Physico-Chemical Characterization of Modified Tunisian Kaolin by Phosphoric Acid

Аннотация

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 H₃PO₄ (28 and 54 wt % P₂O₅), 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, ²⁹Si and ³¹P 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 % P₂O₅ and after 4 h with phosphoric acid 54 wt % P₂O₅. Hereafter, the forming of an amorphous silica phase is detected, whose confirmation is effected by the ²⁹Si NMR analysis. FTIR studies indicate that acid treatment under reflux conditions leads to the removal of the octahedral Al³⁺ cations for the two types of phosphoric acid. In fact, the chemical analysis shows that the leaching of Al³⁺ ions increases progressively with severity and the time of the reaction. The acid treatment with H₃PO₄ 54 wt % P₂O₅ at 90°C, enlarged the surface area from 24 to 150 m²/g. Thus, the solids obtained by the acid treatments can be used as promising adsorbents and catalyst supports.