Process for the production of titanium dioxide

Abstract

It is disclosed a process for the production of titanium dioxide comprising the following steps: (a) a titanium ore containing iron, preferably ilmenite, is reacted with an aqueous NH 4 F solution; (b) the aqueous suspension thus obtained is filtered with consequent separation of a sludge fraction, which contains ammonium fluoroferrates, and a filtrate fraction, which contains ammonium fluorotitanates; (c) the filtrate fraction thus obtained is subjected to an hydrolysis reaction; (d) the thus-obtained solid component is subjected to a thermal hydrolysis reaction. The plant and the reactors for performing the above process are also disclosed.

1 . A process for the production of titanium dioxide comprising the following steps: 
 (a) a titanium ore containing iron is reacted with an aqueous NH 4 F solution;    (b) the aqueous suspension thus obtained is filtered with consequent separation of a sludge fraction and a filtrate fraction;    (c) the filtrate fraction thus obtained is subjected to an hydrolysis reaction;    (d) the thus-obtained solid component is subjected to a thermal hydrolysis reaction.    
   
   
       2 . A process according to  claim 1 , wherein the sludge fraction of step (b) contains ammonium fluoroferrates.  
   
   
       3 . A process according to  claim 1 , wherein the filtrate fraction of step (b) contains ammonium fluorotitanates.  
   
   
       4 . A process according to  claim 1 , wherein step (a) is performed at 100-120° C.  
   
   
       5 . A process according to  claim 1 , wherein step (a) is performed at a pressure of about 1-2 bar.  
   
   
       6 . A process according to  claim 1 , wherein step (a) is performed at a pH of about 6.5-7.0.  
   
   
       7 . A process according to  claim 1 , wherein the aqueous NH 4 F solution has a concentration of 30-60% by weight.  
   
   
       8 . A process according to  claim 1 , wherein the aqueous NH 4 F solution has a concentration of about 45% by weight.  
   
   
       9 . A process according to  claim 1 , wherein the thermal hydrolysis reaction (d) is performed in two reactors.  
   
   
       10 . A process according to  claim 9 , wherein the first reactor is maintained at a temperature of up to 350° C.  
   
   
       11 . A process according to  claim 9 , wherein the first reactor is maintained at a temperature of up to 300-350° C.  
   
   
       12 . A process according to  claim 9 , wherein the second reactor is maintained at a temperature of up to 900° C.  
   
   
       13 . A process according to  claim 9 , wherein the second reactor is maintained at a temperature of up to 800-900° C.  
   
   
       14 . A process according to  claim 9 , wherein the body of the first and/or second reactor is made of a chromium-nickel alloy.  
   
   
       15 . A process according to  claim 9 , wherein the internal surface of the first reactor is made of magnesium or a graphite-reinforced polymer or vitreous carbon.  
   
   
       16 . A process according to  claim 9 , wherein the internal surface of the second reactor is made of silica.  
   
   
       17 . A process according to  claim 1 , wherein the aqueous dispersion obtained from the hydrolysis reaction (c) is filtered before the thermal hydrolysis reaction (d).  
   
   
       18 . A process according to  claim 1 , wherein the sludge fraction of step (b) is subjected to a thermal hydrolysis reaction.  
   
   
       19 . A process according to  claim 18 , wherein said thermal hydrolysis is performed at a temperature of up to 300-350° C.  
   
   
       20 . A process according to  claim 18 , wherein the sludge fraction of step (b) is dehydrated and dried before being subjected to said thermal hydrolysis.  
   
   
       21 . A process according to  claim 1 , wherein the titanium ore containing iron is ilmenite.