Phosphate rock acidulation — Reaction of phosphate rock with dilute sulphuric acid produces which fertilizer product?

Introduction:
Phosphate fertilizers are produced by acidulating phosphate rock (apatite). The choice of acid and its strength determines whether the main product is phosphoric acid, single superphosphate, or triple superphosphate.

Given Data / Assumptions:

• Feed: phosphate rock, mainly apatite (Ca10(PO4)6F2 and related).
• Acid: dilute H2SO4.
• Conventional wet-process acidulation at ambient to moderate temperature.

Concept / Approach:
With dilute sulphuric acid, the principal reaction yields monocalcium phosphate monohydrate in the presence of gypsum: Ca3(PO4)2 + 2 H2SO4 + 4 H2O → Ca(H2PO4)2·H2O + 2 CaSO4·2H2O. The resulting product is called single superphosphate (SSP), a mixture of monocalcium phosphate and gypsum. When phosphoric acid, not dilute sulphuric acid, is used, the product is triple superphosphate (TSP) with higher P2O5 content.

Step-by-Step Solution:
Identify acidulating agent: dilute H2SO4.Write net reaction giving monocalcium phosphate + gypsum.Recognize product trade name: single superphosphate.

Verification / Alternative check:
Fertilizer manuals specify SSP production by sulphuric acid attack; TSP requires phosphoric acid.

Why Other Options Are Wrong:

• Phosphoric acid is produced by stronger acidulation routes, not by dilute H2SO4 on rock alone.
• TSP needs H3PO4, not H2SO4.
• Gypsum is a byproduct with SSP, not the sole product.
• MAP requires ammonia and phosphoric acid, a separate neutralization step.

Common Pitfalls:
Interchanging SSP and TSP processes; overlooking gypsum’s presence in SSP.

Final Answer:
Single superphosphate (SSP)