Cement manufacture — which raw material is most commonly used as the principal source of calcium in Portland cement production? Select the correct rock.
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ASlate
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BSandstone
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CLimestone
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DBasalt
Answer
Correct Answer: Limestone
Explanation
Introduction / Context:Portland cement clinker is produced by sintering a precisely proportioned raw mix dominated by calcium oxide, along with silica, alumina, and iron oxides. The main calcium source is a decisive choice for plant location and quarrying strategy.
Given Data / Assumptions:
- We consider standard Portland cement manufacture.
- Primary requirement: CaCO3-rich feedstock.
- Auxiliary sources supply silica, alumina, and iron.
Concept / Approach:Limestone (calcium carbonate) is the principal raw material supplying CaO upon calcination. It is abundant, quarried easily, and blends well with shale/clay/iron correctives to achieve kiln feed chemistry. Slate, sandstone, and basalt lack the necessary high CaCO3 content to serve as the main calcium source in typical cement plants.
Step-by-Step Solution:
1) Identify dominant oxide in clinker: CaO ~ 60–67%.2) Map to raw rock: limestone provides CaCO3 for CaO after calcination.3) Evaluate alternatives: slate/sandstone/basalt are silica/alumina-rich or mafic; not primary Ca source.4) Conclude: limestone is the correct answer.Verification / Alternative check:All major cement plants are co-located with limestone quarries to secure long-term, high-CaCO3 feed.
Why Other Options Are Wrong:
- Slate/Sandstone/Basalt: Do not provide the high calcium carbonate content required.
Common Pitfalls:Confusing corrective additives with the principal calcium-bearing raw rock.
Final Answer:Limestone