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Retention mechanisms for toxic cations using artificial confinement barriers of clay-cement mixtures
Abstract 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 Pb2+ 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 Pb2+ added is similar in both cases. Pb2+ 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 Pb2+ and release of Ca2+, suggesting the formation of lead silicate.
Retention mechanisms for toxic cations using artificial confinement barriers of clay-cement mixtures
Abstract 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 Pb2+ 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 Pb2+ added is similar in both cases. Pb2+ 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 Pb2+ and release of Ca2+, suggesting the formation of lead silicate.
Retention mechanisms for toxic cations using artificial confinement barriers of clay-cement mixtures
Delattre-Louvel, F. (author) / Lapeyre, C. (author) / Struillou, R. (author) / Arnould, M. (author)
Engineering Geology ; 34 ; 151-158
1993-01-14
8 pages
Article (Journal)
Electronic Resource
English
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