Recovery of high grade phosphoric acid from wet process acid by solvent extraction with aliphatic alcohols

High grade phosphoric acid was obtained using liquid–liquid extraction with aliphatic alcohols to separate metal and fluoride ion impurities in the aqueous phase. The influence of alcohol chain length, alcohol concentration, organic/aqueous phase ratio, temperature, shaking time and phosphoric acid concentration on P2O5 extraction was studied. Scrubbing with acid and stripping with water were also investigated. n-Octanol proved to be the most efficient and selective alcohol. The temperature had a slight positive effect and the extraction was enhanced by increasing P2O5 and with the increase of organic/aqueous phase ratio. The optimum organic/aqueous phase ratio for stripping was determined to be 2.0. For 9.2 M H3PO4, 98% of fluoride ion was removed whereas almost complete removal of iron, manganese, copper, cadmium and zinc was attained.

Research Highlights
► Purification of wet process phosphoric acid was achieved using normal aliphatic alcohols.
► P2O5 was extracted from phosphoric acid with O/A equal 1/1, 3/1 and 5/1 for butanol, hexanol and octanol respectively.
► McCabe Thiele Diagrams indicate that 86, 94 and 87% acid extraction in 3 stages.
► Scrubbing of the loaded organic extract containing 25 wt % P2O5 was achieved.
► The stripping efficiencies of the alcohols follow the order: octanol > hexanol > butanol.