Retention mechanisms for toxic cations using artificial confinement barriers of clay-cement mixtures
✍ Scribed by F. Delattre-Louvel; C. Lapeyre; R. Struillou; M. Arnould
- Book ID
- 103074041
- Publisher
- Elsevier Science
- Year
- 1993
- Tongue
- English
- Weight
- 494 KB
- Volume
- 34
- Category
- Article
- ISSN
- 0013-7952
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✦ Synopsis
Artificial linings for the confinement of toxic wastes are often made of clay-cement mixtures, which sometimes contain other powdery substances, such as carbonates. These mixtures are characterized by: (1) high alkaline contents; and (2) strong adsorption capacities, due to the high specific surface of the clay and the artificial silico-aluminous components.
The migration of toxic cations normally occurs in acidic solutions. When they come in contact with the clay-cement mixture, the alkaline content of these solutions is progressively activated. The reactions which occur are related to the acid-base neutralization reaction.
The sorption of Pb 2 ÷ on a clay-cement mixture was studied using the batch equilibrium technique and percolation tests. The change in the retention capacity with increasing pH and the amount of Pb 2 + added is similar in both cases. Pb 2 + is entirely retained at pH > 7 and this can be attributed to precipitation as hydroxides or hydroxycarbonates. When the alkaline content of the mixture is neutralized, the pH of the solution lowers progressively and the clay-cement mixtures, especially the cement-rich mixture, exhibited stoichiometric uptake of Pb 2 + and release of Ca 2 +, suggesting the formation of lead silicate.