Extraction of gold from cathode associated gold concentrates

Abstract

The invention involves a method for recovering gold from a gold concentrate comprising: dissolving gold from the concentrate in an aqueous liquor to provide a gold liquor; subjecting the gold liquor to electrolysis in an electrowinning cell to provide cathode-associated gold material; leaching the cathode associated gold material in an aqueous liquor under reducing conditions to provide a treated solid residue; and smelting the treated solid residue to recover gold.

1 . A method for recovering gold from a gold concentrate comprising:
 dissolving gold from the concentrate in an aqueous liquor to provide a gold liquor;   subjecting the gold liquor to electrolysis in an electrowinning cell to provide cathode-associated gold material;   leaching the cathode associated gold material in an aqueous liquor under reducing conditions to provide a treated solid residue; and   smelting the treated solid residue to recover gold.   
     
     
         2 . The method according to  claim 1  wherein the gold concentrate comprises carbon sorbed with gold and the method further comprises stripping gold from the carbon by contact with an aqueous liquor to provide said gold liquor. 
     
     
         3 . The method according to  claim 1  wherein the gold concentrate comprises a gravity concentrate and the method further comprises dissolving gold from the gravity concentrate to provide said gold liquor. 
     
     
         4 . The method according to  claim 1  wherein leaching the cathode associated gold material under reducing conditions involves use of an aqueous leach composition selected from the group consisting of aqueous base, aqueous acid, aqueous chelating agent, and mixtures of aqueous chelating agent with acid or base. 
     
     
         5 . The method according to  claim 1  wherein the aqueous reducing liquor is an acidic aqueous reducing liquor of pH less than about 1.5. 
     
     
         6 . The method according to  claim 1  wherein the aqueous reducing liquor is an alkaline aqueous reducing liquor. 
     
     
         7 . The method according to  claim 1  wherein the method further comprises leaching the deposited gold concentrate, prior to said reducing leach step, in an aqueous liquor comprising one or more agents selected from the group consisting of hydrochloric acid, nitric acid, alkali, lead acetate, chelating agents, carboxylic acids and their salts, chlorates, perchlorates, chlorides, fluorosilicate, phenol sulfonate, and peroxydisulfate. 
     
     
         8 . The method according to  claim 1  wherein the method further comprises subjecting the solid residue from leaching in aqueous reducing liquor to at least one leaching step in an aqueous liquor comprising agents selected from the group consisting of hydrochloric acid, nitric acid, alkali, lead acetate, chelating agents, carboxylic acids and their salts, chlorates, perchlorates, chlorides, fluorosilicate, phenol sulfonate, and peroxydisulfate. 
     
     
         9 . (canceled) 
     
     
         10 . The method of  claim 8  wherein the contact between at least one of the gold concentrate and residue and the aqueous liquor is carried out under conditions of ultrasonic agitation. 
     
     
         11 . The method for recovering gold according to  claim 10  wherein a mixture of the cathode-associated gold concentrate and reducing liquor is subject to ultrasonic radiation at a frequency in the range 10-60 kHz. 
     
     
         12 . The method for recovering gold according to  claim 1  wherein the cathode comprises steel wool and the method comprises treating the cathode having deposited gold material to remove the steel wool. 
     
     
         13 . The method of  claim 1  comprising a plurality of steps involving contact of the cathode associated gold material with an aqueous reducing liquor. 
     
     
         14 . The method according to  claim 1  wherein the reducing conditions are provided by a reducing agent. 
     
     
         15 . The method according to  claim 1  wherein the reducing conditions are provided by at least one reducing agent comprising metal species selected from the group consisting of chromium (Cr II), tin (Sn II), copper (Cu I) and titanium (Ti II, Ti III) and non-metal containing reducing agents selected from sulfites, organic acids with sulfites and oxalic acid. 
     
     
         16 . The method according to  claim 1  wherein the aqueous reducing liquor comprises stannous ion. 
     
     
         17 . The method according to  claim 1  comprising said reducing leach and a subsequent acid leach wherein the liquor used in the reducing leach comprises hydrochloric acid and stannous chloride and the liquor used in the subsequent acid leach comprises nitric acid in water. 
     
     
         18 . The method according to  claim 17  wherein the weight ratio of liquid to solid material in the subsequent acid leach step is in the range of 10:1 to 100:1. 
     
     
         19 . The method according to  claims 14  further comprising subjecting the solid residue from leaching in aqueous reducing liquor to leaching with an alkaline liquor. 
     
     
         20 . The method according to  claim 19  wherein the aqueous alkaline liquor has a pH greater than 13. 
     
     
         21 . The method for recovering gold according to  claim 19  wherein the alkaline liquor comprises at least 5% sodium hydroxide. 
     
     
         22 . The method according to  claim 1  wherein the reducing liquor comprises at least one agent selected from organic acids and their salts. 
     
     
         23 . The method according to  claim 1  wherein the reducing liquor comprises at least one base metal chelating agent selected from the group consisting of beta-diketones, amino polycarboxylic acids, salts of amino polycarboxylic acids, carboxylic acids, salts of carboxylic acids, and polyphosphonates. 
     
     
         24 . The method according to  claim 1  wherein the material subject to leaching in an aqueous reducing liquor is finely divided. 
     
     
         25 . The method according to  claim 1  wherein the material subject to leaching in aqueous liquor is finely divided providing on wet sieving at least 80% by weight passing through a 100 micron sieve. 
     
     
         26 . The method according to  claim 1  wherein the smelting of said residue in a crucible is conducted without addition of a flux. 
     
     
         27 . The method according to  claim 1  wherein the smelting of said residue is conducted in the presence of a borax flux. 
     
     
         28 . The method according to  claim 1  wherein the step of processing the residue to recover gold comprises forming a molten pool comprising at least one metal selected from copper, silver gold and platinum group metals. 
     
     
         29 . The method according to  claim 28  wherein the molten pool is formed from a solid particulate mixture comprising particles of treated solid residue and particles of at least one metal selected from copper, silver, gold and platinum group metals. 
     
     
         30 . The method according to  claim 28  wherein the molten pool is poured into a mold to form an ingot, bullion bar or dore bar. 
     
     
         31 . The method according to  claim 28  wherein the molten pool has a melting point in excess of 900° C. 
     
     
         32 . The method according to  claim 28  wherein the pool metal comprises silver, copper or mixtures thereof. 
     
     
         33 . The method according to  claim 28  wherein a particulate mixture of the residue and at least one metal selected from copper, silver gold and platinum group metals is gradually added to a heated crucible such that a molten pool is formed during addition and further particulate mixture is added to and becomes part of the molten pool. 
     
     
         34 . The method according to  claim 28  wherein a particulate mixture of the residue and at least one metal selected from copper, silver, gold and platinum group metals are gradually added to a preformed molten pool of borax. 
     
     
         35 . The method according to  claim 34  wherein the particulate mixture does not comprise particles of borax or other fluxing agents. 
     
     
         36 . The method according to  claim 28  wherein the melting step comprises adding the treated solid residue to a previously melted pool comprising at least one metal selected from copper, silver, gold and platinum group metals. 
     
     
         37 . The method according to  claim 28  wherein at least part of the treated solid residue is enclosed in a metal sheet or foil, preferably selected from at least one of copper, silver, gold and platinum group metals. 
     
     
         38 . The method according to  claim 27  wherein smelting is conducted in a crucible comprising a ceramic material, inert to molten borax. 
     
     
         39 . The method according to  claim 38  wherein smelting is conducted in a crucible which comprises less than 10% by weight carbon and less than 10% by weight of carbides. 
     
     
         40 - 43 . (canceled)