Method of producing low soda alumina, low soda alumina produced by the method and method of producing porcelain

Abstract

A method of producing alumina having a low soda content and excellent sintering properties includes the steps of adding a soda removal agent to alumina source material and calcining the alumina source material in a calciner ( 2 ), using a dust collector ( 5 ) to collect calcined alumina source material dust contained in the exhaust gas, discharging a portion of the collected dust out of the system, slurrying another portion of the collected dust in a slurrifier ( 10 ) while controlling slurry pH, washing and filtering the slurried dust and recirculating it back to the calciner, recirculating still another portion of the collected dust together with a mineralizing agent to the calciner, and removing the low soda alumina after the calcination.

1 . A method of producing a low-soda alumina comprising the steps of: 
 calcining an alumina source material in a calciner in the presence of a soda removal agent;    collecting in a dust collector a calcined alumina source material dust contained in an exhaust gas;    reducing a soda content in at least a portion of the collected alumina source material dust;    recirculating the alumina source material dust back to the calciner; and    extracting a low soda alumina calcined by the calciner.    
   
   
       2 . The method according to  claim 1 , wherein the step of reducing a soda content comprises slurrying the portion of the collected dust in a slurrifier while controlling slurry pH; and washing and filtering the slurried alumina source material dust.  
   
   
       3 . The method according to  claim 1 , further comprising the step of recirculating another portion of the collected dust to the calciner in its as-collected state.  
   
   
       4 . The method according to  claim 2 , further comprising the step of recirculating another portion of the collected dust to the calciner in its as-collected state.  
   
   
       5 . The method according to  claim 3 , further comprising the step of externally discharging still another portion of the collected dust.  
   
   
       6 . The method according to  claim 4 , further comprising the step of externally discharging still another portion of the collected dust.  
   
   
       7 . The method according to any one of  claims 1  to  6 , wherein the soda removal agent is added in an amount ratio that is 1 to 15 times a theoretical addition amount relative to a soda content of the alumina source material.  
   
   
       8 . The method according to any one of  claims 1  to  6 , wherein the soda removal agent comprises at least one compound selected from the group consisting of hydrochloric acid, ammonium chloride, magnesium chloride and chlorine-containing compounds.  
   
   
       9 . The method according to any of  claims 1  to  6 , wherein the soda removal agent is added to effect a counter-current reaction with the alumina source material.  
   
   
       10 . The method according to any one of claims  2 ,  4  and  6 . wherein the collected dust is slurried under a pH of 8 to 11, and washed and filtered to remove a soda content and mineralizing components from the dust.  
   
   
       11 . The method according to any one of claims  2 ,  4  and  6 , wherein a ratio between an amount (a) of the collected dust that is slurried, washed and filtered and an amount (b) of the dust that is collected and returned to the calciner without being slurried, washed and filtered is controlled.  
   
   
       12 . The method according to  claim 11 , wherein the amount (a) of the collected dust that is slurried, washed and filtered is all or a portion of the collected dust of amounts (a) and (b).  
   
   
       13 . The method according to any one of  claims 1  to  6 , wherein a content of mineralizing components in the collected dust that is recirculated to the calciner is controlled to have a fluorine-based compound content of 200 to 1,000 ppm, based on F.  
   
   
       14 . The method according to any one of  claims 1  to  6 , wherein the low soda alumina that is produced has an α-crystal diameter in a range of 0.4 to 10.0 μm.