Method for processing precious metal source materials

Abstract

A method is disclosed for recovering precious metals from source materials containing precious metals which involves leaching the source material in aqueous reducing liquor to provide a treated solid residue and processing the treated residue to recover precious metals.

1 . A method for recovering precious metals from source materials containing precious metals the method comprising leaching the source material in aqueous reducing liquor to provide a treated solid residue and processing the treated residue to recover precious metals. 
     
     
         2 . A method according to  claim 1  wherein the source materials is selected from the group consisting of carbon sorbed precious metals, concentrates derived by ashing of precious metal containing material, electrode-associated material from an electrolytic process and gravity gold. 
     
     
         3 . A method according to  claim 1  wherein the processing of the treated residue comprises one or more of smelting the residue, selectively solubilising one or more precious metals and electrorefining. 
     
     
         4 . A method according to  claim 1  wherein the source material is in particulate form. 
     
     
         5 . A method according to  claim 4  wherein the source material on wet sieving provides at least 80% by weight passing through a 100 micron sieve. 
     
     
         6 . A method according to  claim 1  wherein the source material is an electrode associated material selected from (a) cathode associated precious metals produced in electrowinning of gold from aqueous liquors used to dissolve gold; and (b) anode mud produced in refining of base metals. 
     
     
         7 . A method according to  claim 1  wherein the method further comprises isolating the reduced solid residue and treating the residue by leaching in an aqueous liquor comprising at least one agent selected from the group consisting of hydrochloric acid, nitric acid, alkali, lead acetate, ammonium chloride, calcium chloride, strontium chloride, acetic acid, and chelating agents. 
     
     
         8 . A method according to  claim 1  wherein the solid residue is leached with an aqueous alkaline liquor and the solid residue from the alkaline liquor is further refined to provide precious metal. 
     
     
         9 . A method according to  claim 1  wherein the aqueous reducing liquor is provided by a reducing agent. 
     
     
         10 . A method according to  claim 1  wherein the aqueous reducing liquor comprises a reducing agent selected from the group consisting of (A) metal-containing reducing agents selected from the group consisting of chromium (Cr II), tin (Sn II), copper (Cu I) and titanium (Ti II, Ti III), and (B) non-metal containing reducing agents selected from the group consisting of sulfites, oxalic acid, formic acid, hydrazine, acetates including acetic acid, citrates including citric acid, sulfite, and dithionite. 
     
     
         11 . A method according to  claim 1  wherein the reducing leach produces at least partial removal of base metal from the source material. 
     
     
         12 . A method according to  claim 1  wherein the reducing liquor in at least one contact between with source material has a pH of less than about 1.5. 
     
     
         13 . A method according to  claim 1  further comprising leaching the precious metal 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, chelating agents, carboxylic acids and their salts, chlorates, perchlorates, chlorides, fluorosilicates, phenol sulfate and peroxydisulfate. 
     
     
         14 . (canceled) 
     
     
         15 . A method according to  claim 13  wherein the further leaching step uses a carboxylic acid selected from the group consisting of formic acid, acetic acid, lactic acid, citric acid, isobutyric acid and salts thereof. 
     
     
         16 . A method according to  claim 13  wherein further leaching step uses a chloride selected from the group consisting of ammonium chloride, sodium chloride, potassium chloride, calcium chloride and strontium chloride. 
     
     
         17 . A method according to  claim 1  wherein the leaching of the source material in aqueous reducing liquor conditions is conducted with ultrasonic agitation at a frequency in the range 10-60 kHz. 
     
     
         18 . (canceled) 
     
     
         19 . A method according to  claim 1  wherein the leaching of the source material in aqueous reducing liquor is conducted at a temperature above at least 60° C. 
     
     
         20 . A method according to  claim 1  wherein the precious source material is cathodic material or cathodic sludge from a electro-winning of a strip liquor. 
     
     
         21 . A method according to  claim 1  wherein the precious metal concentrate source material comprises gold sorbed onto carbon. 
     
     
         22 . A method according to  claim 1  wherein the source material comprises anode mud from a base metal refining process. 
     
     
         23 . A method according to  claim 1  wherein the treated residue is processed to recover precious metals by a method further comprising forming a molten pool comprising at least one metal selected from the group consisting of copper, silver, gold and platinum group metals; and adding at least part of the treated residue into the pool of molten metal. 
     
     
         24 . A method according to  claim 23  wherein the refining step comprises adding said residue or product of further treatment to a crucible, and heating the contents to smelting temperature. 
     
     
         25 . A method according to  claim 24  wherein a flux is added to contents of the crucible. 
     
     
         26 . A method according to  claim 23  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. 
     
     
         27 . A method according to  claim 26  wherein the particulate mixture of the residue and at least one metal selected from copper, silver and gold 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. 
     
     
         28 . A method according to  claim 26  wherein the 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. 
     
     
         29 - 31 . (canceled) 
     
     
         32 . A method according to  claim 23  wherein smelting is conducted in a crucible comprising a ceramic material. 
     
     
         33 . A method according to  claim 23  wherein smelting is conducted in a crucible which comprises less than 10% by weight carbon and less than 10% by weight carbides. 
     
     
         34 - 36 . (canceled)