Mining Operations
Chemical Processing
  Manufacturing processes   
 
Sulphuric acid
As a general rule, the manufacture of sulphuric acid is made in 3 stages :
• Combustion, which consists in burning sulphur in a furnace to obtain sulphur dioxide (SO2).
• Conversion, which consists in combining sulphur dioxide with oxygen in a converter to obtain sulphur trioxide (SO3).
• Absorption, which consists in combining sulphur trioxide with water in absorption towers in order to obtain a solution containing 98 to 99% of sulphuric acid (H2SO4). In Jorf Lasfar and in one production line at Maroc Chimie (Safi), this operation is made in 2 stages (double absorption) to minimize S03 emission in the atmosphere.

The various processes used are: Monsanto single or double absorption, Polimex.
Phosphoric acid
The phosphoric acid manufacturing process used is the wet process, where acid is obtained by direct attack of mineral phosphate by a strong acid (sulphuric acid). It is widely used in the world because it has the advantage of producing acid at low cost. The main wet processes are: Rhone-Poulenc, Prayon, Nissan, Mitsubishi.
The three main stages are :
• Crushing: The purpose of crushing phosphate rock is to increase the mineral surface of attack by sulphuric acid.
• Attack-filtration: Crushed phosphate rock is attacked by 98.5% concentrated sulphuric acid and medium phosphoric acid (18 to 22% P2O5) in aqueous mediums. The mixture gives a slurry. Filtration of this slurry consists in separating 29% P2O5 phosphoric acid from phosphogypsum using a rotary filter. The product is then stored in settling tanks .
• Concentration: The aim of concentrating phosphoric acid is to allow water evaporation in order to have a 54% P2O5 acid.
Fertilizers
The manufacture of fertilizers is based on a reaction between phosphoric acid and ammonia (for DAP, ASP, MAP and NPK) and on attack of phosphate rock with phosphoric acid (for TSP).
Concerning DAP, MAP and ASP fertilizers, the method initially consists in neutralizing phosphoric acid by ammonia with presence of sulphuric acid. The resulting slurry is taken to a granulator. The product obtained from the granulated is introduced into a drier heated by gases coming from a combustion chamber.
When it comes out of the dryer, the product undergoes selection by screening. The merchant grade obtained this way is cooled then coated with fuel oil in order to avoid caking during its storage.
In the case of NPK, the process is identical, except that ammoniation is complemented by addition of potash in the granulator.

TSP manufacturing is based on the reaction of crushed phosphate rock with 42% P2O5 phosphoric acid. The attack is then supplemented by progressive drying of the slurry. After granulation, the product undergoes selection in vibrating sieves, grinders and crushers.

The various manufacturing processes are: AZF, Jacobs, Fisons Manifos