Fly Ash

Fly Ash, also known as coal ash or pulverised fuel ash is a coal combustion product composed of fine particles of burned fuel. It is derived out of coal-fired boilers together with flue gases.

In the past, fly ash was generally released into the atmosphere, but air pollution control standards now require that it be captured prior to release by fitting pollution control equipment.

This article will give details about Fly Ash within the context of the IAS Exam.

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Composition of Fly Ash

The main components of fly ash are believed to be SiO2, Al2O3, Fe2O3 and occasionally CaO as well. Fly ash material solidifies while suspended in exhaust gases.

The minerals that contain in fly ash are just as diverse. Materials like  quartz, mullite and the iron oxides hematite, magnetite and/or maghemite.

Fly ash is classified as Class F and Class C by the American Society for Testing and Materials. The difference between them is the amount of calcium, aluminium and iron content. The chemical makeup of the fly ash is largely determined by the chemical content of the coal burnt.

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Uses of Fly Ash

Fly Ash is used as follows:

1. Construction of Embankments: Though unusual, Fly Ash is used as a construction material for embankments Fly ash has a large uniformity coefficient and has clay-sized particles.The Engineering properties of embankments with the help of Fly Ash are compaction characteristics, shear strength, compressibility, permeability, and frost susceptibility.
2. Soil Stabilization: Soil stabilisation is a process of permanently altering the physical and chemical makeup of soil. The granular property of Fly Ash can enhance the shrink-swell properties of a soil, enabling for subgrade pavements and foundations to be built.
3. Creation of Asphalt Concrete: Asphalt concrete is a composite material consisting of an asphalt binder and mineral aggregate commonly used to surface roads. Fly ash can typically be used as a mineral filler to fill the voids and provide contact points between larger aggregate particles in asphalt concrete mixes.

Environmental Concerns about Fly Ash

1. Groundwater Contamination: Coal, which is a component of Fly Ash, contains elements such as arsenic, barium, boron, selenium and mercury, most of which is toxic to human and animal life. Thus, fly ash obtained after combustion of the coal has potential to pollute groundwater.
2. Ecological Impact: The Ecological effect of fly ash will depend on the type of factory and thermal power plant discharge at play. This is due to the different chemical make-up of the coal based on the geological makeup of the environment. Thus the fly ash that will be deposited on the topsoil will affect the plants and animals in the surrounding area.

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