Dissolution and Leaching of Fly Ash in Nitric Acid Using Automated Scanning Electron Microscopy

This article studies the physical and chemical changes in two Class F fly ashes exposed to 3 % HNO3 solution for 15 min. Automated scanning electron microscopy was used to simultaneously determine the physical and chemical properties of thousands of individual particles before and after being exposed to the solution., Exposure for 15 min in the HNO3 solution resulted in the selective dissolution of particles containing over 30 % CaO content but did not cause significant physical or chemical changes in other particles for both fly ashes. In addition, the leaching of sulfur was observed from all particles. Two possible mechanisms are discussed. This work reveals that fly ash particle dissolution is not homogenous and is dependent on the chemical consistency of the particle. This work provides new insights into fly ash dissolution in aqueous solutions and characterization.