Liquid-liquid extraction technique for purification of Egyptian WET process phosphoric acid

Abstract

High grade phosphoric acid can be obtained using liquidliquid extraction technique.Different organic solvents were investigated, separately or in mixture, viz.butanol, hexanol, octanol and a mixture of tributylphosphate plus butanol.Among these solvents, n-octanol proved to be the most efficient and selective.The effects of organic solvent concentration, organic/aqueous (O/A) phase ratio, temperature, shaking time and phosphoric acid concentration on P 2 O 5 extraction were studied.The temperature has a slight positive effect and the extraction was enhanced by increasing P 2 O 5 and octanol concentrations and with the increase of organic/aqueous phase ratio.The Mc-Cabe Thiele extraction equilibrium curve showed that an overall extraction yield of more than 80% could be reached over three stages from aqueous solutions.Scrubbing and stripping were also investigated.Scrubbing of the loaded organic acid was done using pure phosphoric acid while stripping of H 3 PO 4 was successfully performed using doubly distilled water (DDW).For 9.2 M H 3 PO 4 , 99.90% of iron, 97.99% of fluoride and 99.99% of manganese were removed whereas complete removal of copper, cadmium and zinc was attained.