process for purification by solvent extraction of phosphoric acid obtained by a wet process.

摘要

A wet process phosphoric acid obtained by an solvent extraction method with n-butanol and/or isobutanol comprises (a) feeding a wet process phosphoric acid having a concentration of P2O5 of higher than 35 wt. % into an extraction battery; (b) adding sulfuric acid into a stage in fifth or higher stage from the step of discharging an extracted solution and in second or higher stage from the step of discharging raffinate in the extraction battery at a gram equivalent ratio given by subtracting the amount of sulfuric acid in the wet process phosphoric acid fed into the extraction battery from 1.2 to 2.0 times of the sum of total cation impurities in the wet process phosphoric acid fed into the extraction battery and total components of sodium, potassium and magnesium added to the purification battery; (c) discharging said extracted solution having a concentration of H3PO4 of 130 to 180 g./liter from said extraction battery; (d) adding at least one of the compounds of sodium, potassium and magnesium in second or higher stage from the step of discharging the solvent phase and in second or higher stage from the step of discharging the aqueous phase in the purification battery to give more than 0.4 equivalent per liter of the concentration of sodium, potassium and magnesium in the aqueous phase in the stage where at least one of alkali metal and magnesium compounds is added in the same battery.