Methods, Materials and Techniques for Precious Metal Recovery

Abstract

Materials and methods for precious metal recovery are disclosed. Usable leaching solutions are preferably aqueous based and include appropriate materials in sufficient quantities to solubilize and stabilize precious metal. Such materials typically include phosphoric acid and an oxidant material. Some or all of the oxidant material can be, in some instances, generated in-situ. The leaching solution is typically contacted with a substrate having a target precious metal, thereby solubilizing precious metal to form a stable, pregnant solution. The precious metal can then be recovered from the pregnant solution. In some instances, components of the leaching solution can be regenerated and reused in subsequent leaching.

What is claimed is: 
     
         1 . A method for recovering a precious metal from a precious metal-containing substrate, the method comprising:
 (i) combining the precious metal-containing substrate with an aqueous-based leaching solution to form solids and a pregnant leach solution, wherein the aqueous-based leaching solution comprises:
 an iodide salt material; 
 an iodate salt material, a chlorite salt material, or any combination thereof; and 
 phosphoric acid; and 
   (ii) separating the solids from the pregnant leach solution.   
     
     
         2 . The method according to  claim 1 , wherein:
 the precious metal-containing substrate comprises ore, mining tails, electronic waste, or any combination thereof; and   the precious metal and the pregnant leach solution comprise gold.   
     
     
         3 . The method according to  claim 1 , wherein the method further comprises, prior to step (i), passing the aqueous-based leaching solution through an electrochemical cell to reach an oxidation reduction potential (ORP) of at least 540 mV. 
     
     
         4 . The method according to  claim 1 , wherein the method further comprises, prior to step (i), passing the aqueous-based leaching solution through an electrochemical cell to reach an oxidation reduction potential (ORP) in a range from 540 mV to 650 mV. 
     
     
         5 . The method according to  claim 4 , wherein the electrochemical cell comprises conductive diamond electrodes. 
     
     
         6 . The method according to  claim 1 , wherein the method further comprises:
 (iii) removing the precious metal from the pregnant leach solution, thereby forming a barren leaching solution; and   (iv) increasing the oxidation reduction potential (ORP) of the barren leaching solution to at least 540 mV to form a regenerated aqueous-based leaching solution.   
     
     
         7 . The method according to  claim 1 , wherein the pregnant leach solution contains:
 less than 350 mg/L of copper; and   less than 3 mg/L of iron.   
     
     
         8 . The method according to  claim 1 , wherein the pregnant leach solution contains an amount of copper that is at least 75% less than a pregnant leaching solution produced by an otherwise identical process conducted with an aqueous leaching solution containing a carboxylic acid instead of phosphoric acid. 
     
     
         9 . The method according to  claim 1 , wherein the pregnant leach solution contains an amount of iron that is at least 75% less than a pregnant leaching solution produced by an otherwise identical process conducted with an aqueous leaching solution containing a carboxylic acid instead of phosphoric acid. 
     
     
         10 . The method according to  claim 1 , wherein:
 the iodide salt material comprises sodium iodide and/or potassium iodide;   the iodate salt material comprises sodium iodate and/or potassium iodate; and   the chlorite salt material comprises sodium chlorite and/or potassium chlorite.   
     
     
         11 . The method according to  claim 1 , wherein the aqueous-based leaching solution contains:
 from 5 to 90 grams per liter of the iodide salt material;   from 1 to 20 grams per liter of the iodate salt material and/or the chlorite salt material; and   from 1 to 40 grams per liter of the phosphoric acid.   
     
     
         12 . The method according to  claim 1 , wherein the aqueous-based leaching solution is characterized by an oxidation reduction potential (ORP) in a range from 540 mV to 650 mV. 
     
     
         13 . An aqueous-based leaching solution for a precious metal, the aqueous-based leaching solution comprising:
 an iodide salt material;   an iodate salt material, a chlorite salt material, or any combination thereof; and   phosphoric acid.   
     
     
         14 . The aqueous-based leaching solution according to  claim 13 , wherein the iodide salt material is present in the solution at a concentration of at least 5 grams per liter but no greater than 90 grams per liter. 
     
     
         15 . The aqueous-based leaching solution according to  claim 13 , wherein the phosphoric acid is present in the solution at a concentration of at least 1 gram per liter but no greater than 40 grams per liter. 
     
     
         16 . The aqueous-based leaching solution according to  claim 13 , wherein the phosphoric acid is present in the solution at a concentration of at least 5 grams per liter but no greater than 20 grams per liter. 
     
     
         17 . The aqueous-based leaching solution according to  claim 13 , wherein:
 the iodide salt material comprises sodium iodide and/or potassium iodide;   the iodate salt material comprises sodium iodate and/or potassium iodate; and   the chlorite salt material comprises sodium chlorite and/or potassium chlorite.   
     
     
         18 . The aqueous-based leaching solution according to  claim 13 , wherein the solution is characterized by an oxidation reduction potential (ORP) in a range from 540 mV to 650 mV. 
     
     
         19 . The aqueous-based leaching solution according to  claim 13 , wherein the solution further comprises potassium bromide, sodium bromide, potassium chloride, sodium chloride, or any combination thereof. 
     
     
         20 . The aqueous-based leaching solution according to  claim 13 , wherein the solution is prepared by a process comprising:
 combining the iodide salt material, the phosphoric acid, the chlorite salt material and/or the iodate salt material, and water in an agitated tank.