Process for obtaining treated coal and silica from coal containing fly ash

Abstract

A process for treating mixtures of solid coal and fly ash containing metallic oxides, silicon dioxide and sulfur compounds in order to produce treated coal and substantially pure silicon dioxide comprising (1) reacting a mixture of the coal and fly ash with hydrogen fluoride in water to produce a liquid stream comprising silicon fluoride and metal fluorides and a solids stream comprising unreacted coal and sulfur compounds; (2) reacting the sulfur compounds with metallic nitrates dissolved in water to form an aqueous solution of nitrate, metallic and sulfur ions; (3) separating the aqueous solution of nitrate, sulfur and metallic ions from the solid coal; (4) washing the previously treated solid coal with water; (5) reacting the silicon fluorides and metal fluorides with metallic nitrates in an aqueous mixture to form solid silicon dioxide; and separating the solid silicon dioxide from the aqueous mixture.

1 . A method for treating mixtures of solid coal and fly ash containing metallic oxides, silicon dioxide and sulfur compounds to produce reacted or treated coal and substantially pure silicon dioxide, comprising the steps of:
 reacting said mixture of coal and fly ash with hydrogen fluoride in water to produce a liquid stream comprising silicon fluoride and metal fluorides, and a solids stream comprising unreacted coal and sulfur compounds;   reacting said sulfur compounds with metallic nitrates dissolved in water to form an aqueous solution of nitrate, metallic and sulfur ions;   separating said aqueous solution of nitrate, sulfur and metallic ions from said solid coal;   washing said coal with water;   reacting said silicon fluoride and metal fluorides with metallic nitrates in an aqueous mixture to form solid silicon dioxide; and   separating said solid silicon dioxide from said aqueous mixture.   
     
     
         2 . A method according to  claim 1 , wherein said metallic oxides comprise Al 2 O 3  and Fe 2 O 3 . 
     
     
         3 . A method according to  claim 1 , wherein said sulfur compounds comprise iron and aluminum sulfides. 
     
     
         4 . A method according to  claim 1 , wherein the amount of fly ash remaining in said treated coal is less than about 0.01 wt. %. 
     
     
         5 . A method according to  claim 1 , wherein said reaction of silicon fluoride with metallic nitrates to form silicon dioxide occurs according to the following general formula:
   SiF 4 +2(Al 2 Fe)(NO 3 ) 3 +2H 2 O→SiO 2(s) +2(Al, Fe)F 2   + +4H + +6NO 3   −     
     
     
         6 . A method according to  claim 1 , wherein said reaction of silicon dioxide with hydrogen fluoride to produce silicon fluoride occurs according to the following general formula:
   SiO 2 +4HF→SiF 4 +2H 2 O   
     
     
         7 . A method according to  claim 3 , wherein iron sulfide reacts with iron nitrate according to the following general formula:
   FeS 2 +14Fe(NO 3)   3 +8H 2 O→2SO 4   2− +16H + +15Fe 2+ +42NO 3−     
     
     
         8 . A method according to  claim 1 , wherein said reaction of fly ash containing silicon dioxide occurs at a temperature of about 150° F. and at a pressure of about atmospheric. 
     
     
         9 . A method according to  claim 1 , further comprising the step of forming metallic nitrates for use in said reaction with sulfur compounds by reacting nitric acid (HNO 3 ) with metallic fluoride compounds having the general formula (Al,Fe)F 2 OH in water. 
     
     
         10 . A method according to  claim 1 , further comprising the step of recovering metallic oxides of aluminum and iron and regenerating hydrogen fluoride using a high temperature reaction according to the following general formula: 
       
         
           
           
               
               
           
         
       
     
     
         11 . A method according to  claim 10 , wherein said reaction occurs at a temperature of about 750° F.