From Wet Crude Phosphoric Acid to High Purity Products

The production of pure phosphoric acid by purification of wet process acid has become economically competitive with thermal phosphoric acid.

Societe de Prayon, a Belgian company, has developed a liquid-liquid extraction process using a mixture of ether and tri-n-butyl phosphate as solvent (patented). The process includes a pre-treatment of the raw weak acid (28-30% P₂O₅) or merchant acid (52-54% P₂O₅).

The original mixture of solvents used gives to the extraction and re-extraction steps some substantial advantages: high extraction capacity and selectivity for phosphoric acid, simplicity and stability in operation, low power consumption.

According to the post-treatment applied to, several purified acid grades can be produced, up to the pharmaceutical grade and up to 62% P₂O₅.

One pure phosphoric acid plant, 33,000 MTPY P₂O₅, is now (1981) running since 1976 in one of Prayon facilities near Antwerp. The white acid produced is sold for a majority of uses reserved up to now to the thermal acid.

A Davister and G Martin, Societe© de Prayon, Belgium.

20 pages, 5 figures, 3 tables.