| 摘要 |
A method for purifying or recovering phosphoric acid rich streams is provided to produce a product with high purity which is required for various applications, e.g., in the electronics industry, and a method for purifying or recovering phosphoric acid rich streams, which does not require frequent repetition of multiple batch wise process steps, is provided. A method for recovering or ultra-purifying orthophosphoric acid rich feed streams without solvent crystallization or without requiring multiple discontinuous layer melt crystallization steps comprises the steps of: a) cooling the orthophosphoric acid rich stream below its freezing point to form hemi-hydrate crystals, resulting in the formation of a mixed phase slurry of mother liquid and suspended crystals; b) cooling the slurry such that the slurry has a volume with a crystal content of 15 to 50% by weight of the hemi-hydrate crystal, wherein the available surface for crystal growth is not less than 5,000 m^2 per m^3 of crystallizer volume; c) holding the slurry in a mixing tank such that a crystal residence time is preferably from 15 minutes to 4 hours, more preferably from 30 minutes to 2 hours and most preferably from 30 minutes to 1 hour; d) separating the crystals from the mother liquid in a wash column; e) heating a portion of the hemi-hydrate crystals until the hemi-hydrate crystals are essentially all melted to form a liquid of the purified acid and water; f) washing the hemi-hydrate crystals in the wash column, wherein the crystals are washed in the counter-current flow direction by contact with the purified melt of the crystals and recrystallized on the supercooled crystals although there is no wash loss; g) discharging the melted hemi-hydrate crystals as purified orthophosphoric acid and water solution; and h) discharging essentially all other impurities in the separated mother liquid.
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