Physicochemical and Geotechnical Evaluation of Stability of Natural Smectite/Kaolinite Soils as Geological Discharge Site of Acidic Solid Waste in Tunisia

This study aims to investigate the effects of acidic phosphate solution (PS) from phosphogypsum collected from the Tunisian Chemical Group in Gabes, with a pH of 2.6, on the physico-chemical and mechanical properties of Tunisian clay soils, Aleg (AG) and El Haria (EH). Here, the feasibility of employing these soils as natural impermeable barriers for phosphogypsum (PG) disposal sites has been explored. Mineralogical and chemical compositions of raw and modified clays were identified using XRD and XRF. The contact effect of phosphoric aqueous waste in comparison to tap water on raw clays, was revealed by a clear disappearance of the carbonate peak. The drained shear strength of Aleg soil decreased to 48 kPa. Conversely, the cohesion of El Haria soil increased with phosphate solution. Triaxial test results showed c’ and φ’ decreased to 44 kPa and 21° for AG and increased to 155 kPa and 27° for EH. AG and EH clays showed an important support capacity that reached 38 m and 57 m, respectively.