Production of lime for construction – identifying the correct source process Which statement correctly describes how quicklime (CaO) is obtained for use in building works?

Introduction:
Lime is a fundamental binder used historically in mortars, plasters, soil stabilization, and whitewashing. The question checks your understanding of the industrial process used to produce quicklime (calcium oxide) from natural raw materials such as limestone and chalk.

Given Data / Assumptions:

• Calcium carbonate sources: limestone, chalk, shells, etc.
• Target product: quicklime (CaO), not hydrated lime (Ca(OH)2).
• Process temperature is approximately in the neighborhood of 900°C or higher depending on kiln and material.

Concept / Approach:

The key reaction is thermal decomposition of calcium carbonate (calcination). Heating CaCO3 drives off carbon dioxide and yields calcium oxide, which is then slaked with water to produce hydrated lime. Dissolving carbonates in water does not yield CaO, and calcium chloride is a different compound entirely.

Step-by-Step Solution:

Verification / Alternative check:

Industry practice and civil engineering texts universally describe lime manufacture as calcination of carbonate rocks. Operational temperatures around 900°C–1000°C are typical for efficient decomposition.

Why Other Options Are Wrong:

Free state: Lime does not occur naturally in a stable free state; it reacts readily with moisture and CO2.

Dissolving CaCO3 in water: Produces a slurry/suspension, not CaO.

Calcium chloride: CaCl2 is a different salt used as a set accelerator or dehumidifier, not lime.

None of these: Incorrect because calcination is correct.

Common Pitfalls:

Confusing lime types (quicklime vs hydrated lime); mixing up CaO with CaCl2; overlooking that calcination releases CO2.

Final Answer:

Lime is obtained by calcining calcium carbonate at about 900°C