Defluorination of wet process phosphoric acid

Claim 2

A process according to claim 2 wherein the silica is selected from the group consisting of diatomaceous silica having a surface area of from about 15 to about 30 sq.m./gram and spray dried silica gel having a surface area of from about 320 to about 500 sq.m./gram.

Claim 3

A process according to claim 1 wherein the volatilizing of the SiF4 is effected by air sparging employing from about 0.5 to about 10 cubic feet of air per minute per ton of heated mixture.

Claim 4

A process according to claim 1 wherein the volatilizing of the SiF4 is effected by air sparging employing from about 1 to about 5 cubic feet of air per minute per ton of heated mixture.

Claim 5

A process according to claim 5 wherein about 1.1 pound of silica is employed per pound of fluorine contained in said heated mixture.

Claim 6

A process according to claim 6 wherein the silica is selected from the group consisting of diatomaceous silica or spray dried silica gel wherein the surface area of the silica is in the range of between 10 and 40 sq.m./gram.

Claim 7

A process according to claim 1 wherein the volatilizing of the SiF4 is effected by a combination of acid spraying and air sparging.

Claim 8

A process according to claim 1 wherein the process is continuous.

Claim 9

A process for the defluorination of wet process phosphoric acid containing from about 0.3 percent to about 3 percent by weight of fluorine as aluminum fluoride complexes, from about 0.8 percent by weight to about 2.2 percent by weight of dissolved aluminum and a P2O5 percent by weight of from about 45 percent to about 62 percent comprising the steps of: a. admixing said wet process acid with an amount of silica at least about stoichiometrically equivalent to the fluorine to be removed therefrom; b. heating the mixture at a temperature in the range of from about 75* C. to about 105* C. but below the boiling point of said mixture; c. volatilizing the SiF4 from the heated mixture into an inert gas effluenT stream by intimately contacting said heated mixture with an inert gas wherein the gas-mixture interface is sufficient to establish a stripping ratio of the SiF4 above about 1.5 and maintain the dissolved silicon concentration below about 0.05 percent by weight weight substantially throughout the defluorination; d. maintaining the temperature of said effluent stream above its dew point; and e. removing said effluent stream from the presence of the acid mixture.

Claim 10

A process according to claim 10 wherein the F/Si weight ratio is maintained above about 8 substantially throughout the defluorination.