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Fly ash

Topics Covered: Conservation, environmental pollution and degradation, environmental impact assessment.

Fly ash

What to study?

For prelims: What is fly ash, how is it produced and where it can be used?

For mains: Concerns associated with its contamination, what needs to be done and legislative measures necessary.

Context: While 20 districts of Madhya Pradesh battle hard against the killer onslaught of the novel Coronavirus, the Singrauli district of the central Indian state has been hit by a tragedy caused by the Reliance Power plant’s fly ash dyke collapse.

Background:

The Reliance Power’s Ultra Mega Power Project’s (UMPP) in Sasan area of Singrauli fly ash dyke collapsed recently. The flood of the toxic ash slurry from the collapsed dyke located in adjoining Harhawa village washed away six persons, including three kids, a woman and two men living in the adjoining villages.

What is Fly Ash?

Popularly known as Flue ash or pulverised fuel ash, it is a coal combustion product.

Composition:

  • Composed of the particulates that are driven out of coal-fired boilers together with the flue gases.
  • Depending upon the source and composition of the coal being burned, the components of fly ash vary considerably, but all fly ash includes substantial amounts of silicon dioxide (SiO2), aluminium oxide (Al2O3) and calcium oxide (CaO), the main mineral compounds in coal-bearing rock strata.
  • Minor constituents include: arsenic, beryllium, boron, cadmium, chromium, hexavalent chromium, cobalt, lead, manganese, mercury, molybdenum, selenium, strontium, thallium, and vanadium, along with very small concentrations of dioxins and PAH compounds. It also has unburnt carbon.

Health and environmental hazards:

Toxic heavy metals present: All the heavy metals found in fly ash nickel, cadmium, arsenic, chromium, lead, etc—are toxic in nature. They are minute, poisonous particles accumulate in the respiratory tract, and cause gradual poisoning.

Radiation: For an equal amount of electricity generated, fly ash contains a hundred times more radiation than nuclear waste secured via dry cask or water storage.

Water pollution: The breaching of ash dykes and consequent ash spills occur frequently in India, polluting a large number of water bodies.

Effects on environment: The destruction of mangroves, drastic reduction in crop yields, and the pollution of groundwater in the Rann of Kutch from the ash sludge of adjoining Coal power plants has been well documented.

However, fly ash can be used in the following ways:

  • Concrete production, as a substitute material for Portland cement, sand.
  • Fly-ash pellets which can replace normal aggregate in concrete mixture.
  • Embankments and other structural fills.
  • Cement clinker production – (as a substitute material for clay).
  • Stabilization of soft soils.
  • Road subbase construction.
  • As aggregate substitute material (e.g. for brick production).
  • Agricultural uses: soil amendment, fertilizer, cattle feeders, soil stabilization in stock feed yards, and agricultural stakes.
  • Loose application on rivers to melt ice.
  • Loose application on roads and parking lots for ice control.

The issues which impede its full-scale utilization in India:

  1. Indian fly ash is primarily of the calcareous or class C variety,implying that it possesses not only pozzolanic, but also hydraulic (self-cementing) properties. In contrast, European fly ash is of a silicious or class F variety, implying an absence of hydraulic properties.
  2. The pricing of fly ash is increasingly becoming a contentious issue that is hampering its gainful utilisation.
  3. Imperfections typical of quasi-markets,such as information asymmetry and high transaction costs, vested interests, technical and technological limitations, and the lack of regulatory oversight and political will, have impeded the flow of fly ash to its most value-adding use.

Sources: down to earth.