Method for treating tailings pond liquor

Abstract

A treatment process for processing raw liquor obtained from a tailings pond containing residue from an alumina production facility is disclosed where the raw liquor is first contacted with a gas containing carbon dioxide (CO 2 ) to neutralize the raw liquor and to precipitate aluminum hydroxide Al(OH) 3 . The aluminum hydroxide is separated from the neutralized liquor, which is rich in bicarbonates and then concentrated using membrane separation technology to form a NaHCO 3 (sodium bicarbonate) rich retentate. This NaHCO 3 rich retentate is then subjected to a regeneration process to recover NaOH for recycle to the alumina production facility.

1 . A process for treating raw tailings liquor collected from a red mud tailing pond discharged as waste from an alumina production facility comprising,
 (a) removing raw aqueous liquor from a red mud tailings pond;   (b) contacting the raw liquor with CO 2  gas to precipitate aluminum hydroxide (Al(OH) 3 ) to produce a neutralized liquor;   (c) separating the aluminum hydroxide from the neutralized liquor;   (d) concentrating the neutralized liquor using membrane separation to form a sodium bicarbonate (NaHCO3) rich retentate;   (e) regenerating the retentate to form a NaOH solution and a precipitated calcium carbonate (CaCO3); and   (f) separating the NaOH solution from the CaCO3.   
     
     
         2 . The process of  claim 1  further characterized in that flue gas from the aluminate production facility is used as a source of the CO 2  in step (b). 
     
     
         3 . The process of  claim 1  further characterized in that CO 2  gas is used to heat the neutralized liquor to about 120° F. or higher. 
     
     
         4 . The process of  claim 1  where the separated neutralized liquor from step (c) is heated to about 140° F. prior to the membrane separation. 
     
     
         5 . The process of  claim 1  where the aluminum hydroxide separated in step (c) is recycled back to the alumina production facility for processing into Al 2 O 3 . 
     
     
         6 . A process for treating tailings liquor from an alumina production facility comprising,
 a) removing raw liquor from a tailings pond having a pH greater than 10;   b) contacting the raw liquor with an industrial gas containing CO 2  in a quantity sufficient reduce the pH of the raw liquor to less than 8 causing precipitation of Al(OH)3 and forming a neutralized liquor;   c) separating the Al(OH)3 from the neutralized liquor;   d) filtering the neutralized liquor to remove suspended solids;   e) contacting the filtered neutralized liquor from step (d) using a reverse osmosis membrane to form a concentrated NaHCO3 rich retentate and a permeate;   f) contacting the retentate with lime in a crystallizer reactor to form a mixture of precipitated CaCO 3  and NaOH solution;   g) clarifying the mixture of step (f) to form a NaOH product solution;   h) recycling at least a portion of the NaOH product solution to the alumina production facility; and   i) recovering the CaCO 3 .   
     
     
         7 . The process of  claim 6  where the industrial gas stream and the raw liquor are contacted in a counter-current scrubber using a recycled slurry of precipitated Al(OH)3. 
     
     
         8 . The process of  claim 6  further comprising using the industrial gas stream to heat the neutralized liquor to at least 120° F. and maintaining the temperature of the aqueous liquor stream at or above 120° F. immediately prior to contact with the reverse osmosis membrane. 
     
     
         9 . The process of  claim 8  where the Al(OH) 3  separated in step (c) is filtered to form a cake of Al(OH) 3  and a filtrate solution. 
     
     
         10 . The process of  claim 9  where the Al(OH) 3  cake is recycled back to the alumina production facility for processing into Al 2 O 3  and the filtrate solution is added to the clarifying step along with the mixture from step (f). 
     
     
         11 . The process of  claim 6  where the filtering of the neutralized liquor stream in step (d) reduces the suspended solids level to a silt density index of <3. 
     
     
         12 . The process of  claim 6  where the filtered neutralized liquor is at a temperature below 120° F. and is heat exchanged to increase the temperature to at or above 120° F. 
     
     
         13 . The process of  claim 6  where a portion of the NaOH product solution is mixed with lime to form a lime slurry that is added to the crystallizer reactor. 
     
     
         14 . The process of  claim 6  where a polymer solution is added to the clarification step (g).