Triple superphosphate (TSP) manufacture: phosphate rock is acidulated using which mineral acid to produce TSP fertilizer?

Introduction / Context:
Phosphate fertilizers are produced by reacting phosphate rock (apatite) with acids to render phosphorus water-soluble and plant-available. Triple superphosphate (TSP), a high-analysis product, differs from single superphosphate (SSP) in both acid used and final P2O5 content.

Given Data / Assumptions:

• Phosphate rock is mainly fluorapatite.
• Goal: obtain a concentrated, water-soluble phosphate fertilizer (TSP).
• Industrial practice distinguishes SSP vs. TSP by choice of acid and resulting composition.

Concept / Approach:
SSP is produced by treating rock phosphate with sulphuric acid, generating monocalcium phosphate and gypsum (CaSO4·2H2O) as by-product. TSP, by contrast, is made by acidulating rock with phosphoric acid, avoiding gypsum formation and yielding a higher P2O5 content (~46% P2O5 in TSP). Thus, the acid that specifically identifies TSP manufacture is phosphoric acid.

Step-by-Step Solution:
Identify the product: TSP (triple superphosphate).Recall the process: rock phosphate + phosphoric acid → monocalcium phosphate without gypsum dilution.Therefore, select “Phosphoric acid”.

Verification / Alternative check:
Process descriptions in fertilizer technology texts consistently cite phosphoric acid for TSP and sulphuric acid for SSP, explaining the different by-products and analysis levels.

Why Other Options Are Wrong:
Nitric acid is used in nitrophosphate processes; sulphuric acid corresponds to SSP; hydrochloric/acetic acids are not used industrially for TSP manufacture.

Common Pitfalls:
Mixing up SSP and TSP chemistry; remembering “triple” corresponds to using phosphoric acid and getting higher grade.

Final Answer:
Phosphoric acid