1. Manufacturing Process of H3PO4 (wet process)
Guided by :
Prof. Sejal solanki
Chemical department
Prepared by :
Chemical engineering department
Government engineering college
Bhuj

2. Wet Process (Strong acid):
The wet process is according to the acids (sulfuric acid, nitric acid or hydrochloric acid) used to decompose the phosphate rock.
The process using sulfuric acid is the most common among all particularly for producing fertilizer grade phosphoric acid.
The wet process phosphoric acid, also called as green acid.

3. Contents to be included
Properties
Raw Materials
Quantitative requirements
Chemical reaction
Flow sheet
Major engineering problems
uses

4. Properties: Phosphoric Acid: Molecular formula : H3PO4
Molecular weight : 98 gm/mole
Melting point : 42.4ºC
Boiling point : 213ºC

5. Raw Materials:
The high grade of imported ore is necessary to avoid solubilization of mined rock impurities such as aluminium, silicon, iron oxide, and alkali minerals.
The only other raw material required is strong sulphuric acid which comes from a contact sulphuric acid plant located at or near the phosphoric acid plant.

6. Quantitative requirements:
Basis:
1 ton of phosphoric acid (100%)
Phosphate rock(32% P2O5) = 2.5 tons
Sulfuric acid(93-98%) = 2 tons
Plant capacity:
tons/day of 100% H3PO4

7. Chemical Reaction:
Ca10F2(PO4) H2SO4 + 20H2O → 10CaSO4.2H2O + 2HF + 6H3PO4

8. Flow Sheet:

9. Process Description:
Sulfuric acid on reaction with phosphate rock along with precipitation of calcium sulfate results into the formation of phosphoric acid.
The process is simple and requires grinding of phosphate rock reacting with dilute phosphoric acid.
so that, melt is produced which in a reactor as mixed with concentrated sulfuric acid for 4 to 8hrs in the temperature range of 75-80°C.
Lot of air is required to control the temperature.

10. The gypsum-phosphoric acid slurry goes to a travelling pan vacuum filter where the 40% acid is removed and the cake washes the water.
The gypsum can either be dried for use in plaster, paints, and cements, or reacted with ammonium carbonates to give ammonium sulphate and calcium carbonate.
The dilute acid is concentrated in a single effect evaporator to any grades >50% acid.
gypsum and phosphoric acid are separated and after minor purification the phosphoric acid is concentrated into the evaporator.

11. Major Engg. Problems: Process design: Material of construction:
Fineness of grind
Temperature
Control of sulphuric acid
Material of construction:
Reaction tank constructed of steel and lined with acid-proof brick.
All air vent systems are PVC coated steel.
Storage tanks of rubber-lined steel.

12. Uses: Used for preparation of hydrogen halides
Used as a "rust converter”.
Food-grade phosphoric acid is used to acidify foods and beverages such as various colas.
Used in many teeth whiteners to eliminate plaque.
As a chemical oxidizing agent for activated carbon production
As a cleaner by construction trades to remove mineral deposits, cementitious smears, and hard water stains.
As a pH adjuster in cosmetics and skin-care products.
As a dispersing agent in detergents and leather treatment.