Process for the manufacture of wet process phosphoric acid using wet-grinding of the phosphate rock feed

Claim 1

A method of manufacturing wet process phosphoric acid from phosphate rock, comprising the steps of i. grinding the phosphate rock in a water slurry sufficiently that the phosphate rock will pass a 30 mesh (Tyler) screen, said slurry containing at least about 20 weight percent water, and said slurry being formed with water containing no more than 2 percent P 2 O 5 ; ii. passing the slurry of ground rock to an attack tank and therein contacting and reacting the slurry with diluted sulfuric acid obtained from step (vi) herein to yield a product slurry of crystalline hydrated calcium sulfate in phosphoric acid having a P 2 O 5 value of at least about 25 weight percent, said slurry providing about 15 to 35 weight percent of the water present in said attack tank; iii. removing said product slurry from the attack tank; iv. subjecting said product slurry to a separation step whereby the crystalline hydrated calcium sulfate is separated from the phosphoric acid; v. washing the separated calcium sulfate with water and obtaining spent wash water having a P 2 O 5 value of about 15 to 25 weight percent; vi. mixing the spent calcium sulfate wash water with concentrated sulfuric acid having a concentration of at least about 90 percent to obtain diluted sulfuric acid; and vii. passing the diluted sulfuric acid to step (ii) above to supply about 60 to 85% of the total amount of water in the attack tank, said concentrated sulfuric acid supplying up to about 5 percent of the water present in said attack tank.

Claim 2

A method of manufacturing wet process phosphoric acid from phosphate rock, comprising the steps of i. grinding the phosphate rock in a water slurry sufficiently that the phosphate rock will pass a 30 mesh (Tyler) screen, said slurry containing at least about 20 weight percent water, and said slurry being formed with water containing no more than 2 percent P 2 O 5 ; ii. passing the slurry of ground rock to an attack tank and therein contacting and reacting the slurry with diluted sulfuric acid obtained from step (vi) herein to yield a product slurry of crystalline hydrated calcium sulfate in phosphoric acid having a P 2 O 5 value of at least about 25 weight percent, said slurry providing about 15 to 35 weight percent of the water present in said attack tank; iii. removing said product slurry from the attack tank; iv. subjecting said product slurry to a separation step whereby the crystalline hydrated calcium sulfate is separated from the phosphoric acid; v. washing the separated calcium sulfate with water and obtaining spent wash water having a P 2 O 5 value of about 15 to 25 weight percent; vi. mixing the spent calcium sulfate wash water with concentrated sulfuric acid having a concentration of at least about 90 percent to obtain diluted sulfuric acid; and vii. passing the diluted sulfuric acid to step (ii) above to supply about 60 to 85% of the total amount of water in the attack tank, said concentrated sulfuric acid supplying up to about 5 percent of the water present in said attack tank.