Process for production of pigmentary titanium dioxide

Claim 2

A PROCESS FOR THE PRODUCTION OF PIGMENTARY TITANIUM DIOXIDE COMPRISING: CONVERTING AN IRON-CONTAINING TITANIFEROUS MATERIAL TO TITANIUM TETRAFLOURIDE, REACTING THE TITANIUM TETRAFLOURIDE WITH SULFURIC ACID TO FORM TITANIUM SULFATE SOLUTION AND HYDROGEN FLUORIDE, REMOVING HYDROGREN FLUORIDE PRIOR TO HYDROLYSIS OF THE TITANIUM SULFATE, FORMING AN AQUEOUS ACIDIC SOLUTION OF TITAIUM SULFATE, SUBJECTING THE AQUEOUS TITANIUM SULFATE SOLUTION TO THERMAL HYDROLYSIS TO PRECIPATE HYDROUS TITAIUM DIOXIDE, AND THEREAFTER CALCINING THE HYDROUS TITANIUM DIOXIDE.

Claim 3

A process as claimed in claim 1 wherein the titanium tetrafluoride is formed by the reaction of ferric fluoride with ilmenite.

Claim 4

A process as claimed in claim 1 wherein the titanium tetrafluoride is reacted with aqueous sulphuric acid having a concentration in the range 20 to 95%.

Claim 5

A process as claimed in claim 3 wherein the aqueous sulphuric acid has a concentration in the range 60 to 90%.

Claim 6

A process as claimed in claim 1 wherein the ratio of titanium (expressed as TiO2) to sulphuric acid is in the range 1:1 to 1:3.

Claim 7

A process as claimed in claim 5 wherein the ratio of titanium to sulphuric acid is in the range 1:1.6 to 1:2.0.

Claim 8

A process as claimed in claim 1 wherein titanium tetrafluoride and sulphuric acid are reacted together at a temperature in the range 70* to 300*C.

Claim 9

A process as claimed in claim 7 wherein titanium tetrafluoride and sulphuric acid are reacted together at a temperature in the range 150* to 250*C.

Claim 10

A process as claimed in claim 1 wherein said aqueous acidic titanium sulphate solution contains titanium (expressed as TiO2) in a concentration in the range 150 to 350 gram/litre and sulphuric acid in the range 300 to 600 gram/litre.

Claim 11

A process as claimed in claim 9 wherein said aqueous acidic titanium sulphate solution contains titanium (expressed as TiO2) in the range 200 to 300 gram/litre and sulphuric acid in the range 350 to 550 gram/litre.

Claim 12

A process as claimed in claim 1 wherein said titanium sulphate solution is heated and fluoride is removed from said titanium sulphate by passing steam through the heated solution.

Claim 13

A process as claimed in claim 11 wherein the acid to titanium ratio of the solution is in the range 1 to 3.

Claim 14

A process as claimed in claim 12 wherein the ratio is in the range 1.6 to 2.

Claim 15

A process as claimed in claim 11 wherein the solution is heated to a temperature in the range 110* to 140*C.

Claim 16

A process as claimed in claim 11 wherein the steam is at a temperature in the range 150* to 220*C.

Claim 17

A process as claimed in claim 11 wherein the titanium sulphate after fluoride removal contains less than 1% by weight of fluoride ions.

Claim 18

A process as claimed in claim 1 wherein the aqueous acidic solution of titanium sulphate is hydrolysed by heating to a temperature in the range 80* to 150*C. for a period of from 2 to 5 hours.

Claim 19

A process as claimed in claim 1 wherein the aqueous acidic solution of titanium sulphate is hydrolysed in the presence of from 0.2 to 5% of nuclei (expressed as TiO2) based on the amount of titanium (expressed as TiO2).

Claim 20

A process as claimed in claim 1 wherein the hydrogen fluoride liberated during the reaction between titanium tetrafluoride and sulphuric acid is reacted with ferric oxide to form ferric fluoride.

Claim 21

A process as claimed in claim 1 wherein the sulphuric acid in the mother liquor from the hydrolysis of the aqueous acidic titanium sulphate solution is purified by solvent extraction.

Claim 22

A process for the production of pigmentary titanium dioxide comprising: a. converting an iron-containing titaniferous material to titanium tetrafluoride; b. reacting the titanium tetrafluoride with aqueous sulphuric acid having a concentration of between 20 and 95% H2SO4 to form a solid hydrated titanium sulphate and aqueous hydrofluoriC acid; c. heating the mixture to a temperature in the range 110* to 140*C. to remove fluoride as gaseous hydrogen fluoride; d. dissolving said solid hydrated titanium sulphate in a solvent selected from the group consisting of water and dilute sulphuric acid to form an aqueous acidic titanium sulphate solution having a titanium content (expressed as TiO2) in the range 150 to 350 gram/litre; e. seeding the aqueous acidic titanium sulphate solution with anatase or rutile inducing nuclei; f. subjecting the seeded aqueous acidic titanium sulphate solution to thermal hydrolysis by heating said solution to a temperature in the range 80* to 150* C. until substantially all the titanium has been precipitated as hydrous titanium dioxide; and g. calcining said hydrous titanium dioxide.

Claim 23

A process for the production of pigmentary titanium dioxide comprising: a. converting an iron-containing titaniferous material to titanium tetrafluoride; b. reacting the titanium tetrafluoride with aqueous sulphuric acid having a concentration of between 20 and 95% H2SO4 to form a solid hydrated titanium sulphate and aqueous hydrofluoriC acid; c. heating the mixture to a temperature in the range 110* to 140*C. to remove fluoride as gaseous hydrogen fluoride; d. dissolving said solid hydrated titanium sulphate in a solvent selected from the group consisting of water and dilute sulphuric acid to form an aqueous acidic titanium sulphate solution having a titanium content (expressed as TiO2) in the range 150 to 350 gram/litre; e. seeding the aqueous acidic titanium sulphate solution with anatase or rutile inducing nuclei; f. subjecting the seeded aqueous acidic titanium sulphate solution to thermal hydrolysis by heating said solution to a temperature in the range 80* to 150* C. until substantially all the titanium has been precipitated as hydrous titanium dioxide; and g. calcining said hydrous titanium dioxide.

Claim 24

A process as claimed in claim 1 wherein the sulphuric acid in the mother liquor from the hydrolysis of the aqueous acidic titanium sulphate solution is purified by contact with an ion-exchange resin.