Study on Purification of Low Concentration Wet-Process Phosphoric Acid by Composite Extractant

An extraction-washing-reverse extraction-refine extraction process was investigated for 15%~21% wet-process phosphoric acid(WPA)by alcohol-ester composite extractant.The results showed that the optimum process conditions were as follows:the ratio of extraction phase was 4∶1,the extraction temperature was 50℃,the extraction time was 10 min,and the sulfuric acid dosage was 1.5% of WPA mass,the extraction rate was up to 78.6% after extraction for two times and the removal rate of Fe2+ and SO2-4was above 90%.SO2-4 was removed with 0.3%~0.4%(based on the mass of the water lotion)BaCO3 after acid-washing and reverse extraction.Then,phosphoric acid solution was concentrated and bleached.Finally,the 85% industrial phosphoric acid was gained.