Process for the purification of an impure phosphoric acid

Claim 2

A process for the purification of wet process phosphoric acid containing sulfate ion in an amount by weight such that the ratio SO 4 /P 2 O 5 is greater than 50 ppm, comprising countercurrently liquid-liquid extracting an aqueous solution of said wet process phosphoric acid with a water-insoluble organic solvent; next, phase separating and countercurrently washing and neutralizing the organic phase effluent of said countercurrent liquid-liquid extraction, in at least two-stages, with an aqueous wash solution of a pH increasing amount of an alkali metal or ammonium compound; and thence recovering from said washed organic phase effluent purified phosphoric acid having a content of SO 4 to P 2 O 5 of less than 50 ppm.

Claim 3

The process as defined by claim 1, further comprising re-extracting, with water, said washed organic phase effluent.

Claim 4

The process as defined by claim 1, wherein said aqueous solution of wet process phosphoric acid subjected to liquid-liquid extraction comprises aqueous phase recycle from said countercurrent washing.

Claim 5

The process as defined by claim 3, further comprising separately introducing concentrated sulfuric acid to said wet process phosphoric acid being subjected to the countercurrent liquid-liquid extraction.

Claim 6

The process as defined by claim 2, wherein said aqueous solution of wet process phosphoric acid subjected to liquid-liquid extraction comprises aqueous phase recycle from said countercurrent washing.

Claim 7

The process as defined by claim 5, further comprising recycling re-extracted, water-insoluble organic solvent effluent to said countercurrent liquid-liquid extraction.

Claim 8

The process as defined by claim 6, said re-extraction being in at least two-stages.

Claim 9

The process as defined by claim 7, further comprising recovering depleted wet process phosphoric acid from said countercurrent liquid-liquid extraction.

Claim 10

The process as defined by claim 5, wherein said alkali metal or ammonium compound is an acid compound selected from the group consisting of the alkali metal and ammonium salts.

Claim 11

The process as defined by claim 9, said compound being a sodium compound.

Claim 12

The process as defined by claim 9, said compound being monosodium phosphate.

Claim 13

The process as defined by claim 5, said compound being a basic compound selected from the group consisting of the alkali metal or ammonium hydroxides, carbonates and phosphates.

Claim 14

The process as defined by claim 5, said aqueous wash liquid being acidic.

Claim 15

The process as defined by claim 5, said aqueous wash liquid being basic.

Claim 16

The process as defined by claim 5, said organic phase comprising at least one water-insoluble phosphoric acid extraction solvent.

Claim 17

The process as defined by claim 15, said extraction solvent being an alkyl phosphate.

Claim 18

The process as defined by claim 15, said extraction solvent being a C 2 -C 8 aliphatic alcohol.

Claim 19

The process as defined by claim 5, said washing comprising from three- to fifteen-stages.

Claim 20

The process as defined by claim 5, said washing being effected at a temperature of from 20° C. to 80° C.

Claim 21

The process as defined by claim 5, said water of re-extraction comprising alkali metal or ammonium ions.

Claim 22

The process as defined by claim 16, said organic phase comprising tributyl phosphate.

Claim 23

A process for the purification of wet process phosphoric acid containing sulfate ion in an amount by weight such that the ratio SO 4 /P 2 O 5 is greater than 50 ppm, consisting essentially of countercurrently liquid-liquid extracting an aqueous solution of 20-60% by weight P 2 O 5 wet process phosphoric acid with a water-insoluble organic solvent; next, phase separating and countercurrently washing and neutralizing the organic phase effluent of said countercurrent liquid-liquid extraction, in at least two-stages, with an aqueous wash solution of a pH increasing amount of an alkali metal or ammonium compound; and thence recovering from said washed organic phase effluent purified phosphoric acid having a content of SO 4 to P 2 O 5 of less than 50 ppm.

Claim 24

A process for the purification of wet process phosphoric acid containing sulfate ion in an amount by weight such that the ratio SO 4 /P 2 O 5 is greater than 50 ppm, consisting essentially of countercurrently liquid-liquid extracting an aqueous solution of 20-60% by weight P 2 O 5 wet process phosphoric acid with a water-insoluble organic solvent; next, phase separating and countercurrently washing and neutralizing the organic phase effluent of said countercurrent liquid-liquid extraction, in at least two-stages, with an aqueous wash solution of a pH increasing amount of an alkali metal or ammonium compound; and thence recovering from said washed organic phase effluent purified phosphoric acid having a content of SO 4 to P 2 O 5 of less than 50 ppm.