TY - JOUR
T1 - Uptake of aqueous heavy metal ions (Co2+, Cu2+ and Zn2+) by calcium-aluminium-silicate-hydrate gels
AU - Baldermann, Andre
AU - Preissegger, Veronika
AU - Šimić, Sanja
AU - Letofsky-Papst, Ilse
AU - Mittermayr, Florian
AU - Dietzel, Martin
PY - 2021/9
Y1 - 2021/9
N2 - 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.
AB - 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.
KW - C-A-S-H phase
KW - Environment
KW - Heavy metals, crystal chemistry
KW - Pollution
UR - http://www.scopus.com/inward/record.url?scp=85108262267&partnerID=8YFLogxK
U2 - 10.1016/j.cemconres.2021.106521
DO - 10.1016/j.cemconres.2021.106521
M3 - Article
AN - SCOPUS:85108262267
SN - 0008-8846
VL - 147
JO - Cement and Concrete Research
JF - Cement and Concrete Research
M1 - 106521
ER -