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

Abstract

High grade phosphoric acid can be obtained using liquid-liquid 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 P₂O₅ extraction were studied. The temperature has a slight positive effect and the extraction was enhanced by increasing P₂O₅ and octanol concentrations and with the increase of organic/aqueous phase ratio. The McCabe 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 H₃PO₄ was successfully performed using doubly di stilled water (DDW). For 9.2 M H₃PO₄, 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.