Enhanced recovery of gold

Abstract

An improved method for recovering refractory gold from a material comprising treating the material to at least partially remove nitric acid-insoluble lead moieties.

1 . An improved method for recovering refractory gold from a material comprising treating the material to at least partially remove nitric acid-insoluble lead moieties. 
     
     
         2 . A method according to  claim 1  comprising treating the material to transform at least a portion of the nitric acid insoluble lead moieties into leachable lead moieties and leaching the material to remove the leachable lead moieties. 
     
     
         3 . A method according to  claim 1  wherein the process of at least partially removing nitric acid-insoluble lead moieties from the gold containing material comprises contacting the gold containing material with an agent selected from the group consisting of reducing agents, lead complexing agents and lead solubilising agents. 
     
     
         4 . A method according to  claim 1  comprising contacting the material with a reducing agent. 
     
     
         5 . A method according to  claim 4  wherein the reducing agent is selected from the group consisting of chromium(II), tin(II), copper(I), titanium(II) and titanium(III) moieties, and also comprises sulfites, sulphur-containing reducing agents, oxalic acid, and other organic reducing agents. 
     
     
         6 . A method according to  claim 1  comprising contacting the gold containing material with a lead complexing agent. 
     
     
         7 . A method according to  claim 6  wherein the lead solubilising and complexing agents are selected from the group consisting of carboxylic acids and their salts, chlorates, perchlorates, alkalis, chlorides, fluorosilicate, phenol sulfonate and peroxy-disulfonate. 
     
     
         8 . A method according to  claim 7  wherein (a) the carboxylic acids are selected from the group consisting of citric acid, lactic acid, acetic acid, formic acid, iso-butyric acid, acetyl salicylic acid and their salts and (b) the chlorides are selected from the group consisting of ammonium chloride, sodium chloride, potassium chloride, calcium chloride and strontium chloride. 
     
     
         9 . A method according to  claim 4  wherein the method of at least partially removing nitric acid insoluble lead moieties further comprises at least one step selected from the group consisting of (a) providing intensive agitation or cavitating agitation to the gold-containing source material preferably ultrasonic agitation, (b) adopting a process to at least partially remove surface scale and (c) conducting the at least partial removal of nitric acid insoluble moieties at a temperature of at least 40° C. 
     
     
         10 . A method according to  claim 9  wherein the method of at least partially removing nitric acid insoluble lead moieties further comprises ultrasonic agitation. 
     
     
         11 . A method of recovering refractory gold from a material suspected of containing refractory gold comprising separating a sample from the material; subjecting the sample to diagnostic leaching; determining the lead content of the filtrate from the last 2 nitric acid leaches in preparation of the ultimate leach residue and ensuring that in both cases the lead content is less than 5 ppm;
 subjecting the ultimate leach residue to a treatment adapted to solubilise nitric acid insoluble lead moieties; analysing the filtrate from the treated ultimate leach residue for lead; wherein lead in the filtrate of the treated ultimate residue exceeds 1.5 ppm and the method further comprises treating the material with the method adapted to solubilise nitric acid insoluble lead moieties to produce a residue depleted in nitric acid insoluble lead moieties and recovering gold from the residue depleted in nitric acid insoluble lead moieties.   
     
     
         12 . A method according to  claim 11  wherein the method of at least partially removing nitric acid insoluble lead is a hydrometallurgical treatment which when applied to the ultimate residue produces a lead in filtrate which exceeds 1.5 ppm. 
     
     
         13 . A method according to  claim 1  wherein at least partially removing nitric acid insoluble provides gold recovery higher than indicated by fire assay of the material. 
     
     
         14 . A method according to  claim 11  wherein the material comprises a non-silica interferent which remains in the ultimate residue and comprises the nitric acid insoluble lead moieties. 
     
     
         15 . A method according to  claim 11  wherein the nitric acid insoluble lead moieties, when transformed and solubilised in a leach liquor are present at less than 10% of the cumulative amount of nitric acid soluble lead moieties that can be recovered in successive nitric acid leaching of the material. 
     
     
         16 . A method according to  claim 1  wherein the nitric acid insoluble lead moieties comprise sulfur-deficient lead sulfate moieties. 
     
     
         17 . A method according to  claim 1  wherein material is selected from the group consisting of playa material and copper ores. 
     
     
         18 - 21 . (canceled) 
     
     
         22 . A method according to  claim 1 , wherein the material is leached with an aqueous liquor comprising a reducing agent whereby the aqueous liquor has a negative oxidation potential. 
     
     
         23 . A method according to  claim 22  wherein the liquor has an acid pH. 
     
     
         24 . A method according to  claim 23  wherein the liquor has a pH less than 1.