Monolith Hydroxysodalite from Low Grade Kaolin and its Application as an Adsorbent for Lead

Abstract

Low grade kaolin is converted to monolith hydroxysodalite dihydrate by hydrothermal treatment with 10M NaOH solution i.e., higher Na concentration, Na/Si =1.3. The X-ray diffraction and infrared methods are used to determine the chemical formula of cured material which is Na8Al6Si6O24(OH)2.2H2O. The CEC values do not correlate with that of SSA values, where for uncured kaolin the CEC have increased from 6.52 to 89.13 meq/100g for the cured kaolin or synthetic hydroxysodalite; on the other hand, the SSA values have decreased from 87 to 10 m2/g. An adsorption experiment shows that the expansion of the framework of hydroxysodalite is due to the replacement of Na+ by Pb2+; moreover, about 91% of Pb is effectively removed. To get optimum removal, the solution must be buffered to about pH=4.5.