Modified Fly Ash-Based Adsorbents (MFA) for Mercury and Carbon Dioxide Removal from Coal-Fired Flue Gases

Abstract

One of the solid waste produced during the combustion of coal are fly ashes. Disposal challenges and environmental consequences are the results of significant process yield and atmospheric emission of fly ashes. The exact chemical composition of FA depends mainly on the type of utilised fuel and combustion conditions. It consists mainly of chemically stable metal oxides, such as Al2O3, Fe2O3, SiO2, CaO, MgO, K2O, Na2O and TiO2, but its toxicity is related to the possible presence of some trace elements, such as As, Hg, Cd, Se and Cr. The chemical and physical properties of fly ash (e.g., particle size distribution, porosity, and surface area) make it suitable as an adsorbent to remove various impurities from process flows such as flue gas stream. Its suitability for capturing mercury from flue gas was experimentally confirmed due to its abundant supply, particle size, bulk density, porosity, chemical composition and low cost. Hence, the use of fly ash as adsorbents and precursors for the production of heavy metal adsorbents is of great practical importance, as it reduces the cost of mercury capture and alleviates the problems associated with the disposal of solid waste. Studies showed that the chemical components present in fly ash additives could stimulate catalytic oxidative capacity, which increases the adsorption of Hg0 oxidation and adsorption of both Hg and CO2. The presented study analysed fly ashes from different zones of the electrostatic precipitator and verified their suitability for removing impurities from flue gases, i.e., mercury and carbon dioxide. The results outlined modified fly ash as having good Hg and CO2 removal capabilities. The adsorption efficiency of Hg reached 92% for Hg and 66% for CO2, while untreated fly ash reached 67% for Hg and 59% for CO2.