Study on removal of Fe3+ from sodium dihydrogen phosphate by emulsification solvent extraction

Abstract

Wet-process phosphoric acid (WPA) is gradually paid attention to in recent years. However, there are some undesirable impurities (Fe3+, Al3+, Mg2+) in WPA, which will degrade the quality of sodium dihydrogen phosphate (NaH2PO4) products. To get the superior grade NaH2PO4, the WPA should be purified. Enhancing the pH of the solution, often to 4, can remove most of the metal ions, but there is still some Fe3+ which has great effect on the NaH2PO4 crystal products, seem to be irregular long strips. Therefore, before the neutralized NaH2PO4 solution is concentrated, the Fe3+ must be removed.The emulsification extraction of Fe3+ from sodium dihydrogen phosphate (NaH2PO4) solution by di(2-ethylhexyl)phosphoric acid (D2EHPA) is investigated. The good extraction efficiency of Fe3+ with D2EHPA from NaH2PO4 solution by emulsification extraction is verified. Meanwhile, to study the advantages of the emulsification extraction process, the major influencing factors, such as the D2EHPA volume fraction, the phase volume ratio, the initial pH of NaH2PO4 solution, the stirring time and agitation speed on the extraction efficiencies of Fe3+, are studied, and the optimal process conditions are obtained. The results of extraction experiments from practical NaH2PO4 solution show that superior grade NaH2PO4 can be obtained by three stages of extraction under appropriate condition.