Industrial salts – starting material for alum manufacture Which substance is used as the principal starting raw material for manufacturing alum (e.g., potash alum)?

Introduction / Context:
Alum (commonly potassium aluminium sulfate dodecahydrate) is used in water treatment, paper sizing, and dyeing. The route to alum industrially depends on an aluminium-bearing ore that can be dissolved and converted efficiently.

Given Data / Assumptions:

• Commercial alum production targets Al-bearing feedstocks.
• Bauxite is the most abundant economical source of aluminium compounds.
• Options include pure chemicals and non-aluminium minerals.

Concept / Approach:
Bauxite (a hydrated aluminium oxide ore) is acid-leached to extract aluminium, which is then reacted (commonly with potassium sulfate) to crystallize alum. While alumina is a refined product from bauxite, industry typically references bauxite as the starting raw material for alum manufacture rather than purchasing high-purity alumina for this purpose.

Step-by-Step Solution:

Verification / Alternative check:
Standard inorganic chemical technology texts describe alum preparation from bauxite via acid digestion followed by crystallization with appropriate alkali metal sulfate.

Why Other Options Are Wrong:

• Alumina: A refined material; not the usual ‘‘starting’’ ore feed in bulk alum production context.
• Gypsum: Calcium sulfate; no aluminium.
• Ammonium bicarbonate: Provides ammonium/carbonate; no aluminium.

Common Pitfalls:
Assuming the refined intermediate (alumina) is the designated raw material; in commodity manufacture, the ore (bauxite) is the common starting point.

Final Answer:
bauxite