Process for manufacturing titanium dioxide

A continuous process for producing titanium dioxide pigment which comprises:

• (1) reacting (a) ilmenite, in an amount between 10% and 400% in excess of the stoichiometric amount of ilmenite necessary to react with sulfuric acid to provide titanyl sulphate and (b) dilute sulfuric acid solution having a concentration between about 25% and about 60% by weight, based upon the total weight of said solution, at a temperature below about 140.degree. C. in the presence of a reducing agent which effects the reduction of ferric iron to ferrous iron;
• (2) cooling the resulting reaction mixture from (1) to a temperature below about 100.degree. C. in a second reaction vessel;
• (3) separating unreacted ilmenite from the reaction mixture of (2) to provide a solution of iron sulphate and titanyl sulphate and recycling said unreacted ilmenite to (1);
• (4) removing iron sulphate from said solution of iron sulphate and titanyl sulphate to provide a solution of titanyl sulphate;
• (5) hydrolyzing said titanyl sulphate solution from (4) to provide a titanium dioxide hydrate, and recycling spent sulfuric acid to (1);
• (6) calcining said titanium dioxide hydrate to provide titanium dioxide, and
• (7) recovering titanium dioxide.

A continuous process for producing titanium dioxide pigment which comprises:

• (1) reacting (a) ilmenite, in an amount between 10% and 400% in excess of the stoichiometric amount of ilmenite necessary to react with sulfuric acid to provide titanyl sulphate, and (b) dilute sulfuric acid solution having a concentration between about 25% and about 60% by weight, based upon the total weight of said solution, in a first reaction vessel at a temperature below about 140.degree. C. in the presence of a reducing agent which effects the reduction of ferric iron to ferrous iron, to provide a reaction solution having a ratio of active acid to titanium dioxide of about 3.0;
• (2) continuously transporting said reaction solution from said first reaction vessel to a second reaction vessel, and recycling a portion of unreacted ilmenite to (1);
• (3) continuing said reaction of ilmenite and dilute sulfuric acid in said second reaction vessel at a temperature below about 100.degree. C. to provide a reaction solution having a ratio of active acid to titanium dioxide of about 2.0;
• (4) separating unreacted ilmenite from the reaction mixture of (3) to provide a solution of iron sulphate and titanyl sulphate, and recycling said unreacted ilmenite to (3) or (1);
• (5) cooling the reaction solution of (4) to crystallize iron sulphate;
• (6) filtering the reaction mixture of (5) to remove iron sulphate crystals and provide a solution of titanyl sulphate
• (7) hydrolyzing said solution of titanyl sulphate from (6) to provide a titanium dioxide hydrate, and recycling spent sulfuric acid to (1);
• (8) calcining said titanium dioxide hydrate from (7) to provide titanium dioxide, and
• (9) recovering titanium dioxide.

A continuous process for producing titanium dioxide pigment which comprises:

• (1) reacting (a) ilmenite, in an amount between 10% and 400%, in excess of the stoichiometric amount of ilmenite necessary to react with sulfuric acid to provide titanyl sulphate, and (b) dilute sulfuric acid solution having a concentration between about 25% and about 60% by weight, based upon the total weight of said solution, in a first reaction vessel at a temperature below about 140.degree. C. in the presence of a reducing agent which effects the reduction of ferric iron to ferrous iron, to provide a reaction solution having a ratio of active acid to titanium dioxide of between about 3.0 and about 7.0;
• (2) continuously transporting said reaction solution from said first reaction vessel to a second reaction vessel, and recycling a portion of unreacted ilmenite to (1);
• (3) continuing said reaction of ilmenite and dilute sulfuric acid in said second reaction vessel at a temperature of about 100.degree. C. to provide a reaction solution having a ratio of active acid to titanium dioxide of between about 2.4 and and about 3.5;
• (4) continuously transporting said reaction solution from said second reaction vessel to a third reaction vessel and recycling a portion of unreacted ilmenite to (3);
• (5) continuing said reaction of ilmenite and dilute sulfuric acid in said third reaction vessel at a temperature of about 80.degree. C. to provide a reaction solution having a ratio of active acid to titanium dioxide of about 2.0;
• (6) separating unreacted ilmenite from the reaction mixture of (5) to provide a solution of iron sulphate and titanyl sulphate, and recycling said unreacted ilmenite to (5) or (1);
• (7) cooling the reaction solution of (5) to crystallize iron sulphate;
• (8) filtering the reaction mixture of (7) to remove iron sulphate crystals and provide a solution of titanyl sulphate;
• (9) hydrolyzing said solution of titanyl sulphate from (8) to provide a titanium dioxide hydrate and recycling spent sulfuric acid to (1);
• (10) calcining said titanium dioxide hydrate from (9) to provide titanium dioxide, and
• (11) recovering titanium dioxide.