Question map
With reference to 'fly ash' produced by the power plants using coal as fuel, which of the following statements is/are correct? 1. Fly ash can be used in the production of bricks for building construction. 2. Fly ash can be used as a replacement for some of the Portland cement contents of concrete. 3. Fly ash is made up of silicon dioxide and calcium oxide only, and does not contain any toxic elements. Select the correct answer using the code given below.
Explanation
The correct answer is option A (statements 1 and 2 are correct).
Fly ash bricks are light in weight and offer high strength and durability[1], confirming statement 1 is correct. Cement can be replaced by fly ash upto 35%, thus reducing the cost of construction, making roads, etc[1], which validates statement 2.
However, statement 3 is incorrect. Fly ash contains many hazardous substances within its composition in addition to substantial amounts of silicon dioxide (SiO2) and calcium oxide (CaO)[2]. This clearly shows that fly ash is not composed solely of silicon dioxide and calcium oxide, but also contains toxic elements and hazardous substances.
The beneficial uses of fly ash are further supported by additional applications: Fly ash can be used in reclamation of wastelands, abandoned mines can be filled up with fly ash, and fly ash can increase the crop yield and it also enhances water holding capacity of the land[1].
Sources- [1] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 5: Environmental Pollution > Advantages: > p. 67
PROVENANCE & STUDY PATTERN
Full viewThis is a classic 'Sitter' disguised as a technical question. Statement 3 is a logical suicide—claiming an industrial waste product is 'chemically pure' and 'non-toxic' contradicts the very definition of pollution. The positive applications (Statements 1 & 2) are standard textbook material found in every basic Environment module (e.g., Shankar IAS).
This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.
- Statement 1: Can fly ash produced by coal-fired power plants be used to manufacture bricks for building construction?
- Statement 2: Can fly ash produced by coal-fired power plants be used as a partial replacement for Portland cement in concrete?
- Statement 3: Is fly ash produced by coal-fired power plants composed only of silicon dioxide (SiO2) and calcium oxide (CaO)?
- Statement 4: Does fly ash produced by coal-fired power plants contain toxic elements or heavy metals?
- Explicitly names 'fly ash bricks' and states they are light-weight with high strength and durability.
- Notes that fly ash can replace cement (up to 35%), indicating its suitability in building materials and masonry.
- Recommends promotion of using fly ash from industries as an alternative for construction purposes.
- Frames fly ash use in construction as a viable/encouraged option, supporting practical application.
- Describes how fly ash is collected (electrostatic precipitators), indicating an available, capturable feedstock for manufacturing.
- Supports feasibility by showing fly ash is a recoverable byproduct from coal-fired plants.
- Directly states cement can be replaced by fly ash up to 35%, indicating practical partial substitution.
- Mentions specific construction uses (concrete roads, fly ash bricks), showing suitability in cementitious applications.
- Explicitly recommends promoting use of fly ash from industries for construction purposes, supporting its adoption as a substitute.
- Provides a policy/supply-side endorsement that complements the technical replacement claim in snippet 1.
- Explicitly states fly ash contains many hazardous substances in addition to substantial amounts of SiO2 and CaO.
- Provides a list of other elements (arsenic, beryllium, boron, cadmium, chromium, etc.), directly contradicting the claim that fly ash is composed only of SiO2 and CaO.
- Gives standard chemical composition for fly ash classes showing SiO2 is combined with aluminum oxide and iron oxide as major components.
- Shows Al2O3 and Fe2O3 are significant constituents, so fly ash is not comprised solely of SiO2 and CaO.
- Notes that components of fly ash vary considerably depending on coal source, though all include substantial SiO2 and CaO.
- Implying variability in composition contradicts the idea that fly ash is composed only of SiO2 and CaO.
Explicitly lists fly ash as 'oxide rich' and consisting of silica, alumina, oxides of iron, calcium, magnesium and toxic heavy metals — showing a multi-component mixture rather than only SiO2 and CaO.
A student could combine this with basic knowledge that coal contains diverse mineral matter to infer fly ash likely contains multiple oxides and trace metals beyond just SiO2 and CaO.
Recommends use of fly ash in construction, implying fly ash has properties (e.g., pozzolanic activity) associated with components like silica and alumina, not only SiO2 and CaO.
Knowing construction uses rely on alumina/silica chemistry, a student could suspect other constituents (e.g., Al2O3) are present and important.
Describes common crustal minerals (feldspar, quartz, bauxite) that contain silicon, oxygen, aluminium, calcium — suggesting ashes from burnt mineral-rich fuel will reflect varied mineral chemistry.
A student could use a basic map of mineral composition of coal-bearing rocks to infer fly ash will include oxides of Al, Si, Ca and other cations from those minerals.
Notes coal contains a significant 'ash' fraction (e.g., 20–35% ash in some coals), indicating substantial mineral residue remains after combustion.
Combining this with the idea that coal's mineral matter is chemically diverse, a student could infer fly ash composition is likewise multi-component rather than limited to two oxides.
Explains that burning material produces ash and that combustion ash can be 'toxic' and polluting, implying presence of varied harmful elements rather than just inert SiO2 and CaO.
A student could extend this to expect trace toxic metals or varied oxides in fly ash and thus question the 'only SiO2 and CaO' claim.
- Explicitly reports that fly ash from a thermal power plant entered groundwater and polluted the entire ecosystem, showing fly ash can carry pollutants that cause environmental harm.
- Demonstrates real-world contamination linked to fly ash, supporting the claim that fly ash contains harmful constituents.
- Identifies toxic heavy metals (manganese, copper, cadmium, aluminium) as contributors to detrimental effects on vegetation, establishing that such metals are recognized environmental toxins.
- Provides plausible candidate pollutants that could be present in industrial/ash-related contamination scenarios.
- Lists heavy metals (copper, chromium, cadmium, mercury, etc.) as common pollutants from mining and industrial wastes, indicating industrial activities often release heavy metals into the environment.
- Supports the inference that industrial byproducts (including ashes/particulates) can contain heavy metals that contaminate water and soil.
- [THE VERDICT]: Sitter. Solvable purely by logic (Statement 3 is extreme) or basic reading of Shankar IAS Chapter 5 (Environmental Pollution).
- [THE CONCEPTUAL TRIGGER]: Pollution > Solid Waste Management > 'Waste to Wealth' (Industrial Byproducts).
- [THE HORIZONTAL EXPANSION]: Memorize the 'Big 4' Industrial Wastes: 1. Fly Ash (Coal -> Cement/Bricks, contains Arsenic/Lead); 2. Blast Furnace Slag (Steel -> Cement/Roads); 3. Red Mud (Bauxite -> Highly Alkaline/Hazardous); 4. Phosphogypsum (Fertilizer -> Soil amendment/Roads). Know their specific toxic contaminants.
- [THE STRATEGIC METACOGNITION]: When studying pollutants, move beyond 'it causes asthma'. Create a 3-column table: Composition (What's inside?), Toxicity (Why is it bad?), and Application (How do we recycle it?). UPSC focuses on the 'Application' column for policy questions.
Directly relates to using fly ash in bricks and as partial cement replacement, as stated in the references.
High-yield for UPSC because it links environment, industry and infrastructure topics: material substitution in construction, pollution mitigation via resource use, and cost/efficiency aspects. Learn typical uses and stated replacement rates (e.g., up to 35%) and advantages to answer questions on sustainable construction and allied policies.
- Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 5: Environmental Pollution > Advantages: > p. 67
- Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 6: Environmental Issues > Suggestions > p. 115
Fly ash use in bricks and land reclamation exemplifies reuse of industrial residues.
Frequently tested across environment and governance sections—covers waste-to-resource policies, pollution control measures and sustainable development. Master examples (fly ash bricks, reclamation) and policy rationale to handle questions on circular economy and industrial waste management.
- Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 5: Environmental Pollution > Advantages: > p. 67
- Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 6: Environmental Issues > Suggestions > p. 115
Shows how fly ash is captured at power plants, explaining its practical availability for manufacturing purposes.
Useful for questions linking pollution control technology with material supply chains and regulatory measures. Understand capture methods (e.g., electrostatic precipitators) to explain feasibility and constraints in using industrial byproducts.
- Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 5: Environmental Pollution > How it is collected? > p. 66
Reference 1 gives a concrete numeric guideline that cement can be replaced by fly ash up to 35%, directly answering the statement's technical claim.
High-yield for environment/industry questions: shows an intersection of pollution management and construction materials. Helps answer questions on sustainable alternatives in infrastructure and policy recommendations. Memorise the typical replacement range and related construction uses; link this concept to topics on waste management and building materials in essays and prelims/mains.
- Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 5: Environmental Pollution > Advantages: > p. 67
Reference 2 describes how fly ash is captured (electrostatic precipitators), establishing its origin and availability for use.
Useful for questions on industrial waste streams and mitigation: connects power generation technology to material reuse. Understand capture mechanisms and logistics to discuss feasibility of large-scale utilisation of industrial byproducts in infrastructure planning.
- Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 5: Environmental Pollution > How it is collected? > p. 66
Reference 3 recommends promoting use of fly ash in construction, linking technical possibility to policy/action.
Important for policy-oriented UPSC questions: shows how environmental policy can encourage reuse of waste in construction, reducing costs and pollution. Prepare to discuss policy instruments, benefits, and implementation challenges; link to topics on sustainable development and infrastructure.
- Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 6: Environmental Issues > Suggestions > p. 115
Reference [1] lists multiple major oxides (silica, alumina, iron, calcium, magnesium) and toxic heavy metals in fly ash, directly addressing the composition question.
High-yield for environmental and industrial topics: knowing that fly ash is a complex mix (major oxides + trace heavy metals) helps answer questions on pollution, waste management, and material reuse. Connects to topics on industrial emissions, waste classification, and environmental health. Prepare by memorising common components and examples of trace toxics, and practice applying composition knowledge to policy/regulation questions.
- Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 5: Environmental Pollution > Composition > p. 66
Red Mud (Bauxite Residue). Like Fly Ash, it is a massive industrial waste challenge. Key properties: Highly Alkaline (pH 10-13), rich in Iron Oxide (hence red), and difficult to utilize compared to Fly Ash. Expect a question comparing Red Mud and Fly Ash utilization.
The 'Purity in Pollution' Paradox. Industrial combustion is a messy process. It is chemically impossible for a raw byproduct like ash to be composed of 'only' two specific oxides without any trace impurities. Statement 3's claim of 'no toxic elements' contradicts the very existence of environmental regulations governing it. If it weren't toxic, we wouldn't need laws to manage it.
Mains GS-3 (Science/Environment) link: 'Critical Mineral Recovery'. Recent research focuses on extracting Rare Earth Elements (REEs) from Coal Fly Ash. This bridges Environmental Management with Strategic Resource Security.