Blast furnace practice — typical composition of slag The slag floating on molten iron in a blast furnace typically contains which constituents (approximate percentages by weight)?

Introduction / Context:
Blast furnace slag composition is central to ironmaking and affects fluidity, desulphurization, and subsequent utilization (e.g., slag cement). Construction engineers encounter slag in cementitious materials and need awareness of its typical makeup.

Given Data / Assumptions:

• Representative hot metal operation with limestone/dolomite fluxes.
• Percentages are approximate and vary with burden composition.

Concept / Approach:
Flux additions combine with gangue to form slag. A basic slag commonly contains significant CaO, SiO2, and Al2O3, with minor MgO and iron compounds. The basicity (CaO/SiO2 ratio) influences sulphur removal and viscosity. The figures given represent a typical balanced slag.

Step-by-Step Solution:
Recognize major oxides: CaO, SiO2, Al2O3 dominate.Acknowledge minor species: MgO and iron-bearing compounds round out the composition.Select the option that includes all components and percentages.

Verification / Alternative check:
Slag chemistry control charts from ironmaking practice show CaO ~ 40–50%, SiO2 ~ 30–40%, Al2O3 ~ 10–15%, plus MgO and traces, consistent with the listed values.

Why Other Options Are Wrong:
Choosing any single constituent ignores the full typical composition; the comprehensive choice is appropriate.

Common Pitfalls:
Confusing blast-furnace slag with steelmaking slag, which can have different basicity and metallic content.

Final Answer:
All of the above