Patent ID: 8034312
Filing Date: 2011-10-11
Classification: C01B

Abstract:
1. A method for the recovery or ultra-purification of orthophosphoric acid rich feed streams in the absence of solvent crystallization and avoiding multiple discontinuous layer melt crystallization steps, said method comprising the steps of: a) Cooling the orthophosphoric acid rich stream below its freezing point to form hemi-hydrate crystals, resulting in a mixed phase slurry of mother liquor and suspended crystals, b) Cooling said slurry to create a volume with a crystal content of between 15% and 50% by weight of the hemi-hydrate crystal characterized in that the available surface for crystal growth is not less than 5,000 m c) Holding said slurry in a mixing tank to create a crystal residence time between 15 minutes and 4 hours, d) Separating said crystals from the mother liquid in a wash column, e) Heating a portion of the hemi-hydrate crystals until they are essentially all melted to form a liquid of purified acid and water, f) Washing the hemi-hydrate crystals in the wash column, characterized in that the crystals are counter-currently washed by contact with the purified melt of said crystals wherein no wash is lost but is recrystallized on supercooled crystals, 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 liquor.