PHOSPHORIC ACID PRODUCTION METHODS

There are two main industrial processes:

1️⃣ WET PROCESS (Most Common – Fertilizer Grade)

Used for: Fertilizer production (DAP, MAP, TSP), industrial phosphates

PROCESS STEPS

1. Crushing & Grinding of Phosphate Rock

   • Raw material: Fluorapatite (Ca₅(PO₄)₃F)

2. Reaction with Sulfuric Acid (H₂SO₄)
   Main reaction:
   Ca₅(PO₄)₃F + 5H₂SO₄ + 10H₂O → 3H₃PO₄ + 5CaSO₄·2H₂O + HF

3. Formation of Phosphoric Acid + Gypsum

   • Gypsum (CaSO₄·2H₂O) precipitates

   • Phosphoric acid remains in liquid phase

4. Filtration

   • Gypsum cake is filtered out

   • Filtrate is “weak phosphoric acid” (ca. 28–32% P₂O₅)

5. Concentration (Evaporation)

   • Heated under vacuum

   • Final concentration: 52–54% P₂O₅ (75–85% H₃PO₄)

6. Purification (Optional)

   • Clarification, defluorination, solvent extraction if higher purity needed

ADVANTAGES

• Low cost

• High production capacity

• Ideal for fertilizers

DISADVANTAGES

• Contains impurities (Fe, Al, Mg, F)

• Not suitable for food/pharmaceutical grade without purification

---

2️⃣ THERMAL PROCESS (High Purity – Food & Pharma Grade)

Used for: Food-grade, technical-grade, pharmaceutical-grade phosphoric acid

PROCESS STEPS

1. Burning Elemental Phosphorus
   P₄ + 5O₂ → 2P₂O₅ (phosphorus pentoxide)

   • Requires high-purity elemental phosphorus

2. Hydration of P₂O₅
   P₂O₅ + 3H₂O → 2H₃PO₄

   • Forms high-purity phosphoric acid

3. Cooling & Finishing

   • Acid cooled, filtered, and stored

   • Typical concentration: 75–85% H₃PO₄

ADVANTAGES

• Very pure

• Suitable for food, pharmaceuticals, electronics

• Low impurity levels (Fe, Al, F)

DISADVANTAGES

• Very expensive

• Requires elemental phosphorus

• High energy consumption

---

3️⃣ ELECTROTHERMAL PROCESS (Less Common)

Used in some regions where electricity is cheap.

PROCESS

• Phosphate rock → reduced in electric furnace with coke & silica → elemental P

• Elemental P burned to P₂O₅ → hydrated to H₃PO₄
  Essentially a hybrid method leading to high purity acid.

---

COMPARISON TABLE

---

MAIN RAW MATERIALS

• Phosphate rock (fluorapatite)

• Sulfuric acid (wet process)

• Elemental phosphorus (thermal process)

• Water

• Energy/steam

---

BY-PRODUCTS

• Gypsum (CaSO₄·2H₂O) – wet process

• Fluorine compounds (HF, SiF₄)

• Heat/steam