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.
