Clayey soils are essential materials used to reduce hydraulic conductivity and pollutant migration, common at sites of waste disposal. This study investigates the possible use of a Tunisian soil as a lining material for disposal sites for acidic-fluoride wastes. A permeability test on a waste-solution sample (pH = 2.7) obtained from a disposal site in southern Tunisia was conducted over a period of about 2 years. The test results show that the permeability decreased with time until stabilized at 8.33×10−11 m/s. After the permeability test, the samples retrieved from the permeameter show a degradation state which varied with the thickness of the specimen. These samples can be classified into three zones (Z1: unaffected, Z2: moderately affected; and Z3: extensively affected). Physicochemical characterization of the three samples (Z1, Z2, and Z3), and of the original argillaceous soil, was by X-ray diffraction, Fourier transform infrared spectroscopy, differential thermal and thermal gravimetric analysis, 29Si and 27Al nuclear magnetic resonance, and N2-adsorption techniques. The original sample consists essentially of palygorskite, kaolinite, and quartz. Sample Z3 underwent complete dissolution of kaolinite which supports the precipitation of fluoroaluminate and the appearance of an X-ray amorphous silica phase. In samples Z1 and Z2, the soil adsorbs fluoride at a rate of ~68.5 mg/g and is highly resistant to acidic attack.