Interaction between ammonium smectite and some simple organic molecules : pollution prediction in waste landfill
Résumé
Nowadays the majority of wastes is going to landfill sites but waste decomposition produces high amount of pollutants. Because of their interesting properties (low permeability after compaction, expansion ability and high Cation Exchange Capacity) smectites are usually used as pollutant barriers at the bottom of waste landfill. Landfill leachates are mainly characterized by large amounts of ammonium, which may exchanged with the cations of clay barriers. To better understand the behaviour of these barriers in the presence of leachates, the study of SWy-2 montmorillonite exchanged with ammonium cations in interaction with different simple molecules produced by waste degradation is proposed. Selected molecules are characteristic of a functional group: ethanol (alcohol), acetone (cetone), formamide (amide), acetonitrile (nitrile), MTBE (ether), benzene (aromatic hydrocarbon), phenol (phenol), aniline (amine) and dichloromethane (aliphatic hydrocarbon). Batch experiments were performed during 7 days at several molecular concentrations higher than in landfill. Treated samples were then dried at 40°C and analysed by Fourier-Transform Infrared spectroscopy, X-Ray powder diffraction, thermogravimetry, ICP-OES and LECO (for C and N contents). The sorption capacity considerably varies according to molecules. Some molecules (benzene, acetonitrile, MTBE...) do not show fixation, or only a very weak adsorption. Others (aniline, formamide...) are adsorbed. For instance, the sample which interacted with aniline shows a basal distance increase from 1.19 nm (NH4-SWy-2) to 1.50 nm and a sharpening of the (001) reflexion. This interlayer space reorganization is attributed to the fixation of aniline molecules on the hydrated interlayer cation (ammonium in this study). The behaviour of NH4-SWy-2 sample in the presence of formamide is quite different. The formamide molecules take the place of interlayer water molecules in the vicinity of ammonium cation which increases the swelling properties of the clay sample. Some consequences on clay barrier modifications can then be discussed.