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, 3M, 5M and 10 M at 110 degrees C for 4 h followed by calcination at 500 degrees C for 2 h. The physico-chemical characteristics of acid-leached kaolinite clay were studied by XRF, XRD, FTIR,TGA, DTA, SEM and N-2 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 10M 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 m(2)/g to 143 m(2)/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. (C) 2010 Elsevier B.V. All rights reserved.