High-alumina refractories from pure bauxite: for bauxite-based bricks made from high-grade (nearly pure) bauxite, the maximum alumina (Al2O3) content achievable in commercial products can be as high as approximately what percent?

Introduction / Context:
High-alumina refractories are specified where elevated softening temperature, strong resistance to slag attack, and good creep performance are required. Bauxite—especially when of very high purity—is a major raw material for such bricks. This question asks about the upper bound of alumina content that practical, commercially produced, bauxite-derived refractories can achieve.

Given Data / Assumptions:

• Raw material: high-grade bauxite (calcined) or bauxite refined to concentrate Al2O3.
• Context: commercial refractory products rather than laboratory specimens.
• Alumina content refers to overall composition of the finished brick.

Concept / Approach:
By selecting high-grade bauxite, controlling impurities (Fe2O3, TiO2, alkalis), and employing appropriate firing or fusion processes, bauxite-based refractories can reach very high alumina contents. While common high-alumina lines range from 50–80% Al2O3, premium bauxite-based or fused-refined products can approach about 90% Al2O3, edging toward corundum-rich compositions that deliver superior hot properties. Above this, specialty fused alumina or tabular alumina becomes the predominant feedstock rather than ordinary bauxite.

Step-by-Step Solution:
Identify typical ranges: standard high-alumina bricks (50–80% Al2O3).Recognize premium bauxite-based formulations can be pushed higher with processing.Select the maximum practical figure offered among choices: ~90% Al2O3.

Verification / Alternative check:
Supplier catalogues show bauxite-based bricks at 85–90% Al2O3 in premium series, confirming that ~90% is achievable without moving fully to pure fused alumina systems.

Why Other Options Are Wrong:
55% and 65%: represent mid-grade high-alumina levels, not the maximum.70% and 80%: common, but still below the achievable upper limit with very pure bauxite feeds.

Common Pitfalls:
Assuming bauxite cannot produce ultra-high alumina bricks; processing quality and raw material purity are decisive.Confusing “alumina bricks” with “fused alumina” products, which may exceed 90% but use different feedstocks.

Final Answer:
90%