Mechanisms and Models Describing Sodium and Lead Scavenging by a Kaolinite Aerosol at High Temperatures

Abstract

High temperature mechanisms of interaction between a dispersed kaolinite aerosol and vaporized sodium and lead were investigated using experimental data obtained from an 18 kW downflow furnace. The validity of using aerosol size fractionation to determine the extent of reaction between metal and substrate was confirmed through a series of specialized tests. The reaction stoichiometries for the Na/kaolinite and Pb/kaolinite systems were found to differ from literature values but were similar to each other. New light was shed on the nature of the reaction products for the Na/kaolinite and Pb/kaolinite systems, and for semivolatile metal/kaolinite sorbent systems in general. Modified reaction mechanisms were developed that accommodate key-observed processes (i.e., both enhancing and inhibitory substrate-melting processes). Rate coefficients for each system were quantitatively determined. Mechanisms are interpreted in the light of known information on the structure and nature of kaolin clay and based on observed phase transformations of the Na/kaolinite and Pb/kaolinite systems. The new models for high temperature Na/kaolinite and Pb/kaolinite interactions compared well to both new and literature data. These models can be used to predict and optimize the scavenging of vaporized sodium and lead by kaolinite mineral particles in fossil fuel-fired systems and waste incinerators.