Method for removing impurities from coal in a reaction chamber

Abstract

A method for removing at least one impurity from coal is described herein. The method includes providing coal comprising a plurality of impurities and contacting the coal with an acid solution in a reaction chamber. At least one of the impurities reacts with the acid solution to produce one or more first products soluble in the acid solution. The method further includes removing at least a portion of the acid solution including at least a portion of the first products from the reaction chamber and adding a nitrate composition to the reaction chamber to form a nitrate solution. At least one of the impurities, at least one of the first products, or combinations thereof react with the nitrate composition to produce one or more second products soluble in the nitrate solution. The method still further includes removing at least a portion of the nitrate solution including at least a portion of the second products from the reaction chamber.

1 . A method for removing at least one impurity from coal, the method comprising:
 providing coal comprising a plurality of impurities;   contacting the coal with an acid solution in a reaction chamber, wherein at least one of the impurities reacts with the acid solution to produce one or more first products soluble in the acid solution;   removing at least a portion of the acid solution including at least a portion of the one or more first products from the reaction chamber;   adding a nitrate composition to the reaction chamber to form a nitrate solution, wherein at least one of the impurities, at least one of the first products, or combinations thereof react with the nitrate composition to produce one or more second products soluble in the nitrate solution; and   removing at least a portion of the nitrate solution including at least a portion of the one or more second products from the reaction chamber.   
     
     
         2 . The method of  claim 1 , wherein the acid solution comprises a hydrofluoric acid solution, a nitric acid solution, a hydrochloric acid solution, a hydrofluorosilicic acid solution, or combinations thereof. 
     
     
         3 . The method of  claim 1 , wherein the acid solution comprises a hydrofluoric acid solution having a hydrofluoric acid concentration of about 3 M to about 10 M. 
     
     
         4 . The method of  claim 1 , wherein the acid solution comprises a hydrofluoric acid solution, and wherein a weight ratio of hydrofluoric acid solution to coal in the step of contacting is about 10:1 to about 10:5. 
     
     
         5 . The method of  claim 1 , wherein the one or more first products comprises one or more fluorides, hydroxides, hydroxyfluorides, oxides, or combinations thereof. 
     
     
         6 . The method of  claim 5 , wherein the one or more first products comprises one or more fluorides selected from the group consisting of silicon fluoride, aluminum fluoride, iron fluoride, calcium fluoride, sodium fluoride, and combinations thereof. 
     
     
         7 . The method of  claim 1 , wherein the step of contacting comprises contacting the coal with the acid solution for about 1 hour to about 10 hours. 
     
     
         8 . The method of  claim 1 , wherein the step of contacting comprises contacting the coal with the acid solution at a temperature ranging from about 70° F. to about 200° F. 
     
     
         9 . The method of  claim 1 , wherein the nitrate composition comprises nitric acid, ferric nitrate, fluoronitrate, hydroxide, hydroxyl fluoride, hydroxynitrate, ions thereof, or combinations thereof. 
     
     
         10 . The method of  claim 1 , wherein the nitrate composition comprises a nitric acid solution having a nitric acid concentration of about 0.1 M to about 5 M. 
     
     
         11 . The method of  claim 1 , wherein the nitrate composition comprises a nitric acid solution, and wherein the weight ratio of nitric acid solution to coal in the step of adding is about 10:1 to about 10:5. 
     
     
         12 . The method of  claim 1 , wherein the one or more second products comprises nitrate ions, sulfate ions, iron ions, hydroxyfluorides, oxides, fluoro nitrates, or combinations thereof. 
     
     
         13 . The method of  claim 1 , further comprising, before the step of removing the nitrate solution, maintaining the nitrate solution in the reaction chamber for about 20 hours to about 30 hours. 
     
     
         14 . The method of  claim 1 , further comprising, before the step of removing the nitrate solution, maintaining the nitrate solution in the reaction chamber at a temperature ranging from about 70° F. to about 190° F. 
     
     
         15 . The method of claim of  1 , wherein the plurality of impurities comprise oxides of aluminum, iron, potassium, calcium, sodium, minerals, inorganic and organic sulfur compounds, alkalis, ash, or combinations thereof. 
     
     
         16 . The method of  claim 1 , wherein, after the step of removing the nitrate solution, ash is present in the coal in an amount less than about 0.1% by weight. 
     
     
         17 . The method of  claim 1 , wherein, after the step of removing the nitrate solution, ash is present in the coal in an amount of about 0.1% by weight to about 1% by weight. 
     
     
         18 . The method of  claim 1 , further comprising agitating the acid solution in the reaction chamber, agitating the nitrate solution in the reaction chamber, or both. 
     
     
         19 . The method of  claim 1 , further comprising, after the step of removing the nitrate solution, water washing the coal. 
     
     
         20 . The method of  claim 1 , wherein the coal is provided in batches of about 300 tons to about 10,000 tons in the reaction chamber.