Method for oxidizing carbonaceous ores to facilitate precious metal recovery

Abstract

A method of oxidizing carbonaceous ores to assist in the recovery of metals is provided. The method includes the steps of heating a bed of carbonaceous ore in the reaction chamber of a reactor vessel, using microwave energy to initiate and sustain oxidation of the carbonaceous ore within the bed into carbon dioxide, controlling the inflow of oxygen into the reaction chamber to provide sufficient oxygen to maintain the reaction C+O 2 ═CO 2 , and monitoring the depletion of carbon from the carbonaceous ore.

1 . A method of recovering precious metals from a carbonaceous precious metal-containing material, comprising: 
 (a) passing microwave energy through the carbonaceous precious metal-containing material in a reaction chamber of a reactor vessel;    (b) during step (a), passing a molecular oxygen-containing gas through reaction chamber to oxidize carbon in the precious metal-containing material and form an oxidized precious metal-containing material; and    (c) when at least most of the carbon in the precious metal-containing material is converted into gaseous carbon oxides, removing the oxidized precious metal-containing material from the reaction chamber.    
     
     
         2 . The method of  claim 1 , wherein the carbon-containing components of the carbonaceous precious metal-containing material is heated to a temperature ranging from about 450 to about 750° C.  
     
     
         3 . The method of  claim 2 , wherein a microwave energy source comprising one or more individual generating units generating the microwave energy has a power level in the range of about 1 kw to about 150 kw per generating unit, operates at a frequency ranging from about 300 MHz to about 20 GHz, wherein the reaction chamber has a Q value ranging from about 1,000 to about 25,000, and wherein the microwave energy delivered to the carbonaceous precious metal-containing material ranges from about 250 to about 300,000 Joules/gm.  
     
     
         4 . The method of  claim 2 , wherein the temperature ranges from about 480 to about 650° C.  
     
     
         5 . The method of  claim 1 , further comprising: 
 (d) cyanide leaching the precious metal from the oxidized precious metal-containing material.    
     
     
         6 . The method of  claim 1 , wherein step (c) comprises the substeps: 
 (C1) determining when a temperature of the oxidized precious metal-containing material decreases by at least about 100° C. notwithstanding the continued application of microwave energy to the oxidized precious metal-containing material; and    (C2) in response to substep (C1), determining that at least most of the carbon in the precious metal-containing material is converted into gaseous carbon oxides.    
     
     
         7 . A precious metal recovered by the process of  claim 1 .  
     
     
         8 . A method of recovering gold, comprising: 
 (a) passing microwave energy through a bed of a carbonaceous precious metal-containing material, the bed being in a reactor vessel;    (b) passing a molecular oxygen-containing gas through the bed during step (a) to oxidize at least most of the carbon in the material and form gaseous carbon oxides;    (c) when at least most of the carbon in the material is removed from the oxidized precious metal-containing material, removing the oxidized precious metal-containing material from the reactor vessel; and    (d) recovering, by cyanidation leaching, at least most of the precious metal in the oxidized precious metal-containing material.    
     
     
         9 . The method of  claim 8 , further comprising: 
 (e) grinding the oxidized precious metal-containing material after step (c) and before step (d).    
     
     
         10 . The method of  claim 8 , wherein the carbon-containing components of the carbonaceous precious metal-containing material is heated to a temperature ranging from about 450 to about 1,000° C., wherein a microwave energy source comprising one or more individual generating units generating the microwave energy has a power level in the range of about 1 kw to about 150 kw per generating unit, operates at a frequency ranging from about 300 MHz to about 20 GHz, wherein the reaction chamber has a Q value ranging from about 1,000 to about 25,000, and wherein the microwave energy delivered to the carbonaceous precious metal-containing material ranges from about 250 to about 300,000 Joules/gm.  
     
     
         11 . The method of  claim 8 , wherein step (c) comprises the substeps: 
 (C1) determining when a temperature of the oxidized precious metal-containing material decreases by at least about 50° C. notwithstanding the continued application of microwave energy to the oxidized precious metal-containing material; and    (C2) in response to substep (C1), determining that at least most of the carbon in the precious metal-containing material is converted into gaseous carbon oxides.    
     
     
         12 . The method of  claim 8 , wherein the reactor vessel is selected from the group consisting of a fluidized bed reactor, a rotary kiln, and a plug flow reactor.  
     
     
         13 . A precious metal recovered by the method of  claim 8 .  
     
     
         14 . A method, comprising: 
 (a) providing a carbon-containing and gold-containing material;    (b) locating the material in a reactor chamber;    (c) passing microwave energy through the material while positioned in the reactor chamber;    (d) during step (c), passing a molecular oxygen-containing gas through the material to oxidize the carbon into gaseous carbon oxides and form an oxidized gold-containing material;    (e) monitoring the removal of carbon from the material;    (f) when at least most of the carbon has been removed from the material, removing the oxidized material from the reactor chamber;    (g) contacting the oxidized material with a cyanide lixiviant to form a pregnant leach solution comprising at least most of the gold in the oxidized material; and    (h) recovering the gold from the pregnant leach solution.    
     
     
         15 . The method of  claim 14 , wherein the carbon-containing components of the carbonaceous precious metal-containing material are heated to a temperature ranging from about 450 to about 1,000° C., wherein a microwave energy source comprising one or more individual generating units generating the microwave energy has a power level in the range of about 1 kw to about 150 kw per unit, operates at a frequency ranging from about 300 MHz to about 20 GHz, wherein the reaction chamber has a Q value ranging from about 1,000 to about 25,000, and wherein the microwave energy delivered to the carbon-containing and gold-containing material ranges from about 250 to about 300,000 Joules/gm.  
     
     
         16 . The method of  claim 14 , wherein step (e) comprises the substeps: 
 (E1) determining when a temperature of the oxidized gold-containing material decreases by at least about 50° C. notwithstanding the continued application of microwave energy to the oxidized gold-containing material; and    (E2) in response to substep (E1), determining that at least most of the carbon in the gold-containing material is converted into gaseous carbon oxides.    
     
     
         17 . The method of  claim 14 , wherein the reactor vessel is selected from the group consisting of a fluidized bed reactor, a rotary kiln, and a plug flow reactor.  
     
     
         18 . Gold recovered by the method of  claim 14.