Processes for treating fly ashes

Abstract

There are provided processes for treating fly ash. For example, the processes can comprise leaching fly ash with HCl so as to obtain a leachate comprising aluminum ions and a solid, and separating the solid from the leachate; reacting the leachate with HCl so as to obtain a liquid and a precipitate comprising the aluminum ions in the form of AlCl 3 , and separating the precipitate from the liquid; and heating the precipitate under conditions effective for converting AlCl 3 into Al 2 O 3 and optionally recovering gaseous HCl so-produced.

What is claimed is: 
     
         1 . A process for treating raw fly ash, said process comprising:
 optionally a pre-leaching treatment that consists of reducing the particle size of said raw fly ash;   leaching said raw fly ash with HCl under conditions effective to obtain a leachate comprising aluminum ions and iron ions and a solid, and separating said solid from said leachate;   reacting said leachate with HCl so as to increase concentration of HCl in said leachate under conditions effective to decrease solubility of AlCl 3  and to substantially selectively precipitate aluminum ions, thereby obtaining a liquid comprising iron ions and a precipitate comprising said aluminum ions in the form of AlCl 3 , and separating said precipitate from said liquid; and   heating said precipitate under conditions effective for converting AlCl 3  into Al 2 O 3  and optionally recovering gaseous HCl so-produced.   
     
     
         2 . The process of  claim 1 , wherein said fly ash is leached with HCl having a concentration of about 25 to about 45 weight %. 
     
     
         3 . The process of  claim 1 , wherein said fly ash is leached with HCl having a concentration of about 25 to about 45 weight % at a temperature of about 125 to about 225° C. 
     
     
         4 . The process of  claim 1 , wherein said fly ash is leached with HCl having a concentration of about 25 to about 45 weight % at a temperature of about 160 to about 190° C. 
     
     
         5 . The process of  claim 1 , wherein said liquid comprises at least one iron chloride. 
     
     
         6 . The process of  claim 5 , wherein said at least one iron chloride is FeCl 3 . 
     
     
         7 . The process of  claim 6 , wherein said liquid is concentrated to a concentrated liquid having a concentration of said at least one iron chloride of at least 30% by weight; and then hydrolyzed at a temperature of about 155 to about 350° C. 
     
     
         8 . The process of  claim 1 , wherein said process comprises reacting said leachate with gaseous HCl so as to obtain said liquid and said precipitate comprising said aluminum ions, said precipitate being formed by crystallization of AlCl 3 .6H 2 O. 
     
     
         9 . The process of  claim 1 , wherein said process comprises reacting said leachate with dry gaseous HCl so as to obtain said liquid and said precipitate comprising said aluminum ions, said precipitate being formed by crystallization of AlCl 3 .6H 2 O. 
     
     
         10 . The process of  claim 1 , wherein said process comprises reacting said leachate with HCl recovered during said process and having a concentration of at least 30% as to obtain said liquid and said precipitate comprising said aluminum ions, said precipitate being formed by crystallization of AlCl 3 .6H 2 O. 
     
     
         11 . The process of  claim 1 , wherein said process comprises saturating said leachate with gaseous HCl having a concentration of at least 85% by weight so as to obtain said liquid and said precipitate comprising said aluminum ions, said precipitate being formed by crystallization of AlCl 3 .6H 2 O. 
     
     
         12 . The process of  claim 1 , wherein said process comprises saturating said leachate with dry gaseous HCl so as to obtain said liquid and said precipitate comprising said aluminum ions, said precipitate being formed by crystallization of AlCl 3 .6H 2 O. 
     
     
         13 . The process of  claim 1 , wherein said process comprises reacting said leachate with HCl in a reactor so as to increase concentration of free HCl in said reactor and to obtain said liquid and said precipitate comprising said aluminum ions, said precipitate being formed by crystallization of AlCl 3 .6H 2 O. 
     
     
         14 . The process of  claim 13 , wherein said process comprises increasing concentration of free HCl in said reactor with gaseous HCl. 
     
     
         15 . The process of  claim 14 , wherein said gaseous HCl has a HCl concentration of at least 85% by weight. 
     
     
         16 . The process of  claim 1 , wherein said process comprises converting AlCl 3 .6H 2 O into Al 2 O 3  by carrying out a calcination of AlCl 3 .6H 2 O. 
     
     
         17 . The process of  claim 1 , wherein said process comprises converting AlCl 3 .6H 2 O into Al 2 O 3  by carrying out a calcination of AlCl 3 .6H 2 O, said calcination comprising steam injection. 
     
     
         18 . A process for treating fly ash, said process comprising:
 carrying out a pre-leaching removal of fluorine optionally contained in said fly ash;   leaching fly ash with HCl so as to obtain a leachate comprising aluminum ions and iron ions and a solid, and separating said solid from said leachate;   reacting said leachate with HCl so as to obtain a liquid comprising said iron ions and a precipitate comprising said aluminum ions in the form of AlCl 3 , and separating said precipitate from said liquid; and   heating said precipitate under conditions effective for converting AlCl 3  into Al 2 O 3  and optionally recovering gaseous HCl so-produced.   
     
     
         19 . A process for treating fly ash, the process comprising:
 leaching said fly ash comprising a first metal with HCl so as to obtain a leachate comprising ions of said first metal and a solid, and separating the solid from the leachate;   reacting the leachate with HCl so as to obtain a liquid and a precipitate comprising a chloride of the first metal, and separating the precipitate from the liquid; and   heating the precipitate under conditions effective for converting the chloride of the first metal into an oxide of the first metal.   
     
     
         20 . A process for treating fly ash comprising:
 leaching fly ash with an acid so as to obtain a leachate and a solid residue, and separating said leachate from said solid residue;   at least partially removing iron ions from said leachate by substantially selectively precipitating said iron ions at a pH greater than 10 by reacting said leachate with a base and at least partially removing said precipitated iron ions from said leachate, thereby obtaining an Al-rich composition comprising Al 3+  ions;   optionally purifying said Al 3+  ions; and   converting said Al 3+  ions into alumina.