Extraction of nitric acid from wet-process phosphoric acid

Abstract

Solvent extraction of nitrates (almost all as nitric acid) from WPA produced by decomposing phosphate rock with nitric acid has been investigated using four different extractants (tributyl phosphate, methyl isobutyl ketone, n-octanol and tri-n-octyl amine) in kerosene. The results show that tri-n-octyl amine (TOA) is an effective extractant for the extraction of nitric acid from the WPA. Optimum conditions for the extraction process have also been determined. The results indicate that TOA has a good ability to extract nitric acid, while only a small amount of phosphoric acid is co-extracted. TOA can be used as an effective extractant to separate nitric acid from the WPA to produce phosphoric acid. The effect of the main impurities existing in the WPA produced by nitric acid dissolution of phosphate ore (Ca2+, Fe3+, Al3+, Mg2+ and F-) has also been studied. The results show that the impurities have a negative effect on the extraction of nitric acid or phosphoric acid and can be partly removed in the extraction. In addition, the number of theoretical stages for extracting 99.9 % of the nitric acid is calculated by the McCabe-Thiele method.