Method of removing suspended solids from phosphoric acid

Claim 2

A process for removing particulate impurities from phosphoric acid comprising the steps of: (a) forming a filter cake comprising diatomite on a surface of a porous support member; (b) maintaining phosphoric acid containing particulate impurities at a temperature no greater than about 77° C.; (c) filtering said phosphoric acid through the formed filter cake, whereby said particulate impurities and some of the phosphate values in said phosphoric acid are retained by an outer portion of the filter cake; (d) removing the impurity-containing outer portion of the filter cake to expose a fresh surface of the filter cake to the phosphoric acid which is being filtered; (e) forming an aqueous slurry of said removed outer portion of said filter cake, said slurry comprising a liquid phase containing phosphate values and a solid phase comprising diatomite and particulate impurities; and (f) separating the liquid phase from the solid phase to recover a liquid containing a major portion of the phosphate values retained by the outer portion of the filter cake.

Claim 3

In the wet process for manufacturing phosphoric acid by acidulation of phosphorus-bearing rock with sulfuric acid to precipitate calcium sulfate and to release crude phosphoric acid containing solids-forming impurities and thereafter concentrating said crude impurity-containing phosphoric acid to produce a concentrated phosphoric acid containing suspended particles formed from said solids-forming impurities, the improvement comprising the steps of: (a) forming a filter element consisting essentially of a diatomite filter cake precoating overlying an outer surface of a porous support member; (b) contacting at least a portion of an outer surface of said filter cake with said concentrated phosphoric acid at a temperature in the range of about 57° C. to about 77° C., while maintaining reduced pressure on an inner surface of said porous support member to filter said concentrated phosphoric acid through said filter cake to remove at least a portion of the suspended particles from said concentrated phosphoric acid, said removed particles and a portion of the phosphate values from the concentrated phosphoric acid being retained in the contacted outer surface portion of said filter cake; (c) collecting said acid after filtration; (d) removing the contacted portion of said outer surface of said filter cake containing said retained solids, after each said contact thereof by said acid, to present relatively fresh outer filter cake surface for subsequent concentrated phosphoric acid contact; (e) forming an aqueous slurry of said removed portion; and (f) introducing said slurry into a phosphoric acid manufacturing process.

Claim 4

In the wet process for manufacturing phosphoric acid by acidulation of phosphorus-bearing rock with sulfuric acid to precipitate calcium sulfate and to release crude phosphoric acid containing solids-forming impurities and thereafter concentrating said crude impurity-containing phosphoric acid to produce a concentrated phosphoric acid containing suspended particles formed from said solids-forming impurities, the improvement comprising the steps of: (a) forming a filter element consisting essentially of a diatomite filter cake precoating overlying an outer surface of a porous support member; (b) contacting at least a portion of an outer surface of said filter cake with said concentrated phosphoric acid at a temperature in the range of about 57° C. to about 77° C., while maintaining reduced pressure on an inner surface of said porous support member to filter said concentrated phosphoric acid through said filter cake to remove at least a portion of the suspended particles from said concentrated phosphoric acid, said removed particles and a portion of the phosphate values from the concentrated phosphoric acid being retained in the contacted outer surface portion of said filter cake; (c) collecting said acid after filtration; (d) removing the contacted portion of said outer surface of said filter cake containing said retained solids, after each said contact thereof by said acid, to present relatively fresh outer filter cake surface for subsequent concentrated phosphoric acid contact; (e) forming an aqueous slurry of said removed portion; and (f) introducing said slurry into a phosphoric acid manufacturing process.

Claim 5

A process for removing impurities from wet process phosphoric acid comprising the steps of: (a) maintaining wet-process produced phosphoric acid containing particulate impurities at a temperature of from about 57° C. to about 77° C.; (b) filtering said phosphoric acid through a filter cake to remove particulate impurities from said phosphoric acid, at least a portion of said filter cake retaining phosphate values; (c) forming an aqueous slurry comprising removed particulate impurities and a portion of said filter cake retaining phosphate values; and (d) reprocessing said aqueous slurry by separating liquid from said slurry to recover an aqueous phase containing a major portion of the phosphate values retained by the filter cake.

Claim 6

A process for removing impurities from wet process phosphoric acid comprising the steps of: (a) maintaining wet-process produced phosphoric acid containing particulate impurities at a temperature of from about 57° C. to about 77° C.; (b) filtering said phosphoric acid through a filter cake to remove particulate impurities from said phosphoric acid, at least a portion of said filter cake retaining phosphate values; (c) forming an aqueous slurry comprising removed particulate impurities and a portion of said filter cake retaining phosphate values; and (d) reprocessing said aqueous slurry by separating liquid from said slurry to recover an aqueous phase containing a major portion of the phosphate values retained by the filter cake.

Claim 7

The process of claim 1 wherein said diatomite filter cake contains cellulose fibers.

Claim 8

The process of claim 2 wherein said concentrated phosphoric acid analyzes about 50% P 2 O 5 by weight.

Claim 9

The process of claim 2 wherein said phosphoric acid was produced by the wet process.

Claim 10

The process of claim 2 wherein said filter aid comprises diatomite.

Claim 11

The process of claim 2 wherein in step (b) said concentrated phosphoric acid is maintained within said temperature range for a period of at least 24 hours.

Claim 12

The process of claim 9 wherein said period is in the range of 24 to 48 hours.

Claim 13

The process according to claim 3 wherein said aqueous phase is used as a filter wash in a phosphoric acid manufacturing process.

Claim 14

The process according to claim 3 wherein said aqueous phase is used in the dissolution of phosphate rock in a phosphoric acid manufacturing process.