Abstract:

Solvent extraction is an economical and effective method for the purification of wet process phosphoric acid（WPA）. WPA extraction proces was carried out using methyl isobutyl ketone（MIBK） as an extractant in a rotating disc column （RDC）.The effect of rotation speed and phase ratio on the extraction rate,the selectivity coefficient of impurities,and phos-phoric acid washing and stripping was studied.The results showed that the optimum extraction ratio（volume ratio of solvent to phosphoric acid） was 4,the stirring speed was 200~400 r/min,and the extraction rate of phosphoric acid was 85%.The stir-ring speed in the washing process was limited to 100 r/min.The appropriate amount of washing acid was 10%~15% of the vol-ume of solvent phase.The removal rates of Fe³⁺ and Mg²⁺ were more than 90%.The removal rate of Al³⁺ was more than 70% and the removal rate of SO₄^2- was 50%~60%.The stirring speed of stripping process was limited to 200 r/min,and the appropriate amount of stripping water was 9%~15% of the volume of solvent phase.MIBK had good removal effect on cations,but poor re-moval effect on anions.After purification by extraction,washing and stripping,the yield of phosphoric acid was 57.8%~70.3%. The content of Fe³⁺ in phosphoric acid could meet the standard of industrial phosphoric acid,but the content of sulfate could not meet the standard,so it needs to be further removed in combination with other methods.

Key words: wet process phosphoric acid, solvent extraction, methyl isobutyl ketone, rotating disc column