Cement chemistry – making high alumina cement (HAC) High alumina cement is produced by fusing bauxite with which material before clinkering and grinding?

Introduction / Context:
High alumina cement (HAC) is notable for rapid strength gain and chemical resistance. Its manufacture involves creating calcium aluminates, which form during fusion and subsequent cooling of specific raw materials.

Given Data / Assumptions:

• Bauxite supplies alumina (Al2O3).
• We need a calcium source to form calcium aluminates.
• Standard raw mix practice for HAC production is assumed.

Concept / Approach:
HAC consists primarily of calcium aluminates such as CA and CA2. To form these, bauxite (Al2O3) is fused with a calcium source—most commonly limestone (CaCO3), which decomposes to CaO in the kiln. The fused mass (‘‘clinker’’) is then crushed and ground. Other listed materials do not provide CaO in the needed form or are not used for this purpose.

Step-by-Step Solution:

Verification / Alternative check:
Textbook HAC manufacturing routes confirm the use of bauxite and limestone as primary raw materials fused at high temperature to create calcium aluminate phases.

Why Other Options Are Wrong:

• Alum: A sulfate salt; not a calcium source.
• Coke: Fuel/reductant, not a CaO source.
• Quartz: Silica; would form silicates, not desired aluminates.

Common Pitfalls:
Confusing HAC with Portland cement chemistry; HAC emphasizes aluminates rather than silicates and uses a different raw mix and heat treatment.

Final Answer:
limestone