Physico-Chemical Characterization of Modified Tunisian Kaolin by Phosphoric Acid

In this study, crude Tunisian kaolin clay (from the Tabarka region—North of Tunisia) was subjected to refluxing with phosphoric acid under different operating conditions. Acid activation was carried out with H 3 PO 4 (28 and 54 wt % P 2 O 5 ), at temperatures of 60 and 90°C, with the time of treatment ranging from 2 to 12 h. The structure of acid leached kaolinite clay was characterized by; the XRD, FTIR, SEM, 29 Si and 31 P NMR techniques and the Brunauer Emmett Teller theory was uses as the base for respective calculations. The chemical composition was determined by ICP. The results of XRD show that the kaolin acid treatment at 90°C provoked a destruction of clay structure after 6 h with phosphoric acid 28 wt % P 2 O 5 and after 4 h with phosphoric acid 54 wt % P 2 O 5 . Hereafter, the forming of an amorphous silica phase is detected, whose confirmation is effected by the 29 Si NMR analysis. FTIR studies indicate that acid treatment under reflux conditions leads to the removal of the octahedral Al 3+ cations for the two types of phosphoric acid. In fact, the chemical analysis shows that the leaching of Al 3+ ions increases progressively with severity and the time of the reaction. The acid treatment with H 3 PO 4 54 wt % P 2 O 5 at 90°C, enlarged the surface area from 24 to 150 m 2 /g. Thus, the solids obtained by the acid treatments can be used as promising adsorbents and catalyst supports.