MEAB - Turnkey: SAEC plant in Homs, Syria

Client

Syria, SAEC plant in Homs, Syria

Problem

Purification of Green Phosphoric Acid (H3PO4)

Solution

The project was divided into two phases:

Phase 1

By reacting apatite with sulfuric acid, phosphoric acid and gypsum will result. Most phosphoric acid is produced in this way and normally used as raw material (green acid) to produce fertilizer. A small amount, however is further refined to phosphoric acid of food grade quality.

The green phosphoric acid from a phosphoric acid plant (PAP) contains 25-30% H3PO4. The acid is heavily entrained with impurity cations, among which arsenic, cadmium and uranium are the most poisonous. Also anions, like chloride, fluoride and sulfate must be considered. Selective extraction of phosphoric acid as an adduct complex with TBP and according to the block diagram below has been used to produce acid of food grade. The purification operation starts with addition of chemicals to precipitate arsenic and sulfate in a pre-treatment step. The acid is then cooled and left for an appropriate ageing time. A flocculent is added and the solid content is allowed to flock (precipitate) in a clarifier.

Phase 2

The clear phosphoric acid is fed to the solvent extraction operation, where about 60% of the acid is extracted counter-currently to an organic solvent containing TBP in kerosene. The resulting raffinate with most of the contaminating substances left in the raffinate, together with the slurry from the clarifier, is returned to the phosphoric acid plant. In this way, the impurities in the green acid will be returned to the fertilizer production without creating additional environmental problems.

After extraction the organic solvent, loaded with phosphoric acid, is scrubbed with a phosphoric acid solution in equilibrium with the organic solvent. In this way, co-extracted contamination is removed. The scrub liquor is recycled to extraction.

After adjusting the temperature to about 40 °C, the organic solvent is treated with clean water to strip out the phosphoric acid. From this acid, containing about 30% H3PO4, water is evaporated. The resulting concentrated (85%) phosphoric acid is of good quality, corresponding to the quality of food grade phosphoric acid.

Contact

Dr. Hans Reinhardt, +46 31 685414
hans.reinhardt@meab-mx.se
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