Effect of sulphuric acid treatment on the physico-chemical characteristics of kaolin clay

Natural kaolin was refluxed with sulphuric acid of different concentrations 1 M, 3 M, 5 M and 10 M at 110 °C for 4 h followed by calcination at 500 °C for 2 h. The physico-chemical characteristics of acid-leached kaolinite clay were studied by XRF, XRD, FTIR, TGA, DTA, SEM and N2 adsorption techniques. XRF and FTIR studies indicate that acid treatment under reflux conditions leads to the removal of the octahedral Al3+ cations along with other impurities. XRD of 5 M and 10 M treated kaolin shows that treatment with high concentrated acid provoked an amorphization resulting in the formation of an amorphous silica type phase. Leaching of Al3+ ions increased progressively with severity of the acid treatment. The acid treatment increased the Si/Al ratio from 0.65 to 8.09, surface area from 23 m2/g to 143 m2/g and pore volume from 0.361 cc/g to 1.18 cc/g as the acid concentration was increased to 10 M. Solids thus obtained by acid treatments can be used as promising adsorbents and catalyst supports.