Stripping agent and method of use

Abstract

A method of removing mercury adsorbed onto activated carbon is provided. The method includes treating an adsorbed mixture of metal cyanide complexes on a carbon substrate with an acidic solution of a stripping agent that is a weak acid. The method also eliminates inorganic scalants from the carbon substrate. In precious metal mining operations, the disclosed method reduces environmental emissions of mercury during the gold elution and carbon reactivation processes.

What is claimed is: 
     
         1 . A method of removing mercury from an adsorbed mixture comprising mercury and gold that is adsorbed on a carbon substrate, the method comprising:
 desorbing mercury from the carbon substrate by contacting the adsorbed mixture with an acidic aqueous solution comprising a stripping agent that is a weak acid.   
     
     
         2 . The method of  claim 1 , wherein prior to desorbing mercury from the carbon substrate, the method further comprises:
 adsorbing mercury and gold on the carbon substrate to form the adsorbed mixture, which includes mercury and gold.   
     
     
         3 . The method of  claim 1 , wherein the weak acid comprises phosphoric acid. 
     
     
         4 . The method of  claim 1 , wherein the weak acid comprises an organic acid. 
     
     
         5 . The method of  claim 1 , wherein the weak acid comprises a carboxylic acid. 
     
     
         6 . The method of  claim 5 , wherein the carboxylic acid is a mono acid. 
     
     
         7 . The method of  claim 6 , wherein the mono acid is selected from the group consisting of formic acid, acetic acid, and propionic acid. 
     
     
         8 . The method of  claim 1 , wherein the acidic solution further comprises an alcohol. 
     
     
         9 . The method of  claim 1 , wherein desorbing mercury from the carbon substrate comprises contacting the adsorbed mixture with the acidic aqueous solution at a temperature from about 40° C. to about 120° C. 
     
     
         10 . The method of  claim 1 , wherein desorbing mercury from the carbon substrate comprises contacting the adsorbed mixture with the acidic aqueous solution at a temperature from about 60° C. to about 100° C. 
     
     
         11 . The method of  claim 1 , wherein desorbing mercury from the carbon substrate comprises contacting the adsorbed mixture with the acidic aqueous solution at a temperature from about 80° C. to about 90° C. 
     
     
         12 . The method of  claim 1 , wherein the weak acid is present in a concentration greater than 0% and less than about 30% by volume of the acidic aqueous solution. 
     
     
         13 . The method of  claim 1 , wherein the weak acid is present in a concentration from about 5% to about 20% by volume of the acidic aqueous solution. 
     
     
         14 . The method of  claim 1 , wherein the weak acid is present in a concentration from about 5% to about 10% by volume of the acidic aqueous solution. 
     
     
         15 . A method of removing an inorganic scalant from an adsorbed mixture comprising the inorganic scalant, mercury, and gold that is adsorbed on an activated carbon used in a precious metal recovery processes, the method comprising:
 desorbing the inorganic scalant from the carbon substrate by contacting the adsorbed mixture with an acidic aqueous solution comprising a stripping agent that is a weak acid.   
     
     
         16 . The method of  claim 15 , wherein the weak acid comprises phosphoric acid. 
     
     
         17 . The method of  claim 15 , wherein the weak acid comprises an organic acid. 
     
     
         18 . The method of  claim 15 , wherein the weak acid comprises a carboxylic acid. 
     
     
         19 . The method of  claim 18 , wherein the carboxylic acid is a mono acid. 
     
     
         20 . The method of  claim 19 , wherein the mono acid is selected from the group consisting of formic acid, acetic acid, and propionic acid. 
     
     
         21 . The method of  claim 15 , wherein the acidic solution further comprises an alcohol. 
     
     
         22 . The method of  claim 15 , wherein desorbing the inorganic scalant from the carbon substrate comprises contacting the adsorbed mixture with the acidic aqueous solution at a temperature from about 40° C. to about 120° C. 
     
     
         23 . The method of  claim 15 , wherein desorbing the inorganic sealant from the carbon substrate comprises contacting the adsorbed mixture with the acidic aqueous solution at a temperature from about 60° C. to about 100° C. 
     
     
         24 . The method of  claim 15 , wherein desorbing the inorganic sealant from the carbon substrate comprises contacting the adsorbed mixture with the acidic aqueous solution at a temperature from about 80° C. to about 90° C. 
     
     
         25 . The method of  claim 15 , wherein the weak acid is present in a concentration greater than 0% and less than about 30% by volume of the acidic aqueous solution. 
     
     
         26 . The method of  claim 15 , wherein the weak acid is present in a concentration from about 5% to about 20% by volume of the acidic aqueous solution. 
     
     
         27 . The method of  claim 15 , wherein the weak acid is present in a concentration from about 5% to about 10% by volume of the acidic aqueous solution. 
     
     
         28 . The method of  claim 15 , wherein the inorganic sealant includes a calcium precipitate. 
     
     
         29 . The method of  claim 28 , wherein the calcium precipitate is calcium carbonate. 
     
     
         30 . The method of  claim 28 , wherein the calcium precipitate is calcium sulfate. 
     
     
         31 . The method of  claim 15 , wherein desorbing the inorganic sealant from the carbon substrate by contacting the adsorbed mixture with the acidic aqueous solution further includes desorbing mercury from the carbon substrate. 
     
     
         32 . A method of reducing mercury emissions in precious metal mining operations, comprising:
 washing an adsorbed mixture comprising mercury and gold that is adsorbed on an activated carbon substrate with an acidic aqueous solution comprising a stripping agent that is a weak acid, wherein at least a portion of a first amount of mercury is desorbed from the activated carbon substrate;   removing at least a portion of the gold from the activated carbon substrate; and   regenerating the activated carbon substrate by heating, wherein a second amount of mercury remaining on the activated carbon substrate is volatilized from the activated carbon substrate, the second amount of mercury is less than the first amount of mercury.   
     
     
         33 . The method of  claim 32 , wherein the weak acid comprises phosphoric acid. 
     
     
         34 . The method of  claim 32 , wherein the weak acid comprises an organic acid. 
     
     
         35 . The method of  claim 32 , wherein the weak acid comprises a carboxylic acid. 
     
     
         36 . The method of  claim 35 , wherein the carboxylic acid is a mono acid. 
     
     
         37 . The method of  claim 36 , wherein the mono acid is selected from the group consisting of formic acid, acetic acid, and propionic acid. 
     
     
         38 . The method of  claim 32 , wherein the acidic aqueous solution further comprises an alcohol. 
     
     
         39 . The method of  claim 32 , wherein the mercury is desorbed from the carbon substrate by washing the adsorbed mixture with the acidic aqueous solution at a temperature from about 40° C. to about 120° C. 
     
     
         40 . The method of  claim 32 , wherein the mercury is desorbed from the carbon substrate by washing the adsorbed mixture with the acidic aqueous solution at a temperature from about 60° C. to about 100° C. 
     
     
         41 . The method of  claim 32 , wherein the mercury is desorbed from the carbon substrate by washing the adsorbed mixture with the acidic aqueous solution at a temperature from about 80° C. to about 90° C. 
     
     
         42 . The method of  claim 32 , wherein the weak acid is present in a concentration greater than 0% and less than about 30% by volume of the acidic aqueous solution. 
     
     
         43 . The method of  claim 32 , wherein the weak acid is present in a concentration from about 5% to about 20% by volume of the acidic aqueous solution. 
     
     
         44 . The method of  claim 32 , wherein the weak acid is present in a concentration from about 5% to about 10% by volume of the acidic aqueous solution.