Removal of heavy metals (Co, Cr, and Zn) during calcium–aluminium–silicate–hydrate and trioctahedral smectite formation

• Published in: Journal of materials science Vol. 54; no. 13; pp. 9331 - 9351
• Main Authors: Baldermann, Andre, Landler, Andreas, Mittermayr, Florian, Letofsky-Papst, Ilse, Steindl, Florian, Galan, Isabel, Dietzel, Martin
• Format: Journal Article
• Language: English
• Published: New York Springer US 01-07-2019; Springer; Springer Nature B.V
• Subjects: Aluminosilicates; Aluminum; Calcium aluminum silicates; Calcium silicate hydrate; Cation exchanging; Characterization and Evaluation of Materials; Chemical composition; Chemical precipitation; Chemical Routes to Materials; Chemistry and Materials Science; Chromium; Classical Mechanics; Clay; Cobalt; Concrete structures; Crystallography and Scattering Methods; Gels; Hazardous waste management industry; Heavy metals; Hydrates; Immobilization; Interlayers; Materials Science; Mineralogy; Polymer Sciences; Precipitates; Precipitation (Meteorology); Radioactive waste disposal; Radioactive wastes; Silicates; Silicon; Smectite; Smectites; Sol-gel processes; Solid Mechanics; Underground structures; Waste management; Zinc
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-019-03541-5

Hydrated aluminosilicates were synthesized with and without aqueous heavy metals (Me), such as cobalt (Co), chromium (Cr), and zinc (Zn), by a sol–gel process at different initial molar ratios of Ca/(Si + Al) (0.6–1.6) and Me/Si (0.0–2.0), and constant Al/Si ratio (0.05) using equilibrium-approaching experiments. The chemical composition of the reactive solutions during aluminosilicate precipitation and maturation was monitored by ICP-OES. The mineralogy, nanostructure, and chemical composition of the precipitates were studied by XRD and high-resolution TEM. At Me/Si ratios ≤ 0.2, calcium–aluminium–silicate–hydrates (C–A–S–H) with a defect 14 Å tobermorite-like structure formed, whereas at a Me/Si ratio of 2.0, either trioctahedral Co- and Zn-smectite or amorphous Cr gels precipitated, independent of the initial Ca/(Si + Al) ratio used for gel synthesis. The immobilization capacities for
Co
2
+
,
Cr
3
+
, and
Zn
2
+
by C–A–S–H, Cr gel, and trioctahedral smectite are 3–40 mg/g, 30–152 mg/g, and 122–141 mg/g, respectively. The immobilization mechanism of heavy metals is based on a combination of isomorphous substitution, interlayer cation exchange, surface (ad)sorption, and surface precipitation. In engineered systems, such as underground concrete structures and nuclear waste disposal sites, hydrated aluminosilicates should exhibit a high detoxication potential for aqueous heavy metals.