Performances of nanofiltration on industrial phosphoric acid purification

Abstract

Phosphoric acid production is of major importance to the Tunisian economy. However, the quality produced is not suitable for other than agricultural use due to mineral and organic impurities. In this study, the purification of industrial phosphoric acid with a maximum P₂O₅ concentration of 25% was achieved by nanofiltration.  Six solutions of different P₂O₅ concentration were used. The removal of organic (total carbon) and inorganic impurities such as magnesium, iron, chrome, zinc, cadmium and vanadium, were studied.

The performances of nanofiltration (NF) Nadir NP 30 membrane were determined in terms of permeate flux and P₂O₅ and impurities retention taking into account the effect of transmembrane pressure, P₂O₅ concentration and membrane prea-treatment by purified phosphoric acid solution.

Results showed that for the industrial 25% P₂O₅ acid solution, the use of NF membrane achieved a retention of 87.35%, 86.73%, 87.57%, 78.41% and 73.17%, respectively, for iron, aluminum, chrome, magnesium, vanadium and organic matter (kerogen and humic acids) under a pressure of 20 bar. P₂O₅ permeation increased with the increase of its concentration in the acidic feed solution. The best permeation is provided by 25% P₂O₅ feeding acid solution which is of almost 98%.