Statement I is correct. Studies indicate that carbon dioxide emissions from the cement industry account for more than 5% of global carbon emissions. This significant contribution arises from both the energy-intensive nature of the manufacturing process and the chemical reactions involved.
Statement II is correct. In the manufacturing of cement, silica-bearing clay is indeed mixed with limestone. The subsequent processing of these raw materials at very high temperatures requires a substantial amount of energy, often derived from the combustion of fossil fuels, which leads to indirect CO₂ emissions.
Statement III is correct. During the production of clinker, a key intermediate in cement manufacturing, limestone (CaCO₃) undergoes a process called calcination at temperatures around 1450 °C. This chemical reaction converts limestone into lime (CaO) and directly releases carbon dioxide (CO₂). This process emission is a major contributor to the cement industry's overall CO₂ footprint.
Both Statement II, by highlighting the energy demand for raw material processing, and Statement III, by detailing the direct chemical release of CO₂ from limestone calcination, explain the substantial carbon dioxide emissions from the cement industry as mentioned in Statement I.
Option 2 is incorrect because both Statement II and Statement III are correct and both contribute to explaining the CO₂ emissions described in Statement I. Statement II addresses indirect emissions from energy consumption, while Statement III addresses direct process emissions.
Option 3 is incorrect because both Statement II and Statement III are factually accurate descriptions of processes involved in cement manufacturing.
Option 4 is incorrect as both Statement II and Statement III are correct statements regarding the cement manufacturing process and its associated CO₂ emissions.