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.
Highlights
The atmospheric cycle of mercury lasts up to a year and is difficult to control due to its significant environmental prevalence, with its atmospheric pathways capable of affecting thousands of kilometres [1,2]
The operational conclusions of United States power plants showed that the prices of unmodified AC and brominated AC reached USD 1190/ton and USD 2094/ton, respectively
The authors of this publication examined the behaviour during Hg and CO2 removal of raw and biosorbent-modified fly ash and noted the following conclusions: 1. Fly ash from the 1st and 2nd electrostatic precipitator (ESP) zones is effective in removing both Hg and CO2
Summary
The atmospheric cycle of mercury lasts up to a year and is difficult to control due to its significant environmental prevalence, with its atmospheric pathways capable of affecting thousands of kilometres [1,2]. The annual mercury release is estimated at 1000–6000 Mg, contributing to 30–55% of atmospheric mercury [6,7,8]. The anthropogenic mercury emission presents a significant hazard for human health and the environment, leading governments worldwide to make meaningful efforts in its control. The anthropogenic release of CO2 is a significant problem as it heavily contributes to global warming [10]. The global average of CO2 atmospheric content has grown over the past 100 years, with a rise of over 1.6 ppm annually. The atmospheric inventory of this compound is bound to increase as the global emission of fossil fuel-derived CO2 has reached close to 3 ppm [11]. Reducing CO2 emissions will be the most significant industrial challenge of the twenty-first century [12]
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