Commercial nitric acid production route in fertilizer complexes:\nWhich process is used at scale to make nitric acid?

Introduction / Context:
Nitric acid is a cornerstone intermediate for nitrate fertilizers and explosives. Modern fertilizer plants use the Ostwald process, which oxidizes ammonia to NO, then to NO2, followed by absorption in water to form HNO3. Recognizing the mainstream industrial route is essential for process engineers and students of fertilizer technology.

Given Data / Assumptions:

• Large-scale, continuous production is implied.
• Ammonia is available on-site from Haber–Bosch synthesis.
• Electric arc processes are historical and energy-inefficient.

Concept / Approach:
The Ostwald process dominates: NH3 is catalytically oxidized over Pt–Rh gauze to NO, then further oxidized to NO2 and absorbed to HNO3. Alternative reactions such as double-decomposition of calcium nitrate with sulphuric acid are not standard large-scale nitric acid routes; electric arc nitrogen fixation is obsolete due to high power demand.

Step-by-Step Solution:
Identify the modern industrial method: oxidation of ammonia.Note subsequent steps: NO → NO2 → absorption to HNO3.Select the Ostwald process as the correct route.

Verification / Alternative check:
Process flow diagrams for all contemporary nitric acid units center on the ammonia oxidation converter and absorption tower sequence.

Why Other Options Are Wrong:
Calcium nitrate with sulphuric acid is not a standard HNO3 manufacturing route; electric arc processes are historical; “none” contradicts established practice; direct hydration without oxidation is incomplete.

Common Pitfalls:
Confusing production of nitric acid with production of nitrate salts, which may involve different reactions downstream.

Final Answer:
Oxidation of ammonia (Ostwald process)