Phosphate rock used in fertiliser manufacture predominantly consists of which mineral species?

Introduction / Context:
Natural phosphate rock is the primary source of phosphorus for fertiliser production. Knowing its dominant mineralogy is important for selecting acidulation conditions, impurity management, and environmental controls for fluoride emissions.

Given Data / Assumptions:

• Feed is geological “phosphate rock.”
• Processing routes include wet-process phosphoric acid and direct acidulation to superphosphates.

Concept / Approach:
Most commercial phosphate rock is a form of apatite, commonly fluorapatite (also called fluoroapatite), with idealised composition Ca5(PO4)3F or equivalently 3Ca3(PO4)2·CaF2. The fluoride in the lattice explains HF/SiF4 evolution during acidulation and the need for fluorine scrubbing.

Step-by-Step Solution:

Verification / Alternative check:
Analyses of sedimentary and igneous phosphate ores consistently report fluorapatite as the principal phase, with variable substitution and impurity content.

Why Other Options Are Wrong:

• Ammonium phosphate: synthetic fertiliser, not a rock mineral.
• Calcium fluoride: occurs as fluorite, not the main P carrier.
• Calcium phosphate (unspecified): too vague; apatite structure is the correct identification.
• Hydroxyapatite only: present in some ores but fluorapatite predominates.

Common Pitfalls:
Equating generic “calcium phosphate” with the specific apatite minerals; process design hinges on the fluoride-bearing nature of fluorapatite.

Final Answer:
fluorapatite (Ca5(PO4)3F)