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

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.