Purification of phosphoric acid rich streams

摘要

The invention relates to a method for the purification or recovery of orthophosphoric acid rich streams by suspension-based melt crystallization. The orthophosphoric acid is crystallized as the hemi-hydrate form and subsequent separation of such crystals in a wash-column produce a high purity acid/water solution that has been depleted of most of the metals and impurities other than water, thereby separating an orthophosphoric acid rich feed liquor into an ultra-pure orthophosphoric acid hemi-hydrate and a mother liquor containing almost all impurities originally present in the feed. The orthophosphoric acid rich feed liquor typically contains no more than 15 wt % water and 1 wt % other impurities. Individual metal ion composition in the purified orthophosphoric acid product is in the range of 100 to 1000 ppb (parts per billion= 1/1000 ppm) of each metal ion. The metal ion composition of the resulting purified product is thus typically below the detection limit of typical analysis equipment.