Producing Calcium Cyanide At A Mine Site Using Easily Transportable Starting Materials

Abstract

The present invention is a method by which the mine can obtain a supply of calcium cyanide for use in its leaching operations. Specifically, one preferred method within the scope of the invention involves producing hydrogen cyanide directly at a mine site using formamide as a starting material. Alternative methods of producing hydrogen cyanide at the mine site using easily transportable starting materials, such as methanol and urea, are disclosed. The hydrogen cyanide is neutralized at the mine site with slaked lime (Ca(OH) 2 ) to form the calcium cyanide.

1 . A method for producing an aqueous solution of calcium cyanide directly at a mine site, the method comprising:
 obtaining a supply of formamide at the mine site;   reacting the formamide at the mine site to produce a quantity of hydrogen cyanide; and   contacting the quantity of hydrogen cyanide at the mine site with slaked lime to produce a supply of calcium cyanide.   
   
   
       2 . The method according to  claim 1  wherein the slaked lime comprises primarily calcium hydroxide. 
   
   
       3 . The method according to  claim 1  further comprising the step of diluting the calcium cyanide to concentrations that may be used in at the mine site in at least one mining operation. 
   
   
       4 . A method for producing an aqueous solution of calcium cyanide directly at a mine site, the method comprising:
 obtaining a supply of ammonia at the mine site;   obtaining a supply of methanol at the mine site;   reacting the ammonia and methanol at the mine site to produce a quantity of hydrogen cyanide; and   contacting the quantity of hydrogen cyanide at the mine site with slaked lime to produce a supply of calcium cyanide.   
   
   
       5 . The method according to  claim 4  wherein the ammonia is obtained by decomposing urea. 
   
   
       6 . The method according to  claim 4  wherein the slaked lime comprises primarily calcium hydroxide. 
   
   
       7 . The method according to  claim 4  further comprising the step of diluting the calcium cyanide to concentrations that may be used in at the mine site in at least one mining operation. 
   
   
       8 . A method of mining precious metals using a calcium cyanide solution comprising:
 producing the calcium cyanide solution at a mine site from at least one starting material;   leaching an area of interest at the mine site with the cyanide solution;   collecting a pregnant solution which contains a quantity of precious metal ions bound to cyanide anions as an aqueous complex; and   recovering the precious metal ions from the pregnant solution.   
   
   
       9 . The method of mining according to  claim 8  wherein the producing step comprises decomposing formamide to form hydrogen cyanide and neutralizing the hydrogen cyanide with slaked lime to form the calcium cyanide solution. 
   
   
       10 . The method of mining according to  claim 8  wherein the producing step comprises creating the cyanide solution using methanol and urea as the starting materials. 
   
   
       11 . The method of mining according to  claim 8  wherein producing step comprises producing a quantity of hydrogen cyanide that is then converted into a solution of calcium cyanide using lime or slaked lime. 
   
   
       12 . A method for producing calcium cyanide directly at a mine site, the method comprising:
 obtaining a supply of the starting materials at the mine site for use in an Andrussow process for producing hydrogen cyanide;   reacting the starting materials at the mine site to produce a quantity of hydrogen cyanide; and   processing the quantity of hydrogen cyanide at the mine site to produce a supply of calcium cyanide.   
   
   
       13 . The method according to  claim 12  wherein the processing step is accomplished by contacting the hydrogen cyanide with slaked lime to produce the calcium cyanide.