Behaviours of MeCl₂ (Me: Pb and Cd) during thermal treatment of kaolin-lime mixture

Abstract

This paper reports the emission behaviours of Pb and Cd during heat treatment of their chloride salts with kaolin-lime and kaolin-lime-silica mixtures. The leaching behaviours of Pb and Cd from the heattreated products are also assessed. The results showed that the addition of lime into kaolin increased the emitted amounts of Pb and Cd during heating. Addition of silica into the mixtures further increased the emissions of both elements at low temperature (≤1000°C) and inhibited their emissions at high temperature (≥1100°C). Crystallinity of silica had profound effect on the emissions of Pb and Cd from the mixtures. The heat-treated product containing anorthite as the major crystalline phase not only retain more amounts of Pb and Cd in its composition but also emit lesser amounts of Pb and Cd into solution than the product containing gehlenite as the major crystalline phase during subjected leaching test.

Key words: Toxic element,kaolin, lime, silica, heat-treatment, leaching.