Correlation Between Heavy Metal Adsorption Capacity and Thermal Behavior of Acid‐Activated Kaolin During Coal Combustion

ABSTRACT In this work, the retention properties of heavy metals (Pb, Zn, Cr, Cu) by raw/acid‐modified kaolin during coal combustion were studied in the temperature range of 600°C–1200°C, and the effect of acid treatment on the high‐temperature thermal transformations of kaolin was revealed using various characterization methods. The combustion experimental results showed that the sulfuric acid–modified kaolin improved its ability to retention of heavy metals at most temperatures. Compared with the raw kaolin, the modified kaolin improved the retention of lead by up to 47.13% at 800°C, zinc/chromium by up to 27.58%/14.03% at 1000°C, and copper by up to 12.98% at 1200°C. In the temperature range of 600°C–1000°C, higher oxygen concentration favored the retention of modified kaolin for lead and zinc. When the temperature reached above 1000°C, higher oxygen concentration promoted the retention of modified kaolin for chromium and copper. The excellent heavy metal adsorption performance of the modified kaolin were largely due to the rapid and easy removal of hydroxyl groups, the high amorphization of silica–alumina and the excellent pore structure, which could expose more active sites to promote the immobilization of heavy metals in aluminosilicate form.