical features of C-A-S-H gels and implications for practical application are discussed.
Uptake of aqueous heavy metal ions (Co2+, Cu2+ and Zn2+) by calcium-aluminium-silicate-hydrate gels
Abstract 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.
Highlights C-A-S-H gels containing metal ions (Co2+, Cu2+ or Zn2+) were precipitated by a sol-gel technique. Uptake mechanism and immobilization capacity of divalent metal ions by C-A-S-H are elucidated. Up to ~55–60 mol% of Zn can be incorporated in defective tobermorite-type C-A-S-H. Metal uptake by C-A-S-H is controlled mainly by isomorphous substitution for Ca ions. Crystal-chemical features of C-A-S-H gels and implications for practical application are discussed.
Uptake of aqueous heavy metal ions (Co2+, Cu2+ and Zn2+) by calcium-aluminium-silicate-hydrate gels
Baldermann, Andre (author) / Preissegger, Veronika (author) / Šimić, Sanja (author) / Letofsky-Papst, Ilse (author) / Mittermayr, Florian (author) / Dietzel, Martin (author)
2021-06-15
Article (Journal)
Electronic Resource
English
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