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

Société 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, Société de Prayon, Belgium.

20 pages, 5 figures, 3 tables.