Production of titania

Abstract

A process for producing titania from a solid, iron-containing titaniferous material (such as ilmenite) is disclosed. The process includes a first step of treating iron-containing titaniferous material under conditions that reduce ferric ions to ferrous ions in the titaniferous material. Thereafter the process include steps of leaching treated titaniferous material and forming a leach liquor that includes an acidic solution of titanyl sulfate and iron sulfate and recovering titania from the leach liquor.

1 . A process for producing titania from a solid, iron-containing titaniferous material (such as ilmenite) which includes the steps of: 
 (a) treating iron-containing titaniferous material under conditions that reduce ferric ions to ferrous ions in the titaniferous material, the conditions including contacting the titaniferous material with a reducing gas;    (b) leaching treated titaniferous material and forming a leach liquor that includes an acidic solution of titanyl sulfate and iron sulfate;    (c) recovering titania from the leach liquor.    
   
   
       2 . The process defined in  claim 1  wherein step (a) comprises treating titaniferous material under conditions that result in ferrous ions being a predominant form of iron in the titaniferous material.  
   
   
       3 . The process defined in  claim 1  wherein step (a) comprises treating titaniferous material under conditions that do not result in substantial formation of rutile that is unleachable under the conditions of leaching step (b).  
   
   
       4 . The process defined in  claim 1  wherein step (a) comprises treating titaniferous material under conditions so that there is either no metallic iron formed in the step or a selected relatively small amount of metallic iron formed in the step.  
   
   
       5 . The process defined in  claim 1  wherein step (a) comprises treating titaniferous material by contacting titaniferous material with the reducing gas in a fluidized bed.  
   
   
       6 . The process defined in  claim 1  wherein the reducing gas comprises any suitable gas, such as hydrogen, carbon monoxide, and mixtures thereof.  
   
   
       7 . The process defined in  claim 1  wherein the reducing gas is a mixture of (a) hydrogen and/or carbon monoxide and/or methane and (b) another suitable gas such as an inert gas and/or carbon dioxide.  
   
   
       8 . The process defined in  claim 7  wherein the inert gas is nitrogen.  
   
   
       9 . The process defined in  claim 7  wherein, in a situation in which the reducing gas comprises hydrogen and the inert gas comprises nitrogen, the hydrogen comprises up to 25% by volume of the reducing gas.  
   
   
       10 . The process defined in  claim 1  wherein, in a situation in which the reducing gas comprises hydrogen, the temperature of the reducing gas is less than 700° C. to avoid substantial formation of rutile that is unleachable under the conditions of leaching step (b).  
   
   
       11 . The process defined in  claim 1  wherein, in a situation in which the reducing gas comprises hydrogen, the temperature of the reducing gas is 450-550° C.  
   
   
       12 . The process defined in  claim 7  wherein, in a situation in which the reducing gas comprises carbon monoxide and the other gas comprises carbon dioxide, the carbon monoxide comprises up to 60% by volume of the reducing gas.  
   
   
       13 . The process defined in  claim 7  wherein, in a situation in which the reducing gas comprises carbon monoxide and the inert gas comprises nitrogen, the temperature of the reducing gas is less than 700° C.  
   
   
       14 . The process defined in  claim 7  wherein, in a situation in which the reducing gas comprises carbon monoxide and the inert gas comprises nitrogen, the temperature of the gas is 600° C.  
   
   
       15 . The process defined in  claim 1  wherein the average contact time of the titaniferous material and the reducing gas in step (a) is less than 120 minutes.  
   
   
       16 . The process defined in  claim 1  wherein the leaching step (b) comprises a multiple leaching step involving (i) a first step of leaching the titaniferous material with the leach liquor and forming a process solution that includes an acidic solution of titanyl sulfate; (ii) separating the process solution and a residual solid phase; (iii) leaching the residual solid phase in a subsequent leach step with a leach liquor and forming a further process solution that includes an acidic solution of titanyl sulfate and iron sulfate; (iv) separating the process solution and a residual solid phase; and (v) supplying the separated process solution to the first leach step and/or mixing the separated process solution with the process solution from the first leach step for subsequent processing in reducing step (c).  
   
   
       17 . The process defined in  claim 1  wherein the leaching step (b) includes selecting and/or controlling the leaching conditions to avoid undesirable amounts of premature hydrolysis and undesirable amounts of premature precipitation.  
   
   
       18 . The process defined in  claim 1  wherein the acid concentration in the leaching step (b) is at least 350 g/l sulfuric acid throughout the leaching step when operating at a leach temperature in the range of from 95° C. to the boiling point in order to avoid premature hydrolysis.  
   
   
       19 . The process defined in  claim 1  wherein the acid concentration at the end of the leaching step (b) is less than 450 g/l when operating at a leach temperature in the range from 95° C. to the boiling point in order to avoid an undesirable amount of premature precipitation of titanyl sulfate.  
   
   
       20 . The process defined in  claim 1  wherein the acid concentration at the start of the leaching step (b) is less than 700 g/l.  
   
   
       21 . The process defined in  claim 1  wherein step (c) of recovering titania from the leach liquor comprises the steps of (i) separating iron sulfate from the leach liquor, (ii) separating titanyl sulfate from the leach liquor either after or before step (i), and (iii) recovering titania from the titanyl sulfate.  
   
   
       22 . The process defined in  claim 21  wherein step (ii) of separating titanyl sulfate from the leach liquor comprises solvent extraction of titanyl sulfate from the leach liquor.  
   
   
       23 . The process defined in  claim 21  wherein step (ii) of separating titanyl sulfate from the leach liquor comprises precipitating titanyl sulfate from the leach liquor.  
   
   
       24 . The process defined in  claim 1  wherein the leaching step (b) is in accordance with a standard sulfate process which includes a 2-stage step with a first stage involving solid state sulfation of pre-treated titaniferous material from step (a) with concentrated sulfuric acid and a second stage involving dissolving the sulfated product in water/dilute acid and forming an acidic solution of titanyl sulfate and iron sulfate.