Fixation of Heavy Metals in Clay and Sludge under Elevated Temperatures and Pressures

Abstract

Abstract The retention of heavy metal by clay minerals has been thoroughly studied. The smectic types, in particular montmorilkmite. have a large capacity of cation exchange, a property which can be related to their structure. The experiments in this work were carried out with bentonite, a clay with a high content of montmorillonite. Its capacity for absorption of different metals was shown to decrease in the order Cu > Zn > Ni > Cd Laboratory work was carried out with equipment simulating a continuous pipe autoclave. Reaction time was typically 30 min and the temperature could be varied up to279°C. After the treatment, leaching tests were performed at pH 5 and 3. It was shown that the fixation increased with temperature and with the amount of added Na2CO3 or NaHCO3, the effect of the former being slightly greater than the latter. The order of retention was Ni > Cu > Zn > Cd. Only 1.2% of nickel but 35% of cadmium are leached under the same conditions (H2SO4 at pH 3.0-3.1). This probably reflects the adap...