Consider the following statements:Statement I: Studies indicate that carbon dioxide emissions from t

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UPSC Prelims is a competitive examination conducted in India. This question is from the 2025 UPSC Prelims Environment & Ecology paper.

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Question

Consider the following statements:Statement I: Studies indicate that carbon dioxide emissions from the cement industry account for more than 5% of global carbon emissions.Statement II: Silica-bearing clay is mixed with limestone while manufacturing cement.Statement III: Limestone is converted into lime during clinker production for cement manufacturing.Which one of the following is correct in respect of the above statements?

Accepted Answer

Correct Answer: C - Only one of the Statements II and III is correct and that explains Statement IStep-by-step Solution:Statement I (Claim): The cement industry accounts for more than 5% of global CO₂ emissions. This is factually correct - the cement sector is responsible for approximately 7-8% of global CO₂ emissions, making it one of the largest industrial emitters.Evaluating Statement II: In cement manufacturing, the raw materials are limestone (CaCO₃) and clay (which provides silica, alumina, and iron oxide). However, the statement says silica-bearing clay- clay naturally contains silica, but the term silica-bearing clay is not standard; more importantly, the raw material mixture also includes other components like iron ore or fly ash. The statement is imprecise and considered incorrect because it implies a specific type of clay rather than the standard clay used. Therefore, Statement II is incorrect. ✗Evaluating Statement III: During clinker production (the most energy-intensive step), limestone (CaCO₃) is heated to approximately 1450°C. At around 850°C, a process called calcination occurs: CaCO₃ → CaO (lime) + CO₂. This calcination of limestone is the primary source of process CO₂ in cement manufacturing (accounting for about 60% of cement-related CO₂ emissions). Additionally, burning fossil fuels to achieve these high temperatures generates more CO₂. This statement is correct and directly explains Statement I - the conversion of limestone to lime releases CO₂, which is the primary reason cement production is a major CO₂ emitter. ✓ (Correct AND explains Statement I)Thus, only Statement III is correct, and it explains Statement I.Why other options are incorrect:Option A: Incorrect. Statement II is not correct, so both are not correct.Option B: Incorrect. Statement II is not correct, so both are not correct.Option D: Incorrect. Statement III is correct, so neither is not correct.Key Concept: Cement manufacturing process: (1) Quarrying raw materials (limestone, clay, iron ore); (2) Grinding and blending (raw meal preparation); (3) Clinkerisation - calcination at ~850°C releases CO₂ from CaCO₃, sintering at ~1450°C forms clinker minerals (alite C₃S, belite C₂S, aluminate C₃A, ferrite C₄AF); (4) Grinding clinker with gypsum to produce Portland cement. CO₂ sources in cement: ~60% from calcination (process emissions), ~40% from combustion. Decarbonisation strategies include: Alternative Cementitious Materials (ACMs) - fly ash, slag; Carbon Capture, Utilisation and Storage (CCUS); Hydrogen or electric kilns; Low-carbon clinker formulations.

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More Questions from Climate Change – Causes, IPCC Reports & Paris Agreement

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