Abstract
Fly ash or coal fly ash causes major global pollution in the form of solid waste and is classified as a “hazardous waste”, which is a by-product of thermal power plants produced during electricity production. Si, Al, Fe Ca, and Mg alone form more than 85% of the chemical compounds and glasses of most fly ashes. Fly ash has a chemical composition of 70–90%, as well as glasses of ferrous, alumina, silica, and CaO. Therefore, fly ash could act as a reliable and alternative source for ferrous, alumina, and silica. The ferrous fractions can be recovered by a simple magnetic separation method, while alumina and silica can be extracted by chemical or biological approaches. Alumina extraction is possible using both alkali- and acid-based methods, while silica is extracted by strong alkali, such as NaOH. Chemical extraction has a higher yield than the biological approaches, but the bio-based approaches are more environmentally friendly. Fly ash can also be used for the synthesis of zeolites by NaOH treatment of variable types, as fly ash is rich in alumino-silicates. The present review work deals with the recent advances in the field of the recovery and synthesis of ferrous, alumina, and silica micro and nanoparticles from fly ash.
Highlights
Fly ash or coal fly ash (CFA) is a spherical, glass-like, heterogeneous particle produced as a by-product from the combustion of pulverized coal during electricity production in thermal power plants (TPPs)
As fly ash is derived from coal, which is rich in minerals, fly ash is rich in silica, alumina, and ferrous [3], which are the three major contents of fly ash
The chemical methods initially involve the extraction of sodium silicate from the fly ash using strong hydroxides followed by neutralization by sol-gel technique, whereas microbial synthesis has been carried out using Fusarium oxysporum under optimized conditions
Summary
Fly ash or coal fly ash (CFA) is a spherical, glass-like, heterogeneous particle produced as a by-product from the combustion of pulverized coal during electricity production in thermal power plants (TPPs). If nanoparticles are synthesized from any of the above-mentioned waste, the final product will be cost-effective, and eco-friendly thanks to the minimization of the solid waste as pollution One such precursor material for the synthesis of silica, alumina, and ferrous nanoparticles is fly ash. None of the earlier reported work focused on the recovery of all the three minerals—i.e., ferrous, alumina and silica from fly ash None of these works reported the fate of final fly ash residual material left after the extraction of ferrous, alumina and silica, as it becomes highly reactive after NaOH treatment or silica extraction, which may pose a potential threat to the environment after disposal. The current review highlights the work advancement in the recovery of ferrous, alumina and silica and their subsequent conversion into nanoparticles of high yield and purity
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