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- Title
Stabilization/Solidification of Wastes Containing Oxyanionic Metals: Reactions of Alkali-Activated Aluminosilicate Binders with Chromium, Arsenic, and Antimony in Comparison with Zinc.
- Authors
El-Eswed, Bassam; Dawoud, Jamal N.; Mahmoud, Wadah F.; Abu Salha, Yousef
- Abstract
During the last decade, alkali-activated aluminosilicates (fly ash, metakaolin, or blast furnace slag) or geopolymers have been investigated for their ability to immobilize wastes containing highly soluble oxyanionic metals of chromium (Cr), arsenic (As), and antimony (Sb). Effective stabilization of these metal anions was perceived as a challenging issue since they are not liable for precipitation or balancing the negatively charged Al tetrahedra of geopolymer. Moreover, the question about the possibility of covalent bonding of these metals to the geopolymeric aluminosilicate framework was never settled down. In the first part of the present work, the condensation reactions of oxyanionic Cr, As, and Sb species with Si were investigated using density-functional theory (B3LYP) in comparison with the reaction of Zn (cationic heavy metal) with Si and taking the reaction between Al and Si as the basic geopolymerization reaction. These calculations showed that the reaction of Si with Zn and Al species is much more favored (ΔG = − 67.107 and − 179.728 kJ/mol, respectively) than that of Si with Cr, As, and Sb species (ΔG = − 6.452, − 3.456, − 8.581 kJ/mol, respectively). For experimental verification of these results, reaction products of 30 wt% of metal salts (K2Cr2O7, K2CrO4, NaAsO2, and ZnCl2) and alkali-activated metakaolin were investigated using FTIR, XRD, and SEM techniques. The results indicated that all these salts did not affect geopolymerization characters, while ZnCl2 did. It can be concluded that wastes containing oxyanionic metals may represent a threat to our environmental even after their immobilization in geopolymer since they do not exhibit chemical bonding. However, the theoretical calculations showed that the highly alkaline or Na+-rich medium used in geopolymer preparation, which is usually thought to induce dissolution of aluminosilicate source, facilitates condensation reaction of silicate with aluminate, chromate, and arsenite species.
- Publication
Water, Air & Soil Pollution, 2022, Vol 233, Issue 9, p1
- ISSN
0049-6979
- Publication type
Article
- DOI
10.1007/s11270-022-05845-w