Gaseous CdCl2 and PbCl2 adsorption by limestone at high temperature: Mechanistic study through experiments and theoretical calculation

There is a risk of heavy metal emission during solid waste incineration, and the capture of gaseous semi-volatile metal by mineral sorbents is an effective method for its pollution control. As a cheap and common additive for combustion industry, limestone is an effective sorbent for controlling various gaseous pollutants, but its high-temperature sorption mechanism for gaseous metal chlorides has not been systematically studied yet. In this study, an experimental study in a fixed bed furnace and density functional theoretical study were conducted to investigate the adsorption mechanism of gaseous CdCl2 and PbCl2 by limestone at high temperature. The capture performance was greater at a higher temperature due to the formation of an enhanced pore structure through limestone decomposition, while the efficiency decreased at temperatures higher than 700 °C because of the negative movement of the reaction equilibrium. Additionally, the higher equilibrium constant of CdCl2 caused more effective adsorption than PbCl2. According to theoretical calculations, both limestone and lime can adsorb molecular metal chlorides while lime has higher adsorption energies due to its more active surface. For a commercial application, it is recommended to inject limestone into the furnace at a high temperature to capture heavy metal more effectively.